AN ABSTRACT OF THE THESIS OF
Mansour Zahedi
Chemistry
for the degree of
presented on
Doctor of Philosophy
in
August 30, 1993
Title: Coherent Anti-Stokes Raman Spectroscopy (CARS) of Transient Species
Abstract approved:
Redacted for Privacy
The O.S.U. high resolution CARS facility was employed to study the CH3
methyl radical produced by the 266 nm photodissociation of methyl iodide CH3I
cooled in a free jet expansion. Rich rotationally-resolved spectra in the CH3 v1
symmetric stretching region were obtained. In the first phase of this research, the
spectroscopic properties of CH3 were the objective and many observed N,K
rotational Q-branch transitions of the u1 vibration were measured and assigned.
Because of the high translational velocity of the dissociated radicals, the lines showed
appreciable Doppler broadening and simulation of the fundamental spectrum was
necessary to extract accurate frequencies and intensities. Vibrational-rotational
molecular parameters as well as the band origin for the u1 transition and the CH
bond length were determined. This work has been reported in Journal of Chemical
Physics, vol. 96(3), 1822 (1992).
During the course of this work, a new long pulse injection-seeded Nd:YAG
laser (custom made by Continuum) was incorporated into the CARS setup. Part of
this thesis effort was devoted to the characterization and optimization of this new
laser. Because of the temperature instabilities of the seed laser, frequency locking
of the laser proved necessary. A procedure was developed in which the seed laser
frequency was stabilized to ± 8 MHz by locking the second harmonic output to the
side of a Doppler-broadened absorption line of iodine. A Doppler-free experiment
was also done which showed the laser line width to be in good agreement with the
Fourier pulse-transform limit of 10 MHz. This shows the laser to have a factor of 5-
10 higher resolution than most commercial systems. This work has been published
in Optics Letters, 18(2), 149 (1993).
The second phase of our study of CH3 radicals took advantage of the
improved resolution and shot-to-shot reproducibility of this new system. Improved
spectra were obtained of the u 1 fundamental transition 1000,-0000 (v2 = 0) as well
as of the 1100_0100 hot band transition (v2 = 1) of CH3. The frequency analysis was
extended to deduce vibrational-rotational parameters for both v2 = 0 and 1
transitions, yielding band origins of 3004.426(11) and 2996.21(4) cm-1 respectively.
From simulations of the spectra, rotational and vibrational populations were extracted
for the near-nascent distributions obtained under low density jet conditions. The
effect of collisional partners in the initial collisional heating and the subsequent
cooling of the hot CH3 radical were also examined.
COHERENT ANTI-STOKES RAMAN SPECTROSCOPY (CARS) OF
TRANSIENT SPECIES.
by
Mansour Zahedi
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
Completed August 30, 1993
Commencement June 1994
APPROVED:
Redacted for Privacy
Profess° of Chemistry in charge of major
Redacted for Privacy
Head of Department of Chemistry
Redacted for Privacy
Dean of Graduate Sc
Date thesis is presented
Typed by researcher for
August 30, 1993
Mansour Zahedi
To my wife
ACKNOWLEDGMENTS
This thesis is dedicated to my wife Ezzat, for her patience, enthusiasm, love
and constant support during my graduate study. Her understanding throughout our
many years of graduate student life is beyond explanation. I also appreciate her
loving care as a wonderful mother in raising our two sons, Amin and Ali, who have
filled our life with lots of joy.
I would also like to thank my father, who as a chemist and my high school
chemistry teacher, nurtured my interest in science. It is an honor for me to attempt
to follow in his foot steps.
I will be in debt for the rest of my life to my advisor and friend, Professor
Joseph W. Nib ler. I feel quite unable to express all the reasons for this in english.
Suffice it to say that I think the best decision I ever made was to come to O.S.U. and
work under his guidance; I would certainly do it again, and hope that many others
may be fortunate enough to do likewise.
I also wish to thank the many people in the research group who have
contributed to the success of this research. First thanks go to Dr. Kyung Hee Lee
and Dr. Kirk Brown, who introduced me to the lab. I am especially grateful to Dr.
James A. Harrison for his friendship and close assistance, and for showing me how
much fun something like data collection can be, during the last one and a half years
of my research at O.S.U. Finally, I appreciate the ongoing help of all members of
the Nib ler group, who, in the spirit of their leader, have provided a uniquely warm
and supportive research atmosphere.
TABLE OF CONTENTS
CHAPTER I
OVERVIEW
1
CHAPTER II
THEORETICAL BACKGROUND
Nonlinear Raman Spectroscopy
Description
4
4
4
7
7
8
11
12
CARS Signal
Intensity
Phase Matching Condition
Polarization Combinations for Low Frequency CARS
Resonances and Interference Effects
CHAPTER III
CHARACTERIZATION AND FREQUENCY
STABILIZATION OF A LONG-PULSE
INJECTION-SEEDED Nd:YAG LASER FOR
HIGH RESOLUTION CARS SPECTROSCOPY
. . .
Preface
Advantages of Seeded Long-pulse Lasers
Seeder Laser Crystal Temperature Tuning
Seeder Laser Frequency Stabilization
Laser Line Width Determination Using Doppler Free Experiments
Application for High Resolution Spectroscopy
Summary
CHAPTER IV
HIGH RESOLUTION STUDY OF THE u1
VIBRATION OF CH3 BY CARS
PHOTOFRAGMENT SPECTROSCOPY
Preface
Introduction
Experimental
Results
Analysis and Discussion
Assignments
Spectral Simulations
Rotational Population Distribution
Interference Effects on Frequencies
Molecular Parameters
Summary
CHAPTER V
266 nm CH3I PHOTODISSOCIATION: CH3
SPECTRA AND POPULATION DISTRIBUTION
BY COHERENT RAMAN SPECTROSCOPY
18
18
18
20
.
21
23
25
27
43
43
43
47
49
52
52
53
58
59
60
64
79
TABLE OF CONTENTS (cont.)
Introduction
Experimental
Results
Analysis and Discussion
Spectral Analysis
Collision Numbers
Vibrational Population Distribution
Spectra Simulations
Rotational Temperatures
v2 = 0 Rotational Distribution
K Conservation
v2 = 1 Rotational Distribution
Conclusions
79
83
86
89
89
92
94
96
97
98
100
102
104
REFERENCES
125
APPENDICES
133
LIST OF FIGURES
Figure
Page
2-1
Four wave mixing arrangements, (a) Collinear wave vector addition,
(b) BOXCARS wave vector addition, (c) CARS energy levels diagram 14
2-2
BOXCARS phase matching geometry with perpendicular
polarizations indicated for rotational measurements
15
2-3
Four wave mixing energy level diagrams
16
2-4
(a) Real x and imaginary x" parts of two adjacent Lorentzian,
(b) Each part is separately summed, the imaginary sum is the
Raman profile, (d) real and imaginary sum squared, (d) Final
CARS profile
17
3-1
70 ns TEM00 oscillator long pulse custom made (Continuum) Nd:YAG
laser optical layout
29
3-2
Time profile of the doubled output Nd:YAG laser pulse at 532 n m
3-3
Scan of an iodine cell using the 532 nm output of the long-pulse
seeded Nd:YAG, obtained by varying the seeder laser
crystal temperature
31
Seeder laser temperature stability scans of CO2 u1 Fermi diad at
different case temperatures
32
3-4
. .
30
3-5
Results of the seeder temperature stability scans (Figure 3-4) showing
the frequency drift of the seed laser as function of case temperature . 33
3-6
High resolution scan of the seed laser near the YAG gian maximum
over two 12 lines number 1110 and 1111
34
3-7
Seed laser stability experiment using Doppler broadened iodine line
1111
35
3-8
Doppler free experimental setup
36
3-9
Doppler free polarization spectrum of iodine line 1107 showing a
16±2 MHz effective resolution
37
3-10
Doppler free spectrum obtained for 12 line number 1108
38
3-11
Doppler free spectrum obtained for 12 line number 1110
39
3-12
CARS spectrum of the Q-branch of the 2v2 transition of CO2 taken
LIST OF FIGURES (cont.)
Figure
Page
at 2 Torr and at 298 K
40
CARS spectrum of the Q-branch of the 2v2 transition of CO2 taken
in the jet
41
Spectrum of the Q-branch of the u1 Fermi diad transition of CO2
in the jet
42
4-1
O.S.U. high resolution experimental setup
69
4-2
CARS spectra of CH3I (bottom trace, uv off) and CH3 produced by
266 nm photolysis
70
CARS spectra of CH3 produced by photolysis of CH3I at
various pressures
71
3-13
3-14
4-3
4-4
CARS spectra of CH3 produced by photolysis of 10% CH3I in He
4-5
High resolution spectrum of CH3 produced by 266 nm photolysis at
CH3I at X/D = 1 in a jet expansion of neat CH3I at 0.5 atm
73
High resolution CARS spectra of CH3, top trace is the first portion
of the spectrum shown in Fig. 4-5, middle trace is a simulated
spectrum and the bottom trace is a calculated spectrum with an
asuumed T = 540 K
74
4-6
.
72
4-7
Boltzmann fit of CH3 CARS spectrum of Fig. 4-6. The N
quantum numbers are shown, with implied K values decreasing from
left to right
75
4-8
Line shifts of calculated transitions (stick spectrum) produced by
linewidth convolutions
76
4-9
Comparison of Raman and CARS line shifts (in units of F) produced
by two adjacent Lorentzian lines of equal intensity
77
4-10
Potentail energy diagrams for CH3I (bottom) and
photodissocaition pathways for CH3I photolysis at 266 nm (top)
5-1
5-2
.
High resolution CARS spectra of CH3 produced by 266 nm
photolysis at X/D=1 in a jet expansion of 23% CH3I in argon at 2
atm. See text for discussion of assignments
CH3 CARS spectra produced by photolysis of 0.46 atm CH3I in a
78
116
LIST OF FIGURES (cont.)
Figure
5-3
Page
He jet at various driving pressures. For experimental conditions of
each spectrum see Table 5
117
High resolution CARS spectra of CH3 obtained under
near-nascent condition. The simulated spectra are also shown for
each spectrum
118
5-4
Boltzmann fit of CH3 CARS spectrum of Figure 5-3 (top spectrum).
The NK quantum numbers are shown to the right of each data point 119
5-5
CH3 rotational temperatures (assuming Boltzmann distribution)
as a function of log of total number of collisions for several carrier
gases. See Table 5 for experimental conditions
120
5-6
Relative CH3 rotational populations for individual NK states
in the fundamental region (v2 = 0) for the two near nascent spectra
shown in Figure 5-3. NK values are shown below for different K
groups. Contributions from overlapping transitions are included and
are labelled above
121
5-7
ConTarison between the CH3 NK nascent distributions of Chandler
et al. /2 and the near-nascent distributions for the two cases shown
in Figure 5-3. Only non-overlapping transitions are included
122
5-8
High resolution CARS Q-branch jet spectrum of CH3I in the u1
C-H symmetric stretching region. a) Obs. spectrum at X/D=8.
b) Calculated spectrum assuming Boltzmann distribution at 35 K.
c) Obs. spectrum at X/D=5. d) Calculated spectrum assuming
Boltzmann distribution at 50 K. e) Stick spectrum for 50 K
distribution
123
Relative CH3 rotational populations for individual K states in
the fundamental region (v2 = 0) for the two near nascent spectra
shown in Figure 5-3
124
C-1
O.S.0 new high resolutin pure rotational experimental setup
181
C-2
Q-branch CARS spectrum of u1 C-I symmetric stretch of neat CH3I
in a free jet expansion at X/D = 1
182
C-3
Pure rotational scan of air (1 Atm.). Dye laser resolution was
625 MHz and 2 laser shots were averaged
5-9
C-4
CH3I pure rotational jet spectrum. Neat sample of 400 Torr
183
LIST OF FIGURES (cont.)
Figure
Page
pressure and at X/D = 0.5
184
Simulation of CH3 pure rotational spectrum, transitions due to the
v2 hot band are also included in the calculation
185
Pure rotational jet spectrum of line S7 of N2 used as a driving
gas for CH3I
186
C-7
Pure rotational jet spectrum of line S8 of N2 in jet
187
C-8
Pure rotational jet spectrum of line S12 of N2
188
C-5
C-6
LIST OF TABLES
Table
Page
3-1
Hyperfine components of several 12 lines
28
4-1
u1 Q-branch transition frequencies for CH3 (cm-1)
66
4-2
Vibrational-rotational parameters for CH3 (cm-1)
67
4-3
Molecular parameter for CH3 and related molecule
68
5-1
Relative vibrational populations and rotational temperatures for
nascent CH3
106
5-2
vi Q-branch transition frequencies for v2=0, 1 states of CH3 (cm-1) 107
5-3
Unassigned transition frequencies and their relative CARS intensities
in the overlap region with the hot bands
111
5-4
Vibrational-rotational parameters for CH3 (cm-1)
113
5-5
Calculated rotational temperatures (Boltzmann dist.) and number
of collisions for CH3 in the jet. Experimental conditions as well
as collision diameters used in calculations are also given
114
Rotational population distribution for CH3 with calculated
Boltzmann intensities
115
5-6
LIST OF APPENDICES
Appendix
A
Quick Basic 4.5 source codes written for Tektronix digital
oscilloscope model 2440
B
C
Page
133
Quick Basic 4.5 source codes written for Stanford Research
programmable module SR245
158
CARS studies in the low frequency rotational region
178
COHERENT ANTI-STOKES RAMAN SPECTROSCOPY (CARS) OF
TRANSIENT SPECIES
CHAPTER I
OVERVIEW
Transient and short-lived reactive species have long been of interest to
chemists. A century ago, traditional studies of reaction mechanisms involved the
mixing of reactants and, after completion of the reaction, identification and
measurement of products.
This information was then used to postulate
intermediate steps and to propose the existence of transient intermediates. It was
only about the early 1920's when transient species were first directly detected in
reactive mixtures, flames, and electrical discharges by the use of optical methods.
Flash photolysis techniques developed by Herzberg and others in the 1930's were
then extensively used to generate and study the electronic emission and absorption
spectra of transient species in the gas phase. This remained the principal probe
of radical properties until, during world war II, the development of radar provided
the low frequency tuning capability needed for microwave EPR study of free
radicals stabilized by isolation in cold inert gas solids. Although no rotational
structure exists in such solid matrices, and therefore no bond lengths could be
deduced, EPR nonetheless established the existence and symmetry of many
radicals and, eventually, EPR studies of these in the gas phase became feasible.
2
It was not until the 1950's that detection of vibrational-rotational spectra of
transients was achieved in the pioneering development of rapid scan IR
spectroscopy by Pimentel and co-workers.
The other probe of vibrational-
rotational transitions, Raman spectroscopy, played no role in these early studies
of transient species because of the weak nature of the effect and the obvious low
number densities of the free radicals to be studied.
The invention of the laser in 1960 greatly improved all optical measurement
capabilities by giving an exceptionally intense light source to spectroscopists. This
has enabled rapid progress in the study of transient species by enhancing their
production, identification, and characterization by visible-uv absorption and
emission methods and by infrared techniques. In the 1970's tunable, pulsed laser
technology evolved to a state such that the nonlinear coherent Raman
measurements became possible, thus overcoming
the low sensitivity of
conventional Raman spectroscopy. In the 1980's, access to Raman transitions of
transient species finally was achieved. The high resolution of Coherent AntiStokes Raman spectroscopy (CARS) technique has made it an especially useful
tool in distinguishing rotational structure of small radicals.
In this thesis CARS has been used to study one of the most important
transient species, the CH3 radical. Species such as CH3 are of considerable
interest because they play important roles as intermediates in reactions in areas
such as combustion, atmospheric chemistry, interstellar media and plasma
diagnostics. As one of the simplest hydrocarbon free radicals, the structure and
3
properties of the planar CH3 species have long intrigued both experimental and
theoretical chemists.
The outline of this thesis is as follows. In chapter II a brief discussion of
the theory and practical applications of CARS is presented, with points relevant
to the subsequent work stressed. In chapter III the modification of our CARS
setup by incorporation of a new Nd:YAG laser is discussed and the efforts to
characterize and frequency stabilize this system are described. In chapter IV the
first phase of the research on the high resolution CARS spectroscopic studies of
CH3 is reported.
This work focusses on the spectroscopy and molecular
parameters obtained for the u1 symmetric stretching mode of the CH3 radical.
Chapter V extends the spectroscopic studies of chapter IV and covers the study
of v2 = 1 hot band as well. In addition the vibrational-rotational population
distributions of near nascent CH3 radicals are determined and the effect of
subsequent collisions by various gases is examined.
4
CHAPTER II
THEORETICAL BACKGROUND
Nonlinear Raman Spectroscopy
Description
The first observation of a coherent anti-Stokes Raman (CARS) signal was
made by Maker and Terhune in 1965.2 Along with subsequent improvements in
experimental methods, the theory of various coherent Raman processes has
developed to a remarkable level in the past couple of decades. This chapter
provides a brief sketch of some of the relevant aspects of this theory, as applied
to the research discussed in the following chapters. For more details on the
theory, the reader is referred to the references at the end of the chapter.1-25
In a classical view of the interaction of matter with an electric field, the
polarization (dipole moment per volume) induced in a medium is written as a
power series in the electric field E5
P = X(1) -E X (2) EE + x(3) :EEE
2-1
Here, x(n) is the susceptibility of order n and the term x(3) is the third order
5
susceptibility, which is responsible for all coherent Raman phenomena such as
CARS, CSRS (coherent Stokes Raman scattering), SRG (stimulated Raman gain),
SRL (stimulated Raman loss) and PARS (photoacoustic Raman scattering).
The third term of Equation 2-1 corresponds to a four wave mixing process
since it can involve three input beams at frequencies 6)0, 6)2, and co 1 which couple
in the medium through its susceptibility to yield a fourth wave which emerges from
the sample at one of the frequency combinations
6)3 =
± (A)1± (I) 2
In the case of CARS, the induced oscillating polarization oscillates at ca3 =
Wl
2-2
+
6)2 and is written as
P((3)
)3)
x(3) [4)3,4)0,4)1,(021:E0. E 1.E;
2-3
For experimental simplicity a three-wave variant is often used for CARS in which
4)0 is chosen to be equal to (01, termed the pump beam, while 4)2 is called the
Stokes beam. The signal, called the anti-Stokes beam, is at 4)3 = 24)1 - 4)2 = 4)1
+ A wvib for vibrational CARS studies where the resonance condition is A wvib =
- 4)2 Since 6)3 is higher in frequency than 6)1 by A covib, spectral filters can be
used to eliminate the unwanted 4)1 and 4)2 scattered photons and one has the
advantage that the signal occurs in a spectral region where fluorescence of the
medium and other materials is not a problem.
6
For pure rotational CARS studies however, the pump and Stokes
frequencies are almost identical and discrimination of w3 from these is difficult.
In this case a four wave experiment is favored in which one chooses coo (pump)
and w2 (Stokes) both in the yellow (or red) region of the spectrum. These beams
act to drive the Raman resonance. The induced polarization is then probed by an
w 1 beam in the green region so that it is possible to eliminate the pump and the
Stokes scattered photons easily by the use of filters and a monochromator.
Discrimination of w3 = wi + (00 - w2) = w 1 + A wrot from the scattered w 1 (green)
photons can be achieved with a polarizer since the signal beam and the green
beam will have orthogonal polarizations if those of wo and w2 are orthogonal.
Equivalent discrimination can be obtained by using an iodine vapor cell as a sharp
filter; more details about this latter method are given in chapter III.
The fact that the signal at (A)3 is coherent and has all properties of a laser
originates from the fact that the induced polarization (Equation 2-3) is coherently
generated in the medium (i.e. many molecules are caused to vibrate in phase at
wo - w2) Contrary to conventional incoherent spontaneous Raman spectroscopy
where the scattered photons have random phases, in CARS the stimulated
emission is coherent. The resultant in-phase addition of anti-Stokes amplitudes
produces large signal gains (-106) over conventional Raman scattering and it
greatly increases the collection efficiency since the signal is both unidirectional and
single frequency.
7
CARS Signal
Intensity
The time averaged intensity of the anti-Stokes signal is given by the
relation84
13 = 256 7r4 (41(nonin2 n3 C4 ) I XTARS 12 /0 /1 /2 /2 [sin(Ak//2)/(6, k//2)]2
2-4
where 1i and ni are the intensity and index of refraction, respectively, of the ith
laser beam, x(3) is the third order susceptibility, E. is the interaction length, and Ak
= ko + ki - k2 - k3 is the phase mismatch. Since 13 0= 10 II
12 ,
the use of
focussed lasers with high peak intensity is greatly favored. The x(3) term in
Equation 2-4 contains all of the spectroscopic information of interest and is given
by10
(3)
XCARS=XNR± E C4/(4t16342) X (Ni-Nf)/(6)fi-630+632-irfi) X (a Gfi
No)
2-5
v'
where xNR is the nonresonant susceptibility. From Equation 2-5, the resonance
condition is seen to occur when Wri = Wo - W2 . The term (do-Mi) is the
spontaneous Raman cross section and Ff., is the natural Raman linewidth of the
transition which is identified as the halfwidth at half maximum (HWHM).
As Equations 2-4 and 2-5 indicate, the CARS signal intensity is directly
proportional to the square of the population difference (Ni Nf) of the initial and
8
the final states involved in the resonance process. In the vibrational region, most
of the population is in the ground vibrational state and the Nf term does not
contribute much. In the pure rotational region however, CARS signals are in
general weaker due to the fact that the population difference tends to become
smaller as the two resonance states become closer and therefore there is a higher
chance for the population to be distributed over many closely spaced levels. In
this case a significant enhancement of the CARS signal can be achieved by cooling
the gas samples in a free jet expansions so as to concentrate the population within
fewer states.
Phase Matching Condition
In Equation 2-4 the last term [sin(Akt/2)/(Ake/2)] 2 will be a maximum
(equal to one) when Ak = 0, i.e. the exact phase matching condition is satisfied.
This corresponds to the wave vector addition
A k = k3- /co
ki +1c1= 0
2-6
where I ki I = niwi/c with ni being the refractive index at wi. Shown in Figure 2-1
(a) is a vector diagram for the common collinear phase matching arrangement.
For such collinear beams focussed by a lens of focal length f, -75% of the CARS
signal is generated within a length of 6b (where b is the confocal parameter b =
irw02/2),. and w0 is the focal waist diameter NI = 41f/irw for a Gaussian beam of
diameter w).84
A wave vector diagram for an alternative, folded-BOXCARS86 phase
9
matching scheme (trace b) as well as a CARS energy level diagram (trace c) is
also shown in Figure 2-1. Here the signal level is generally lower (- a factor of
10) due to the decreased interaction length of the crossed beams. However, this
geometry is advantageous in that the signal generated is spatially separated from
the unwanted Stokes and pump beams so that, with a simple aperture, one can
discriminate against them. Another big advantage of this geometry is the tightness
of the size of the beams at the probe volume due to the crossing angle. This
feature becomes important when one needs spatial resolution to probe molecular
beams along the jet axis in expansion experiments. A third advantage of the
BOXCARS geometry is that the contribution of the nonresonant third order
susceptibility from the optics and the background gas is greatly reduced because
the beams only overlap at the focus. This is particularly significant when one
works in the pure rotational region where the resonance signals are inherently
weaker for the reasons discussed earlier.
In order to derive an expression which relates the physical spacing
of the
four BOXCARS beams on the focusing lens to the wavelengths of the four waves,
one can write the three components of the wave vectors along the three Cartesian
coordinates shown in Figure 2-1 (b) as:
A k=k3-ko-k+k2=0
2-7
10
Akz = 1k3 Icos03
lko Icos00 -Iki Icosei + 1k2 Icos02 = 0
2-8
1k1 'sine = 0
2-9
A ki=1k0 I sin00
A ky=1k3Isin03- Ik2Isin02=0
2-10
As shown in Figure 2-2, for input and output lenses of common focal length f, the
distance Pi from the lens center to each of the beam spots on the lens is
ki = f tan 0i
2-11
Combining this relation with the Equations 2-8 to 2-10 and knowing that I ki I =
nioi/c one can solve for all four values of 0i, and hence Pi, once one of these is
chosen. For gases ni is essentially unity, for small 0i, it can be seen that Pi is
essentially proportional to li so that, for the beam with the shortest wavelength,
the distance from the lens center is shortest. This point is pictorially illustrated in
the view of the output lens from the focus for the BOXCARS geometry in Figure
2-2. Proper spacing of these beams would be especially critical when there are
large wavelength differences in the mixing process.
11
Polarization combinations for low frequency CARS
The polarization directions of the laser beams are also important in four
wave mixing experiments.
For vibrational CARS the greatest intensities are
obtained via the third order non-linear susceptibility term 6x
(3) where the x's
refer to the electric field Ei polarization directions of the CARS beams with the
order i = 3, 0, 1, 2 from left to right respectively. Here all four waves are
vertically polarized and the effective polarizability tensor element sampled is x
- a230 = a2 = a2zr 6 For a crossed polarization experiment, one measures x
YY
-
a2
xY
which is much smaller for strongly polarized vibrational transitions. For
rotational CARS measurements however, the transition is depolarized and one can
take advantage of an orthogonal polarization arrangement such that the resulting
CARS signal at 633 emerges from the sample with a polarization orthogonal to that
of the co 1. In this way discrimination against the green scattered photons at w I
becomes possible by the use of a polarizer. The effective third order susceptibility
in this case has the form 6xxyxy and the polarizability element sampled is axy2 =
3/4 a ,a2.6 The polarization arrangement corresponding to the resonance condition
of Figure 2-1 (c) is illustrated in Figure 2-2 in the view of the output lens from the
focus for the BOXCARS phase matching geometry. An equivalent signal would
be obtained if all polarizations are rotated 90°. It may be noted that the best
signal condition is for the 647 Kr+ line to be ca2 and the tunable dye wo to be
scanned to higher energy.
12
Resonances and Interference Effects
Schematic diagrams of the spontaneous Raman (a) and the three types of
processes that contribute to the CARS signal are illustrated in Figure 2-3. The
two processes c and d contribute to the xNR term and represent all of the off-
resonant vibrational and electronic contributions as well as the two photon
electronic transitions such as cafi - 26)2 which add to the x(3) signal produced by the
process of interest b. For pure compounds at resonance (co fi = (o2 -
6.) 1), the
nonresonant term xNR is small in comparison with xR but for dilute mixtures, xNR
can be comparable to xR since it comes from all species in the medium. The total
CARS signal intensity is proportional tol°
I X CARS
12 =E Ixii-xNR12+ 1 x112
2-12
where xi, is the real part of the susceptibility term i and xi" is the imaginary part
(Note that xNR is purely real, in the absence of absorption). In the spontaneous
Raman process the only contributing term
is
the imaginary part of the
susceptibility, xi". For CARS however, one can have interferences between the
various contributing terms in the Equation 2-12.
In the CARS case, due to the dispersive shape of the real part of the
susceptibility xi ' , the I xi ' 12 term tends to build up intensity out in the wings of
two adjacent peaks while it has the effect of canceling out some of the intensity
in the region between the peaks. The net effect of this interaction of the two
13
parts of the susceptibility on the two closely spaced CARS peaks is to cause a
small outward shift from the central positions. Thus, for accurate measurement
of transition frequencies and in deducing spectroscopic constants in a high
resolution study one must take proper account of these shifts due to interference
effects.5 Another effect of the summation of real and nonresonant susceptibility
terms in Equation 2-12 is to cause the CARS lines to have a nonsymmetric shape,
in contrast to that of the spontaneous Raman. Figure 2-4 illustrates these
interferences for two closely spaced Lorentzian profiles. Trace (a) shows real and
imaginary parts while trace (b) is the separate sum of them. The spontaneous
Raman profile is thus shown as sum(x"). Trace (d) shows the CARS line shape
obtained by summing the separately squared parts of the susceptibility trace (c).
Trace (d) also suggests the slight shift in the peaks position due to the interference
effect. More details about these effects are given in chapter IV.
Despite some of these lineshape complications of CARS, work in our
laboratory has shown it to be a valuable technique in studying molecules in the gas
phase and in probing molecular clusters found in free jet expansions. In this
thesis, CARS is applied to yet another challenging problem, the spectroscopic
study of transient species. The result of such studies on methyl radical are
presented in chapters IV and V.
14
I;
>
k0
It >.
il
(a)
1k31>lk11>lk01>lk2 I
wi
w
Z
(b)
Y
A
6)3
2
(c)
Figure 2-1. Four wave mixing arrangements, (a) Collinear wave vector
addition, (b) BOXCARS wave vector addition (c) CARS energy levels
diagram.
15
co 3 signal
x
View of output lens from focus
Figure 2-2. BOXCARS phase matching geometry with perpendicular polarizations
indicated for rotational measurements.
For vibrational measurements, all
polarizations are vertical (X). The distances E. are exaggerated.
16
W3
CO2
6)()
(a) Spontaneous Raman
W1
(b) CARS
631
6)2
6)
o
(02
()3
6)1
6.)3
W1
(d)
(c)
Nonresonant Processes
Figure 2-3. Four wave mixing energy level diagrams.
17
(b)
Sum
Sum x'
x'
-20
-10
10
20
-20
(c)
-10
10
20
(d)
(
CARS 1 x 12
II
(x')2
-20
-10
J
_
0
10
20
-20
-10
10
20
Figure 2-4. (a) Real x ' and imaginary x" parts of two adjacent Lorentzian, (b)
Each part is separately summed, the imaginary sum is the Raman profile, (d) real
and imaginary sum squared, (d) Final CARS profile
18
Chapter III
CHARACTERIZATION AND FREQUENCY
STABILIZATION OF A LONG-PULSE INJECTION-SEEDED Nd:YAG
LASER FOR HIGH RESOLUTION CARS SPECTROSCOPY
Preface
During the course of this research, a new Nd:YAG laser was incorporated
into the high resolution CARS system at O.S.U. This chapter describes our efforts
to characterize the frequency resolution and to lock the frequency. This work has
been published in Optics Letters, 18(2), 149 (1993), and this paper is reproduced
below, along with a few expansions of the discussion.
Advantages of Seeded Long-pulse Lasers
Injection-seeded
Nd:YAG
lasers26
offer
several
advantages
to
spectroscopists. As an example of a high resolution application, Esherick and
Owyoung obtained sub-Doppler polarization spectra of gas phase iodine by
scanning an injection-seeded Nd:YAG system with near Fourier transform-limited
bandwidth (s40 MHz) at 532 nm.27 The reproducible single mode operation of
seeded lasers is also important in that it gives rise to smaller shot-to-shot intensity
19
fluctuations,28 an especially useful feature in coherent Raman spectroscopies.
Additional benefits have been realized in coherent anti-Stokes Raman
spectroscopy (CARS) when the temperature, and hence frequency, of the seed
laser is carefully controlled. Tuning the doubled-frequency of the seeded laser to
the peak of an iodine vapor absorption allows the occasional unneeded shots to be
sensed, and rejected, by monitoring the transmission through an 12 cell.
Furthermore, another 12 cell can then be used as an exceedingly sharp spike filter
to eliminate 532 nm background light from the frequency-shifted CARS signal.29
Some of the characteristics of a novel injection seeded Nd:YAG system
which is recently being utilized for high resolution coherent Raman spectroscopy
at O.S.U. are described here. An optical layout of this laser is given in Figure 3-1.
The key elements are a diode pumped, monolithic" Nd:YAG seed laser
(Lightwave Electronics Model 122-1064-50F) which drives a custom high power
pulsed laser built by Continuum. The latter consists of a 6 mm diameter oscillator
rod in a 2 m TEM00 stable resonator configuration which is operated near
threshold and Q-switched to give -7 mJ 1064 nm pulses at 20 Hz and with a
FWHM of -55 ns. These are then sent sequentially through a Faraday isolator,
7 and 9 mm amplifier rods, telescopes, and a 50 mm type II KDP* doubling
crystal, yielding 150-200 mJ 532 nm pulses of 35-45 ns widths. Seeding is achieved
by injection of -9 mW cw 1064 nm light into the oscillator via a polarizing
element. The cavity length is stabilized with a piezoelectric end mirror using a
commercial Faraday isolator and mirror control system (Lightwave Electronics
20
Model S100, sans seed laser).
This laser is unusual in that its long pulse duration (-45 ns at 532 nm) gives
5-10 times greater resolution than conventional systems. A temporal profile of the
frequency doubled output of the laser at 532 nm is illustrated in Figure 3-2. This
trace was obtained by interfacing a Tektronix digital oscilloscope (Model 2440
programmable oscilloscope) with a personal computer. Since this is the first such
application of the 2440 scope, copy of the computer codes is provided in appendix
A.
Seeder Laser Crystal Temperature Tuning
The seed laser temperature control electronics provide for convenient
frequency scanning of the laser over a range of -2 cm-1 (Figure 3-3). For this
trace, <1 mJ of 532 nm light was sent through a 174 mm glass cell containing 12
vapor at room temperature (ca. 300 mTorr31). The light was attenuated to ensure
that saturation did not occur and was spatially integrated with opal glass placed
several cm in front of a photodiode detector. A similar setup without a cell was
used to provide a normalizing reference and both signals were sent to a pulse
integrator (Stanford Research Systems Model SR250), digitized using a
programmable computer interface module (Stanford Research Systems Model
SR245)
,
and stored in a microcomputer. For scanning, the above module was
interfaced with a computer to generate an analog voltage which was stepped (10
mV/step) and sent to an external temperature control input on the seed laser
21
electronics. A list of this computer code is included in appendix B. At modest
scan rates of 20 MHz/s, the oscillator piezo servo system was easily able to
maintain single mode operation, interrupted only by periodic resets of the piezo
mirror. These resets were sensed by the computer and the corresponding data
points collected during the reset duration were rejected.
This scan of Figure 3-3 encompasses iodine atlas32 lines 1106 to 1113 for
our seeder temperature variation from 50 to 20 °C but extensions to lines 1104
and 1116 can be achieved by operating the pulsed laser oscillator crystal at higher
or lower temperatures.27'33 Also shown in the figure are assignments and absolute
frequencies, corrected from the iodine atlas values by subtraction of 0.0056 cm-1.34
In scanning, the seed laser was observed to change mode periodically, jumping
back 20 GHz about every 32 GHz scanned. In each mode range, a somewhat
nonlinear scan was observed, with a scanning coefficient determined to be:
avlat(MHz1°C)= -5768 +66 xt+ 1.5 xt2.
3-1
Seeder Laser Frequency Stabilization
A smaller but significant frequency variation was noticed when the seed
laser crystal temperature is fixed but the overall seed laser case temperature
increased -5 °C; the temperature coefficient in this instance was -320 MHz/°C.
This value was obtained by taking CARS spectra of the CO2 molecule in the u 1
Fermi diad region at various case temperatures (Figure 3-4) and making a least
22
squares fit of the frequency shifts against the case temperature. The result of the
fit is illustrated in Figure 3-5. The positive slope of 320 MHz/°C suggests that
the stabilizing electronics are themselves temperature sensitive, a troublesome
feature if a fixed frequency output is required. Although one could control the
case temperature, we chose to lock the output to an absolute reference such as 12,
as described below.
For locking purposes, we selected the midpoint of the steep high frequency
side of the 1111 line at 33 °C, near the gain maximum of the pulsed laser. A high
resolution scan of the 1110 and 1111 lines is illustrated in Figure 3-6. This 50%
value is calculated to be at 18788.4624(7) cm-1 from a calibration of the scale
using the fitted peak maxima. The result of the fit using a Gaussian line shape
function is also shown in the same figure. The 50% point has an absolute
uncertainty of 0.0007 cm-1 but it can clearly be set more precisely than the
relatively flat peak maximum. A variation of ±5% transmission corresponds to
holding the frequency stable to ±26 MHz. Analog circuits to hold the frequency
stable to this level are relatively simple to construct but, for demonstrating
feasibility, a computer was programmed (appendix B) to hold the 50% level
constant, yielding the results shown in Figure 3-7.
To control this midpoint, 20 normalized transmission measurements were
averaged and, after comparing the average to the initial 50% value, the seeder
control voltage was stepped up or down 0.5 mV (1 MHz) each second. As shown
by the middle trace of Figure 3-7, the slow case temperature drift, and possibly
23
other factors, caused a correction voltage to be sent to the seeder. This
correction, sampled once a minute, is displayed as the MHz shift that would have
occurred in the absence of locking of the 50% point and is calculated from a
separate determination of dv/dV by scanning over lines 1110 and 1111 (Figure 3-
6). The cell transmission, also reported once a minute, can be expressed in terms
of MHz using the measured slope at the 50% position and this is shown as the
upper trace of Figure 3-7.
The standard deviation of this trace (3.4%
transmission) implies a ±18 MHz frequency uncertainty, but this is a maximum
since a good fraction of this deviation comes from laser pulse energy fluctuations,
not frequency variations.
A better measure of the short term frequency
fluctuations can perhaps be obtained by displaying (lower trace) the minute to
minute changes (derivative) of the correction voltage. The standard deviation of
this quantity is ±8 MHz, a value which includes a measured ±3 MHz dither
broadening of the piezo servo electronics.
Laser Line Width Determination Using Doppler Free Experiments
An improved procedure might employ locking to one of the 12 hyperfine
components which can be resolved if one uses a Doppler-free method such as the
Wieman and Hansch technique.35 A second motivation for making such a
measurement is to determine the actual laser linewidth (the theoretical Fourier
limit for our 45 ±2 ns pulse is 10 ±1 MHz, Figure 3-2). Accordingly, a Doppler
free polarization experiment was performed in which a 1µJ pump pulse (45°
24
polarization) was passed through the 174 mm cell with 12 at -100 mTorr and a
vertically polarized 0.1 AJ probe beam was counter-propagated collinearly. A
schematic diagram of the Doppler free experimental set up is shown in Figure 3-8.
To carry out the experiment the probe beam was nulled off resonance by use of
a quarterwave plate followed by an analyzing polarizer and the residual light,
reduced by -104, was detected by a photomultiplier (Hamamatsu Model R955).
A signal was then produced by changes in the probe polarization when the pump
and probe frequencies were scanned into resonance with the zero velocity
subgroup of molecules. A normalizing signal, as for Figure 3-7, was also used.
Figure 3-9 shows the resultant Doppler free spectrum produced by scanning
the seed laser over line 1107, R(86) 33-0; for comparison, the normal Doppler
broadened absorption is shown at the top. Most of the predicted 15 components
of this even-J line (21 components for odd J) are resolved. The pattern can be
easily analyzed using the hyperfine splitting relation derived by Levenson and
Schawlow (equation 8 of Ref. 36) and a least squares fit yields the relevant
parameters A(eQq), the difference in the quadruple field gradients of the two
states, and A AGexp/I, the change in magnetic spin-rotation interaction. Three
even-J transitions 12 lines 1107, 1108, and 1110 (Figure 3-9 to Figure 3-11) were
examined in detail and the results are summarized in Table 3-1. It should be
noted that the values of A (eQq) are close to those given for other J > 20 states
similarly measured using a 514.5 nm argon ion laser.36
At the bottom of Figure 3-9 is a spectrum calculated using a best fit
25
Gaussian broadening of 16±2 MHz. The broadening due to the dither used in the
piezo adjustment circuit was determined to be 6±1 MHz. (This could probably
be reduced by half without loss of seeding performance.) Since the natural
linewidth and collision broadening at 100 mTorr are negligible (<1 MHz) the
residual width of 10±3 MHz reflects the laser linewidth, a value which is in good
agreement with the Fourier limit of 10±1 MHz. For the Fourier transform
calculations we have assumed Gaussian shapes for which AtAv = 21n2hr, where
At is the FWHM in time and A v is the FWHM in frequency.
The well-resolved hyperfine components indicate that their use for
frequency locking37 of this pulsed system is feasible. This is probably of marginal
gain, however, since locking to the Doppler broadened peak gives stability
comparable to the linewidth. It is useful to mention that an alternative approach
would be to lock the cw 1064 nm seed laser output directly to an absorption or
one of its Doppler free components. Cesium dimer has been suggested for such
a purpose and its Doppler free spectrum near 1064 nm has been published.38 In
addition, a table of reference frequencies for CS2 in this wavelength region has
been compiled.33'38
Application for High Resolution Spectroscopy
To demonstrate the resolution capabilities of the OSU CARS apparatus
utilizing this laser, a scan of the Q-branch structure of the 2v2 Fermi diad
spectrum of CO2 at -298 K is shown in Figure 3-12. In this experiment, the
26
Nd:YAG frequency was fixed and the output divided to serve as both a CARS
pump beam and as an amplifier for a cw single frequency dye laser (Coherent 699-
29). The three main contributions to the peakwidths are the Doppler width, the
collisional width, and the instrumental width. For the well resolved J=24-32 lines
the calculated Doppler width at 300 K and for the 0.04 radian crossing angle of
the pump and Stokes beams is 84 ±4 MHz.39 The collisional width at 2 Torr is
8.-± 1 MHz.4° A CARS simulation program using these parameters then yields a
value of 43 ±15 MHz for the instrumental resolution of our CARS spectrometer.
This value is in good accord (1.3 greater) than the best case CARS resolution of
33 MHz derived from the Fourier transform linewidth (plus dither) of the
Nd:YAG (16 ±2 MHz) and of the amplified dye (17±1 MHz from a measured
26±2 ns pulsewidth). It is good to note that, for stimulated Raman gain/loss
spectroscopy, the resolution would be even better since it is determined by the
amplified dye only (the cw probe beam resolution being <1 MHz).
As the Doppler width is by far the largest broadening contribution, ways to
decrease this are desirable. Vibrational studies of samples cooled to 10-90 K in
free jet expansions would benefit from a corresponding 2-5 fold decrease in the
Doppler width. This fact is illustrated in Figure 3-13 by scanning the same region
of spectrum of CO2 but using a 10% mixture in Helium and probing the molecule
at a X/D=12 along the jet expansion axis. The top trace is the observed spectrum
while the bottom trace is calculated using the simulation routine and the same
instrumental as well as collisional width but with a Doppler width of half the value
27
used for the spectrum in Figure 3-12. Extension of these studies to lower Raman
shift transitions in the pure rotational region41 can further reduce this width to less
than 1-2 MHz. Collisional widths are also negligible if the jet is probed beyond
a few nozzle diameters from the opening so that the high resolution of this pulsed
laser system will be especially useful in studies of molecules cooled in such
expansions.
Figure 3-14 is a demonstration of the combined advantages of
employing this high resoluton long-pulse laser in a free jet expansion experiment
to resolve one of the narrowest Q-branch structures known. This scan is taken
from the u1 Fermi diad of CO2 and it clearly reveals some of the structure under
this extremely sharp transition.
Summary
The frequency tuning and stabilization of a novel long-pulse seeded
Nd:YAG laser is described. The laser frequency was stabilized to ±8 MHz by
locking it to an iodine absorption transition near the gain maximum of the pulsed
laser. A Doppler free experiment shows the laser linewidth to be in good
agreement with the Fourier transform limit of 10 MHz. Molecular hyperfine
frequencies and parameters were determined for three 12 absorption lines. The
use of this laser as a pump and a cw probe amplifier for CARS spectroscopy is
illustrated by a scan of the Fermi diad pairs 2v2 and v1 Q-branch transitions in
CO2, and the instrumental resolution is found to be 43 ±15 MHz.
28
Table 3-1. Hyperfine components of several 12 lines
12 atlas line #
1107
1108
1110
vo lit. (cm-1 )a
18787.2800(4)
18787.3389(3)
18788.3371(6)
vo cal. (cm-1 )
18787.2806(2)b
18787.3394(2)
18788.3391(1)
A(eQq) MHz
1900(54)
1888(40)
1813(18)
LIO.LG)/I MHz
0.135(36)
0.123(22)
0.100(26)
Quantum Number
Obs.
Obs.-
Obs.
Obs.-
Obs.
Obs.-
mic
Shiftd
Cal.
Shift
Cal.
Shift
Cal.
M2
2.5
-2.5
-463
4
-459
5
-413
-4
-1.5
-2.5
-213
23
-224
16
-159
28
1.5
-2.5
-177
10
-186
3
-130
8
2.5
-1.5
-177
-7
-169
-1
-130
-1
2.5
2.5
-140
-20
-129
-12
-102
-21
-0.5
-2.5
-64
12
-75
6
-19
15
0.5
-2.5
-49
9
-58
4
-3
12
2.5
-0.5
-13
-3
-11
-2
35
12
2.5
0.5
5
-3
7
-2
35
-7
1.5
-1.5
117
6
111
4
143
1
-0.5
-1.5
233
13
222
7
267
21
0.5
-1.5
242
4
239
5
267
3
1.5
-0.5
277
7
275
9
299
4
1.5
0.5
277
-11
275
-10
299
-15
0.5
-0.5
399
0
395
2
419
2
a See Refs. 32, 34
b Values in parenthesis are standard errors from fitting procedure and do not
include the absolute uncertainty of v0 values nor contributions from any small
local nonlinearities in the temperature scanning of the hyperfine structure.
M1 and M2 are the components of the nuclear spin of iodine atom 1 or 2 on the
molecular axis. See Ref. 36.
d The uncertainty (MHz) of the observed shift frequencies is 25 + 0.12 x (Obs.
Shift).
29
20
18
11
6
16 15
17
13 12 11
1
1
/
14
21
3
lb
11
2
3
4
%4
5
3
6
3
7
% 11
T I
/
/
10
Seeder
\
I
seeder
telescope
10
10
beam
dump
la. Mirror, rear, +5 m
13. Apodizer, soft, 4 mm
lb. Mirror, rear, +2.4 m
2. Pockets cell
14. 7x115 mm rod, flashlamps
15. Div. lens, -120 mm
3. 1/4 plate
16. Con. lens, +155 mm
4. Polarizer, dielectric
5. Pinhole, 1.5 mm
6. 6x115 mm rod, flashlamps
7. Wedge
8. 1/2 plate
9. Faraday rotator
10. Mirror, turning, 45°
11. Div. lens, -104 mm
17. 9x115 mm rod, flashlamps
18. SHG, Second Harmonic Generator
19. Dichroic, 532 nm
20. THG, Third Harmonic Generator
21. Dichroics, 355 nm
22. Reflector, 20%, 45°
23. Faraday isolator
12. Con. lens, +300 mm
Figure 3-1. 70 ns TEMP oscillator long pulse custom made (Continumm)
Nd:YAG laser optical layout.
30
PREDICTED FOURIER
1
I
I
A v ..a t=21n2/7c
Av= 10 MHz
At
43.4 ns
I
-120
I
-80
I
I
-40
I
I
0
I
I
40
I
I
80
I
120
TIME (ns)
Figure 3-2. Pulse profile of the doubled output of the Nd:YAG laser at 532 nm.
31
1106 18787.1285(4)
1108 18787.3389(3) 1110 18788.3371(6) 1112 18789.0256(6)
P (119) 35-0
R (56) 32-0
R (106) 34-0
1107 18787.2800(4) 110918787.8042(6)
R (86) 33-0
1111 18788.4454(7)1113 18789.2769(4)
R (134) 36-0
P (83) 33-0
1
P (142) 37-0
P (103)34-0
P (53) 32-0
Mode Hops
R (121) 35-0
I
I
1
#*
lov
I
il
i
)
00
0
0 Il
r..1
.0
0 00
-4 0
VD
-4
14
N
0
11
I
50
I
46
I
I
42
I
1
38
I
I
34
I
I
30
1
I
26
I
I
22
SEEDER TEMPERATURE (C°)
Figure 3-3. Scan of an iodine cell using the 532 nm output of the long-pulse
seeded Nd:YAG, obtained by varying the seeder laser crystal temperature. Seeder
laser mode hops of -20 GHz are marked by arrows. The frequencies and
rotation-vibration assignments are from Refs. 32, 34.
32
1387.97
1388.01
1388.05
1388.09
1388.13
WAVENUMBERS
Figure 3-4. Seeder temperature stability scans of CO2 v1 Fermi diad at
different case temperatures.
33
CRYSTAL CASE TEMP. C°
Figure 3-5. Result of the seeder temperature stability scans (Figure 3-4)
showing the frequency drift of the seed laser as function of case temperature.
34
l'AJ1
18788.4639
50 470--
18788.4624
40
18788.4610
0%
# 1110 18788.3371(6)
18788.3
# 1111 18788.4454(7)
18788.4
18788.5
WAVENUMBERS
Figure 3-6. High resolution scan of the seed laser near the YAG gain
maximum over two 12 lines number 1110 and 1111.
35
+5
60 %
I
0
\II
I
i
40
-50
30.1 (Case Temp.)
30.2
300
29.:
250
Unlocked
29.
29.4
100
29..
29.2
Locked
50
ii,Lti Al,..1,...Likk.i..i7 ,LI. Thr,Aa ivi A,....1, gytilli.,,T 1,,Ti
0
50
I
0
I
50
I
I
I
I
100
TIME (MEN.)
yil
,
I
I
150
Figure 3-7. Seed laser stability experiment using Doppler broadened iodine line
1111. The upper trace is the variation of the 50% locking point, expressed in
MHz, and is a maximum since it includes a large contribution from shot-to-shot
intensity fluctuations. The lower trace is the minute to minute frequency
correction applied to the seeder while locking, and the middle trace is the
calculated frequency drift which would have occurred in the absence of locking.
36
PMT
Seeded Long
Pulse Nd:YAG
L
PH
V
to
electronics
OG
ND
F-1> to electronics
PD
A - variable aperture
lin - waveplate
GT - Glan-Thompson polarizer
BS - beamsplitter
ND - neutral density filter
PH - pinhole
L - lens
OG -opal glass
Figure 3-8. Doppler free experimental setup.
37
12 Line Number 1107
18787.2800(4)
CALC. 16 MHz
I'
11
I
milli
,,
-800
-400
i
1
,-___-.1 ,--
,,
0
400
800
SHIFT (MHz)
Figure 3-9. Doppler free polarization spectrum of iodine line 1107 (middle trace)
showing a 16 ±2 MHz effective resolution. The lower trace is the calculated
spectrum using the parameters in Table 3-1. The Doppler broadened absorption
is shown above.
38
12 line Number 1108
18788.3389(3)
1
-800
IIIIIIIIIIIIIII
-600
-400
-200
0
200
400
600
Shift (MHz)
Figure 3-10. Doppler free spectrum obtained for 12 line number 1108.
800
39
I2 Line Number 1110
18788.3371(6)
\
II
-800
-600
I
I
-400
I
I
-200
I
I
0
)
I
I
200
I
I
400
I
I
I
600
Shift (MHz)
Figure 3-11. Doppler free spectrum obtained for 12 line number 1110.
800
40
20
J-0
10
30
I
1285.4
I
I
1285.5
I
I
1285.6
1
1
1285.7
WAVENUMBER
Figure 3-12. CARS spectrum of the Q-branch of the 2u2 transition of CO2
taken at 2 Torr and 298 K.
41
JET, X/D=12, 10%/He
CAL., T-12 K
111-111
1285.88
1285.92
1111
1285.96
1286
WAVENUMBERS
Figure 3-13. CARS spectrum of the Q-branch of the 2u2 transition of CO2
taken in the jet. The bottom spectrum is calculated assuming Boltzmann
distribution.
42
12% IN He
x/D=5
CAL.
1
16
24
STICK SPEC.
0
40
48
1
1
1388.14
1388.16
1388.18
1
I
1388.20
1388.22
WAVENUMBERS
Figure 3-14. Spectrum of the Q-branch of the v 1 Fermi diad transition of CO2 in
the jet. The top trace is the experiment. The bottom trace is the calculated stick
spectrum with the corresponding J quantum number assignments. The middle
trace is the convoluted spectrum.
43
CHAPTER IV
HIGH RESOLUTION STUDY OF THE v1 VIBRATION OF CH3
BY CARS PHOTOFRAGMENT SPECTROSCOPY
Preface
The research described in this chapter concentrates on spectroscopic
aspects of the CH3 radical, produced by photolysis of CH3I. This work has been
published in Journal of Chemical Physics, vol. 96(3), 1822 (1992), and the following
is essentially this paper with minor additions.
Introduction
The methyl radical
is
an important reaction intermediate in many
combustion and photochemical processes, and as one of the simplest hydrocarbon
free radicals, its structural and spectroscopic parameters have been of considerable
interest for many years.42-58 The production of CH3 by UV photolysis of CH3I
has been especially studied,59-83 as this fragmentation process has long served as
a model for polyatomic photodissociation. The nature of the dissociative potential
surface is now known in considerable detail and Morokuma59 has discussed the
efforts to bring theoretical and experimental results for fragment energy
44
distributions into accord. Although the latter have been extensively studied, there
remain some uncertainties about the full rotational and vibrational state
distribution of the CH3 from the CH3I photolysis.
In this work, the value of coherent anti-Stokes Raman spectroscopy
(CARS) in the vibrational-rotational study of CH3 produced by 266 nm photolysis
of CH3I is demonstrated. It is also shown that the sensitivity of CARS is adequate
for detection of CH3 photolyzed in jet-expanded samples of CH3I so that product
distributions can be probed for rotationally-cold parent molecules. The high
resolution of the technique permits observation of individual N, K Q-branch
transitions of the symmetric stretch and thus allows a direct determination of
relative vibrational-rotational populations. In this chapter the focus is on the
spectroscopic analysis of the main band transitions (1000)(0000) of the methyl
radical spectrum, while in the next chapter more attention is paid to the frequency
analysis of the hot band spectrum (1100)+40100) as well as a more detailed
population analysis.
The molecular parameters of the methyl radical have been sought for many
years but have been difficult to obtain because of its short lifetime and the absence
of electronic transitions in the visible and near-UV. The first spectroscopic
observation was by Herzberg and Shoosmith42 who used flash photolysis and
photographed Rydberg transitions in the VUV for both CH3 and CD3. Although
much of the rotational structure was diffuse due to predissociation, analysis of the
bands led to the conclusion that the methyl radical must be planar in its ground
45
electronic state.
photoelectron ;43, 44
This
finding
has
subsequently been
confirmed by
EsR,
4546 and high-resolution infrared spectroscopies.52,53
Three of the four fundamental vibrational modes are accessible by infrared
(IR) techniques. The v2 out-of-plane bending mode of CH3 was first detected in
argon and nitrogen matrices by Milligan and Jacox.49
This mode as well as the
v3 anti-symmetric stretch and the v4 in-plane bend were subsequently seen by
Snelson50 in neon-matrix spectra. Gas phase observation of v2 followed soon
afterward with the development of a rapid scan IR spectrometer by Tan, Winer
and Pimentel in 1972.51 More recently, using tunable IR laser sources, very high
resolution studies of two of the three IR active fundamentals of CH3 have been
reported. The v2 fundamental at 606.4531 cm-1 and the hot bands 2
, 1 and 3 ,
2 were observed by Yamada, Hirota and Kawaguchi using diode laser absorption
spectroscopy.52 In their study, transitions from the K=0 rotational levels for
N= odd, v2= even and N=even, v2= odd were not seen, confirming that the methyl
radical must be of D3h symmetry. Amano et al. 53 used IR difference frequency
laser spectroscopy to accurately determine the v3 band origin (3160.8212 cm-1)
and rotational constants. To our knowledge, no gas phase IR data on v4 have
been reported in the literature to confirm Snelson's neon matrix value of 1396
CM
-1
.
Of course, because of the D3h symmetry of CH3, the v1 symmetric stretch
is IR-inactive. Early attempts in the O.S.U. CARS laboratory to observe this
fundamental transition by Raman matrix isolation methods and, in 1976, in the gas
46
phase by CARS were unsuccessful. However in 1983, Harvey and Fleming were
able to detect a CARS signal for this mode in CH3 produced by 266 nm photolysis
of CH3I in a large excess of SF6, which served to thermalize the CH3 and thereby
concentrate population in fewer states.54 Subsequently, Holt et al. obtained
improved Q-branch CARS spectra of CH3 produced from the photolysis of
azomethane.55 Band contour simulations of their 0.3 cm-1 resolution spectra
yielded the origin of the transition (3004.8 cm 1) as well as the change in rotational
constants am = B0-B1 and aci = Co-C1 upon v1 excitation. More recently Kelly
has used UV resonance Raman spectroscopy to study CH3 and, although limited
in resolution, this technique has permitted the observation of v1 + 2v2 and 2v1
band contours, from which the anharmonicity constants x11 and x12 were
deduced.56
The work presented in this chapter has been a collaborative study between
the CARS groups at Oregon State and at Irvine (now Columbia). It has led to
much improved CARS v1 spectra of methyl radicals formed from the 266 nm
photolysis of CH3I, both in flow cells and in free jet expansions. Many of the N,
K Q-branch lines have been measured at high resolution and analyzed to give
accurate values for the vibrational-rotational parameters for this transition. Due
to the high density of lines and the large Doppler/collisional broadening produced
by the high dissociation velocity, the spectral analysis of the band head region is
somewhat involved. Interference between neighboring resonances can produce
significant frequency and intensity shifts in CARS spectroscopy and the effect of
47
this on the spectrum is examined.
Experimental
CARS setups of varying resolution were employed at Oregon State
University and the University of California, Irvine, in the course of these
experiments. At OSU, the primary source was a Quanta-Ray DCR-1 Nd-YAG
laser which has been retro-fitted with a Lightwave Electronics Model 6300
Injection Seeder to yield 1.06 Am radiation in 8 ns pulses with a linewidth of 55
MHz at 10 Hz. The 266 nm fourth harmonic of this laser output served as the
photolysis source while the residual second harmonic at 532 nm was partitioned
for use as the CARS pump beam and as the pump for the Stokes dye laser.
Medium resolution (0.25 cm-1) spectra were recorded using a Quanta-Ray PDL-1
dye laser as the tunable source. This laser also allowed high resolution (0.05 cm-1)
scans by insertion of a pressure-scanned etalon assembly. With nitrogen as a scan
gas, a 2 atm pressure change corresponded to an 11 cm-1 scan range at 630 nm
(DCM in dye laser). Scans with a resolution of 0.04 cm-1 were taken at Irvine
using an injection seeded Quantel 682 Nd:YAG laser and a Lumonics HD500
narrow linewidth dye laser. The very high resolution (0.005 cm-1) spectra were
obtained at OSU using a Coherent 629 cw ring dye laser and a three stage pulse
amplifier pumped by the injection seeded Nd-YAG laser. A schematic diagram
of this high resolution set up is shown in Figure 4-1. Further details on these
systems can be found in references 84 (OSU) and 85 (Irvine).
48
The very high resolution spectra were calibrated by sending a portion of the
dye output through an iodine cell and recording the absorption spectrum. The
Nd-YAG frequency is determined by the cw seed laser whose output was
temperature tuned so that the harmonic matched the 18788.445 cm-1 P53
(v' = 32,v " =0) overlapped with P103 (v' = 34,v " =0) absorption of 12.
By
monitoring the absorption of this light through a 5 cm cell, a day-to-day frequency
reproducibility of better than 0.005 cm4 was possible. Absolute values of the Nd-
YAG second harmonic to about 0.002 cm-1 were deduced from the 12 calibrated
dye output and CARS scans of known methane vibrational lines.
Both collinear and folded BOXCARS phase matching arrangements were
used in recording the CARS spectra. The UV photolysis beam was precisely
overlapped spatially with the CARS probe beams. Optical delay lines provided
for temporal delay of -1 to +21 ns of the CARS probe relative to the UV
photolysis pulse. Energies for the CARS pump, CARS Stokes and photolysis
pulses were 8-15 mJ, 1-8 mJ and 5-15 mJ, respectively. The CARS signal beam
was separated from the input beams by dichroic and color filters and
monochromators, then detected and stored by a photomultiplier, boxcar, digitizer
and microcomputer.
The methyl iodide used in these experiments was purchased from Aldrich
(99.9%) and used without further purification. The sample was delivered through
various pulsed nozzle sources in all experiments. For flowing gas conditions the
CH3I was pulsed into a small photolysis cell subject to slow exhaust through a
49
needle valve. In some experiments He or SF6 was also introduced into the cell at
flow pressures of a few to a hundred Ton so as to localize the CH3I in the focal
volume.
This sample localization reduced UV absorption and CARS signal
generation outside the focal volume.
For the supersonic jet experiments, the cell was evacuated continuously and
the jet valve was pulsed synchronously with the laser. Nozzle diameters of 0.2 to
0.5 mm were employed and the jet was probed from 1 to 15 nozzle diameters
(X/D) downstream. The CH3I sample reservoir was heatable to produce driving
pressures of 0.5 to 1 atm to achieve cooling of the parent prior to dissociation at
various positions in the jet. In some experiments, He was used as a carrier gas at
1 to 2 atm to further cool the CH3I parent. The optimum overlap of the CARS
beams was achieved by maximizing the signal of the intense CH3I band near 2971
cm-1 with no photolysis beam present.
Then the latter was introduced and
adjusted for a null in the parent intensity. A greater than 90% loss of this signal
on exposure to the 266 nm beam served to ensure nearly complete photolysis of
the CH3I in the volume probed.
Results
Figure 4-2 shows the CARS Q-branch of the parent CH3I in the symmetric
C-H stretching region, along with the rich CH3 spectrum that occurs at higher
wavenumbers on 266 nm photolysis. This result as well as those shown in Figure
4-3 were obtained by Nancy Triggs in this laboratory.87 Spectra in Figure 4-2 were
50
taken at 0.25 cm-1 resolution in a flow cell with neat CH3I at 350 Torr pulsed into
the cell maintained at about 2 Torr flow pressure. For the dominant dissociation
channel to ground state CH3 + I* (Figure 4-10), the CH3 velocity is - 4000
mis,72 implying that about 2 collisions occur in the 8 ns photolysis-probe period (if
one assumes cross sections of about 0.4 and 0.8 nm2 for CH3 and I, respectively.)
In Figure 4-3 this same spectrum is shown as trace (a), while traces (b) and
(c) illustrate the effect of increased number of collisions (-20 and 40) as
background helium was added to bring the cell pressure to 15 and 35 Torr
respectively. The observed shift of the CH3 spectrum from the band head region
near 3005 cm-1 is a clear indication of the very rapid redistribution of the high
excess translational energy of CH3 into internal rotational- vibrational degrees of
freedom. Of course collisional heating of the background gas also occurs.
Eventual cooling is seen for the methyl radical, especially when the
relaxation process is enhanced by addition of a more effective collision partner
such as SF6, as shown in traces (d) and (e) of Figure 4-3. Here a 2:1 SF6:CH3I
mix was pulsed into He background flows of 23 and 119 Torr, corresponding to
-20 and 110 collisions, respectively, assuming a cross section of 0.8 nm2 for SF6.
The increased deactivation clearly serves to reverse the intensity shift toward that
of a thermalized CH3 rotational distribution.
CARS spectra of CH3 have been recorded by Peter De Barber under
collision free conditions at Irvine.103 Figure 4-4a shows a spectrum obtained for
10% CH3I/He flowing in a cell at - 3 Ton, conditions corresponding to --
1
51
collision. Traces (b) and (c) are for CH3I cooled in a He/CH3I free jet expansion
(PTotal = 1020 Torr) at X/D = 1.5 and 7 respectively. The coupling of the parent
rotation to that of the fragment is evidenced by the shift of the CH3 spectrum
toward the bandhead as the CH3I rotational temperature is reduced. The jet
spectra also show more clearly the onset of a second band progression near 2996.5
±0.5 cm-1 which can be attributed to the v2 = 1 hot band. The frequency analysis
of the spectra in the hot band region to extract photofragment rotational and
vibrational state distributions is presented in the next chapter.
The jet results of Figure 4-4 encouraged us to record 0.005 cm-1 resolution
CARS spectra with the system at OSU in order to resolve most N, K Q-branch
features and to measure more accurate CH3 transition frequencies. Figure 4-5 is
a representative of a rich spectrum obtained at X/D= 1 for a neat expansion at 350
Torr driving pressure. In Figure 4-6 the band head region for the (1000)
(0000)
transition of this same trace is illustrated. Also displayed are calculated spectra
and assignments resulting from the analysis discussed below. Table 4-1 is a
compilation of the measured values in the 2997 to 3005 cm-1 fundamental region,
along with assignments and obs.-calc. differences. Two to five measurements were
made for most lines and the frequencies are believed to have an absolute accuracy
of 0.02 cm-1 with a relative accuracy of 0.01 cm-1. Also shown in the table are
peak x amplitudes deduced as described later for each transition considered in the
simulation of the band head region above 3000 cm-1. The analysis of the other
features seen below 2997 cm-1 required more improved experiments because of
52
extensive overlap with the (1100) 4-- (0100) hot band. This task is accomplished and
the results are discussed in the next chapter.
Analysis and Discussion
Assignments
CH3 is an oblate symmetric top for which the rotational energy levels of a given
vibrational state are represented by
Fy(N,K)=BN(N +1)+(C B)K2 DNN2(N +1)2 -DNKN(N +1)K2 -D KK4 4-1
The quantum number N characterizes the rotational angular momentum which
couples with the unpaired electron spin so that spin-rotation splittings of the levels
occur. From the work of Yamada et al.,52 these are known to be quite small,
-0.01 cm -1 for the ground state. The spin interaction was ignored in the analysis
since, for the Q-branch transitions observed here, both upper and lower levels
should be similarly shifted.
For the v1 fundamental the observed lines were fit by linear regression to
the expression
Q(N,K)= v 1+ F1(N,K) Fo(N,K)
assuming the planarity relation,5288
4-2
2DN + 3DNK + 4DK = 0. In initial
53
calculations, the parameter values of Holt et al.55 were used and assignments were
made by comparison of observed and calculated frequencies. As assignments
became more certain, transitions were added to the least squares set and the
process was repeated until almost all peaks down to 2997 cm-1 had been
accounted for. Asterisks in Table 4-1 identify a few lines which were not included
in the analysis, usually because of overlap with another transition of higher
expected intensity. The absence of K =O, N odd transitions is in accord with the
planar structure of CH3. The quality of the fit can be judged by the generally
small obs.-calc. differences shown in Table 4-1. In all, 43 transitions were fit to
obtain v1 and the differences B0-B1, etc., and twice their standard errors are
shown in Table 4-2. Also given are the resultant upper state parameters for
v1
and the other fundamentals, along with the very accurate ground state constants
of Yamada et al.52
Spectral Simulations
The relative peak CARS line intensities for the v1 Q-branch of CH3 are
given by
l(N,K)=constant[S NK( no") ]Z ,
4-3
where the line strength factor SNK includes both isotropic and anisotropic
scattering contributions. The former is a constant but the latter includes a weak
N,K dependence, which is neglected in these calculations since it is expected to be
54
extremely small for strongly polarized bands such as the symmetric CH3 stretch.
Further justification for this assumption comes from the absence of any 0 or S
branch features in the spectra, since the anisotropic contribution gives all of the
intensity of these lines.
In analyzing the intensities to deduce the rotational population distribution
of the ground vibrational state of the CH3 photofragment, the upper state
population n1NK is assumed to be zero. For a Boltzmann distribution, the relative
number density of the N, K'th level would be
noivr= (2N +1 )gNexp [ Fv(N,K)hc I k
4-4
where the nuclear spin degeneracy factor gNK is 0 (K=0, N odd), 4 (K=0, N
even), 4 (K=3p) or 2 (K=3p-±- 1).89'90 In general, significant deviations from such
a distribution were seen in the spectra, making less useful the normal comparison
of calculated and observed intensities as an aid in making N,K transition
assignments.
The instrumental width is known to be about 0.005 cm-1 for our system104
but, at the laser powers used in recording the spectra of Figure 4-6, an increase
of a factor of about 2 is estimated to arise from AC Stark and saturation
broadening.
The overall instrumental lineshape function was taken to be a
Gaussian with a FWHM value of 0.01 cm-1 and this was used in the final
convolution of I x 2 for comparison with the experimental CARS spectra. Even
though this spectral resolution is a substantial improvement over that of Figure
55
4-4, it should be noted that the measured peak linewidths for the two experimental
arrangements are not that different. This is so because collisional and Doppler
line broadening give limiting transition widths of about 0.06 cm-1.
Because of the high dissociation velocity of the CH3 fragment, both the
Doppler and collisional broadening effects are much greater than would normally
occur in a cold, low density jet. Consider first the Doppler line widths. In these
experiments, the polarizations of the nearly collinear photolysis and probe laser
beams were the same. Thus, immediately following photolysis, the CH3 velocity
component (and hence Doppler shift) will depend upon the final CH3I orientation
with respect to the probe laser propagation direction(0). The maximum shift for
CH3 fragments moving at ± 4000 m/s would be ± 0.04 cm-1, much larger than a
calculated thermal Doppler width (FWHM) of 0.01 cm-1 at 300 K. At low
photolysis levels, a broad, nongaussian lineshape is thus expected and, indeed, a
predicted 1-cos20 profile has been seen very recently by Suzuki et al.91 in their
infrared studies of v2 under collision free conditions. However, for the high,
saturating, photolysis levels used in these experiments a more isotropic distribution
can be anticipated, and such distinctive shapes should not be seen. Also, in the
jet spectra residual collisions occurring at the high gas density of the X/D = 1
sampling point used in the high resolution experiments will effect the observed
lineshapes.
A rough estimate of the number of CH3 collisions expected during the 8 ns
photolysis/probe period can be made using the common isentropic expansion
56
mode192 for a jet of neat CH3I initially at 350 Ton and 298 K.
Using the
expansion parameters of Murphy and Miller,9293 one obtains the parent density
at each centerline X/D position and this density is taken to be the same for CH3
and I*, assuming 100% photolysis. The dissociation velocities of CH3 and I* are
- 4000 and - 500 m/s and the collision cross sections are chosen to be 0.4 and 0.8
nm2 respectively. For the 8 ns interaction period, gas kinetic theory then predicts
40, 9, 4, and 2 total methyl collisions at X/D = 1, 2, 3, and 4. It should be noted
that these are maximum numbers of collisions since there is some time overlap of
photolysis and probing pulses and, in addition, the high initial CH3 velocity will
degrade due to collisions.
There is of course some uncertainty in the choice of origin for X/D; the X
= 0 distance is taken as the point at which the 0.1 mm focused laser waist strikes
the edge of the 1.0 mm thick nozzle shim (D = 0.5 mm). The sampling point of
X/D = 1 thus could really range from perhaps 0.5 to 2 or more. Nonetheless the
estimates clearly show collisions to be important at small X/D values and they
indicate that the number of collisions falls below one only at X/D greater than 6.
Thus, at X/D = 1, it is reasonable that velocity randomizing collisions would tend
to produce more Gaussian lineshapes with a full Doppler width somewhere in the
0 to 0.06 cm-1 range.
These same collisions in the jet will also produce significant Lorentzian
broadening due to dephasing effects. For strong collisions resulting in complete
loss of phase memory, the uncertainty broadening would be 0.053, 0.013, 0.005 and
57
0.003 cm"1 (FWHM) for the collision frequencies calculated at X/D = 1, 2, 3, and
4 respectively. Both broadening mechanisms are thus important but, since exact
linewidth contributions at the sampling point of these experiments are not obvious,
the experimental lineshapes for selected isolated resonances were empirically fit.
Reasonable shapes were obtained for FWHM values of 0.03 ±0.01 cm-1 for each
of the Doppler and Lorentzian contributions and these were then used in
simulating the entire spectrum.
The convolution of these gives the proper
effective linewidth of - 0.06 cm-1.
The fitting procedure involved calculating transition frequencies from
Equation 4-2 using the parameters of Table 4-2. For each transition j, an initial
xi peak amplitude was estimated from the square root of the measured peak
heights in the experimental CARS spectrum.
Each transition was given a
Lorentzian shape and both real and imaginary parts of x were then convoluted by
a Gaussian using a program adapted from that of Palmer.94 The nonresonant
susceptibility was set to zero since the lineshape simulations showed it to be
unimportant. The parts of x were then squared, added, and the result convoluted
by the Gaussian laser lineshape function using a fast Fourier transform method.
Comparison with the experimental CARS spectrum led to corrections of the xj's
and the process was iterated until the agreement was judged satisfactory.
58
Rotational Population Distribution
It should be noted that, due to interference effects between adjacent
transitions, the final peak xi's differed by up to 55% (avg. = 30%) from the initial
values estimated directly from (Ipeak-Ibase)1/2 from the experimental spectrum. This
is important since it serves as a warning that proper simulation of the spectrum
is necessary if accurate population distributions are to be extracted from CARS
data. The peak xi's are directly proportional to the 9 populations and relative
values of these are indicated in Table 4-1. Due to the residual collisions at the
sampling point in the jet, these are not nascent populations. A fit to a Boltzmann
distribution yields a rotational temperature of 540-1-90 K and a rather poor linear
relationship (R2 correlation coefficient 0.6), as seen in Figure 4-7. A calculated
spectrum at this temperature is shown at the bottom of Figure 4-6.
The population deviations are largest for high N values and for overlapping
transitions. For a given N, there is no obvious enhancement of low K levels, in
contrast to the results obtained for truly nascent products by Chandler et al. using
photoionization methods.72
These authors found that their data could be
represented by a Boltzmann factor exp[-ENK/kTN] times an extra factor exp[-
EKK/kTK] to account for the preferential production of low K states. They
obtained rotational temperatures of TN = 120 K and TK = 30 K. The higher
value of 540 K is reasonable given that collisions will rotationally excite CH3 and
blur any population irregularities.
Clearly, CARS studies under collisionless
conditions are necessary to extract the nascent populations and some such
59
improved results obtained in our laboratory will be discussed in the next chapter.
Interference Effects on Frequencies
It is interesting that, in modeling the spectra, some small systematic
frequency shifts were noted when convolving the initial "stick spectra" based on
line frequencies from Equation 4-2. Figure 4-8 shows these differences v
- v inn
for each non-overlapping N, K peak in the spectrum, where yam corresponds to
a maximum in the calculated, convoluted I x 12 spectrum. These shifts arise from
CARS interference effects between adjacent transitions and, in general, they will
differ from similar differences produced by band overlap in conventional Raman
spectra, which depend on Im x, rather than I x12.
For example, Figure 4-9 shows the Raman and CARS shifts predicted for
two adjacent Lorentzian peaks of equal intensity and linewidth (F), as a function
of separation (A/I'). For small separations, the peaks are not resolved and the
shifts (errors) are linear in separation, reaching a maximum of about 0.3 linewidth.
Note that the maxima of the Raman peaks always shift toward the mean position
of the line pair (positive shift) whereas the CARS shifts are only positive for nearly
overlapping peaks. The negative CARS shifts for larger separation result from the
dispersive shape of the real part of x, which partially cancels in the region between
the maxima. For transitions of unequal intensity, the shifts are greatest for the
weaker line.
Similar interference effects occur when the linewidths are predominantly
60
due to Doppler broadening. For CH3, the relatively large collisional and Doppler
widths enhance the interferences between the densely spaced transitions so that
there is an overall negative shift "pressure" on all transitions relative to the most
intense central region near 3002 cm-1. The least squares solid line of Figure 4-8
gives a slope of 0.01, implying that frequency corrections of about 0.02 cm-1 are
needed at the extremes of the spectra. In principle, the exact shifts should be
applied to the experimental line maxima to obtain a better measure of the true
transition frequencies and the regression procedure to extract molecular
parameters repeated. This was not done in this work because the maximum shifts
were comparable to the uncertainty of the frequency measurements and because
test calculations including the shifts gave parameters within the standard errors
discussed below.
Molecular Parameters
The molecular parameters from the analysis of the high resolution data are
shown at the top of Table 4-2 along with a comparison with the literature data.
The standard deviations given in parentheses are twice those from the least
squares fit, the increase to account for a possible absolute frequency error (for vi)
and for relative errors in the difference parameters due to interference effects.
The agreement with the CARS results of Holt et al.55 is quite good considering
the fact that their values are derived from contour fitting rather than knowledge
of precise vibrational-rotational transition frequencies. The ab initio values of
61
Botschwina et al. 57 are in only fair accord with the experimental results.
Combining the difference parameters with the ground state constants of
Yamada et al.52, one obtains the (1000) constants shown in the bottom of the
table. Also given is the available information for the other fundamental levels.
The planarity of CH3 is evident in the fact that B -=---- 2C and, for levels involving
in-plane modes, the inertial defect A = Ic - 21B is small but slightly positive, as
expected.95 The B and C values decrease slightly, by 1%, on excitation of the
symmetric C-H stretch, in accord with a larger average bond length as one moves
up the CH potential curve. From the B values R1000 is 1.0838 A, slightly larger
than the ground state value of 1.0790 A. The latter is compared with several
reference hydrocarbons in Table 4-3; the close proximity to Ro values of C2H4 and
C6H6 is consistent with the similar sp2 hybridization expected for these molecules.
The equilibrium bond length Re in the methyl radical can be calculated
from the equilibrium rotational constant, Be, given by Be = B0000 + (aBi + aB2)/2
+ aB3 + aB4. With this report of am, three of the four a values necessary to
compute Re have been determined experimentally; and for aB4, the value
calculated by Yamada et al.58 using an anharmonic potential function is taken.
The resultant Re = 1.076 A can be taken as the prototype value for an sp2
hybridized CH bond. This value is 0.010 A shorter than the spa length in
methane98 and is 0.015 A longer than the sp CH bond in acetylene.
It is interesting that the centrifugal distortion constants show a 6% decrease
when the CH symmetric stretch is excited, suggesting that the molecule is more
62
like a rigid rotor in the (1000) state. This is surprising since one might expect that
anharmonicity in the bond would make it easier to stretch, and hence to
centrifugally distort, in higher vibrational levels. However, examination of Dv
values of diatomic molecules shows a similar behavior in which Dv decreases up
to about v = 5-10 and then increases due to a higher positive term of order
(v+1/2)2. This is most likely due to limitations of the phenomenological expression
used to represent the energy levels rather than an indication of the potential
shape, since decreases in level spacings indicate that cubic anharmonic terms are
important even for v<5.
The symmetric and antisymmetric CH stretching vibrations of CH3 and
related molecules are displayed in Table 4-3, along with the weighted mean
frequencies and the CH stretching force constants. These increase with increased
s orbital participation, as expected. It is interesting that the mean frequency and
fr for CH3 are noticeably larger, and Ro shorter, than for the other sp2 cases of
ethylene and benzene. This suggests that the lone electron in the carbon pz orbital
contributes more to the CH bond strength when it is not "distorted" from its
threefold symmetry by formation of a CC pi bond.
Using the high-low frequency separation method,100 the frequencies of the
deuterated forms of methyl radical can be estimated. The results are:
CH3
3004.4 Al
3160.8 E
CH2D
2271.0 Al
3066.2 Al
3160.8 B2
CHD2
2195.0 Al
3116.9 Al
2357.5 B1
63
CD3
2125.3 Al
2357.5 E
The CD3 estimates may be compared with experimental values of 2157.5 cm-1 (A1,
cARs101) and 2381.1 cm-1 (E, diode laser absorption102).
The calculated
frequencies of the deuterated species are of course low due to anharmonicity but
the relative positions of the frequencies of the mixed isotopic species are likely to
be correct. It may be noted that these calculations predict that the symmetric Al
fundamentals of the different isotopic species are well resolved from one another,
in contrast to the antisymmetric B1 or E stretches. Thus high resolution CARS
studies of the mixed isotopes should be feasible without complications due to band
overlap, even if vibrational hot bands contribute.
The CARS data clearly show the contribution of v2 = 1 and possibly 2 hot
bands, although it is apparent that these are weaker than the ground state
transition. The data at present, particularly the jet spectra shown in Figure 4-4,
suggest that the (0100) hot band transition is at about 2996.5(5) cm-1, implying
that the anharmonicity constant X12 is -7.9(5) cm-1. This is in reasonable accord
with a value of -9.8(1.5) cm-1 obtained by Kelley and Westre57 from low resolution
resonance Raman spectra. No evidence was seen of significant population in the
(1000) state although this has been detected in some photoionization studies72 and
it is possible that the (2000) . (1000) hot band is contributing to the rich structure
in the region below 2997 cm-1. From the X11 = -22.7 cm-1 anharmonicity constant
of Kelley56, this band should be below 2982 cm-1. A more detailed analysis of this
region requires better frequency measurements and such results obtained with new
64
improvements in the O.S.U. CARS setup are discussed in the next chapter.
Summary
Methyl radical was formed via the 266 nm photolysis of CH3I and CARS
spectra of the symmetric stretching mode were obtained under a range of
experimental conditions. Quasi-static cell measurements with added buffer gases
showed the rapid conversion of the high initial kinetic energy of CH3 into
rotational energy, with ultimate thermalization to a Boltzmann population
distribution after about 100 collisions. Jet spectra at medium resolution gave
simpler spectra due to the cooler parent and to the reduced number of collisions
in the expansion region. Spectra at 0.005 cm-1 resolution near the nozzle showed
that, despite appreciable Doppler and collisional broadening due to the high recoil
velocity of the CH3 fragment, most N, K vibrational-rotational Q-branch transitions
were resolved. Even at this high resolution such broadening of the transitions lead
to interference effects among the closely spaced Raman transitions that influenced
both the line positions and intensities in the observed CARS spectra. Procedures
for extraction of accurate rotational populations were developed and the transition
frequencies in the band head region were analyzed to obtain the molecular
parameters: v1 = 3004.418(34), _a Bi = 0.04753(70),
aci = 0.04753(70), DN1 -DNO
= -0.000046(8), DNK1 -DNKO = 0.000083(20) and DK1 -DK0 = -0.000039. These
results and infrared data in the literature yield a CH bond length of 1.08378(5) A
for the (1000) state and, with some assumptions, an equilibrium bond length Re
65
of 1.076 A for this prototypic case of sp2 bonding. These studies show that the
resolution, sensitivity, and short probe period of CARS can be quite advantageous
in the investigations of short-lived transient species.
66
Table 4-1. u1 Q-branch transition frequencies for CH3 (cm-1)
N
*
K
Obs.
Obs.-
X
Ca lc.
Ca lc.
N
K
Obs.
Obs.-
X
Ca lc.
Ca lc.
0
0
3004.423
0.007
0.155
8
8 3000.690
-0.022
0.511
1
1
3004.284
0.000
0.216
7
5 3000.646
0.003
0.293
2
2
3004.059
0.002
0.327
7
4 3000.347
0.015
0.282
2
1
3003.936
-0.009*
0.322
8
7 3000.207
0.036
2
0
3003.922
0.014
0.728
7
3 3000.117
0.021
3
3
3003.721
-0.014
0.969
7
2 2999.950
0.021
3
2
3003.547
-0.002
0.528
9
9 2999.824
-0.003*
3
1
3003.439
0.000
0.438
7
1
2999.824
-0.006
4
4
3003.308
-0.009
0.623
8
6 2999.698
-0.019
4
3
3003.066
0.006
0.857
8
5
2999.333
-0.010
4
2
3002.892
0.014
0.350
9
8
2999.230
0.012
5
5
3002.807
0.000
0.722
8
4 2999.030
-0.015
4
1
3002.756
-0.013*
0.561
10
10
2998.831
-0.019*
4
0
3002.721
-0.013
0.864
8
3
2998.831
0.014
5
4
3002.468
-0.009
0.533
8
2 2998.645
-0.012
5
3
3002.227
0.003
0.623
8
1
6
6
3002.185
-0.017
0.850
8
0 2998.540
0.010
5
2
3002.044
-0.002
0.512
9
6 2998.220
-0.046
5
1
3001.940
-0.001
0.614
9
5
2997.875
-0.034
6
5
3001.789
-0.012
0.696
11
11
2997.798
0.017
7
7
3001.487
-0.016*
9
4 2997.708
6
4
3001.487
0.008
1.000
10
8 2997.588
6
3
3001.245
0.011
0.828
9
3 2997.387
-0.020
6
2
3001.059
-0.003
0.544
9
2 2997.255
0.001
7
6
3001.059
0.027*
0.834
9
1
2997.189
0.027
6
1
3000.927
-0.031*
0.745
10
7 2997.121
-0.011
6
0
3000.927
0.003
0.312
2998.540
indicates lines not used in linear regression analysis
M.022*
0.085*
0.007*
Table 4-2. Vibrational-rotational parameters for CH3 (cm 1)
v
aB
aC
DNO-DN1
DNKO-DNK1
CARS
This Work
3004.417(34)
0.08510(78)
0.04753(70)
-0.000046(8)
0.000083(20)
(-0.000039)
CARS
Ref. 14
3004.8(2)
0.085(2)
0.048(2)
LEVEL
0000
1000
REF.
14
This Work
v
as
ac
B
C
e(amu A2)
DN
DNK
DK
R(A)
9.57789
4.74202
0.03490
0.000770
-0.001358
0.000634
1.07895
3004.417
0.08510
0.04753
9.49279
4.69449
0.03928
0.000816
-0.001441
0.000673
1.08378
Ref. 16
3067
0.092
0.044
0100
0010
0001
15
a
3160.8212
1396
0.10679
(-0.25397)
0.04035
9.47110
(9.83186)
4.70167
-0.13823
0.02562
0.004940
0.000759
-0.000706
-0.001366
0.000282
0.000637
1.09743
1.08502
(1.0624234
14
606.4531
0.31975
-0.06962
9.25814
4.81164
Equil
b
9.63313
1.07585
a. v4 value is Ne matrix value from Ref. 50. Values in parantheses derive from aB value calculated by Hirota
and Yamada, Ref. 58.
b. Be = B0000 + (aBl
aB2)/2 aB3
aB4
68
Table 4-3. Molecular parameters for CH3 and related molecule.a
spa
sp2
Sp
a
Ro
v sym
v asym
v mean
fr
A
cm-1
cm-1
cm-1
mdyn/A
CH4
1.0940
2917
3019
2994
5.04
CH3
1.0790
3004.4
3160.8
3109
5.30
C2H4
1.086
3026,2989
3130,3106
3056
5.08
C 6H6
1.084
3062,3068
3063,3047
3058
5.15
C2H2
1.058
3374
3289
3332
5.92
Except for CH3, R0 and 4. are from Refs. 48, 55, v's from Ref. 56.
69
Single-mode
Ar+ laser
ring dye laser
II
t,
II
spatial
filter
12 filter
CD
Sample
cell
Monochromator
c)
266nm
532nm
A
dye
Seeded
Single-mode
Nd:YAG laser
CD
0
Dye amplifier chain
Figure 4-1. O.S.U. high resolution CARS experimental setup.
70
1
2965
2975
i
2985
2995
WAVENUMBERS
1
3005
Figure 4-2. CARS Q-branch spectra of CH3I (bottom trace, uv off) and CH3
produced by 266 nm photolysis.
71
E
(q
2965
2975
2985
2995
WAVENUMBERS
3005
Figure 4-3. Static cell spectra of the Q-branch structure of CH3 produced by
photolysis of CH3I at various pressures.
72
P (TORR)
STATIC
3
i
\A
P. (TORR)
XID
1020
1.5
1020
7
A .
JET
11111111111111111
2990
2995
3000
3005
WAVENUMBERS
Figure 4-4. CARS spectra of CH3 produced by photolysis of 10% CH3I in He.
73
2992
1111111111111
2994
2996
2998
3000
3002
3004
3006
WAVENUMBERS
Figure 4-5. High resolution CARS spectrum of CH3 produced by 266 nm
photolysis at X/D = 1 in a jet expansion of neat CH3I at 0.5 atm.
74
=N
IIIII
K= 02 4
I
I
6
II
I
I
15
Ill
14
I
It
1113
in 2
I
OBS.
110
1
I
j
\
lki
CALC.
AA
CALC.: T
rov
uu
ROT
l.)
11
J
\./
= 540 K
,JuAk W
3001
3002
3003
3004
WAVENUMBERS
Figure 4-6. High resolution CARS spectra of CH3, top trace is the first
portion of the spectrum shown in Fig. 4-5, middle trace is a simulated
spectrum and the bottom trace is a calculated spectrum with an asuumed
T= 540 K.
75
0
200
400
E(NK)/Ic
600
(K)
Figure 4-7. Boltzmann fit of CH3 CARS spectrum of Fig. 4-6. The N quantum
numbers are shown, with implied K values decreasing from left to right.
76
0.02
1
I
I
0.01
I
I
6
I
0.00
I
I
I
g
I
-0.01
I
-0.02
3001
3002
3003
3004
WAVENUMBERS
Figure 4-8. Line shifts of calculated transitions (stick spectrum) produced by
linewidth convolutions. See text for discussion.
77
0
5
10
A/r
Figure 4-9. Comparison of Raman and CARS line shifts (in units of F) produced
by two adjacent Lorentzian lines of equal intensity.
78
i
\ - I/
C
I .0° i + C
'66
NN I
73%
I'
+C
27%
II
CH3 I Potential Energy Diagram
25
20
5
0
i
I
:1
r
C-I
6
(A )
Figure 4-10. Potential energy diagrams for CH3I (bottom)
photodissociation pathways for CH3I photolysis at 266 nm (top).
and
79
CHAPTER V
266 nm CH3I PHOTODISSOCIATION: CH3 SPECTRA AND POPULATION
DISTRIBUTIONS BY COHERENT RAMAN SPECTROSCOPY
Introduction
Due to it's appeal as a prototype for polyatomic photofragmentation, CH3I has
been the target of numerous experimental and theoretical studies in the past
It is well known that U.V. absorption of CH3I in the
couple of decades.
wavelength region from 360 to 200 nm produces methyl radical via two exit
channels, one involving dissociation to CH3 + I(2P3/2), the other to CH3 +
I*(2Pia).115 Evidence that the iodine photoproduct was mostly generated in the
latter population-inverted state led to an early focus on the use of alkyl iodides for
photodissociation lasers, as first reported by Kasper and Pimentel in 1964.64 From
techniques such as time of flight (TOF) mass spectrometry,6745 resonance
enhanced multiphoton ionization (REMPI),71,73, 116 infrared fluorescence109'75 and
absorption91'76 spectroscopies, and U.V. emission spectroscopy,8 1 the I*/I
branching ratio is now reasonably well-determined for various photolysis
*
wavelengths. Both I and I fragments originate from a parallel (300,1A1 ; a ,n)
80
transition. At 266 nm, Riley and Wilson65 and Hess et al.124 have shown that
about 75% of the iodine atoms are generated via the spin-orbit excited I* channel
which correlates to the 3Q0 state. The ground state I atom correlates to a 1Q1
excited state which is apparently accessed by a curve crossing with 3Q0 at a C-I
bond distance of 2.4 A,117 about 0.3 A longer than that at the instant of absorption.
Amatatsu et al.117 describe the potential surface at this intersection point and give
a good survey of earlier experimental and theoretical work.
Because of the common 3-fold symmetry of the excited electronic state of
CH3I and the CH3 product, the system has often been modelled as a pseudo
linear triatomic system, with all three hydrogen atoms regarded as one atom. A
more realistic, but still simple, model allows internal excitation of those vibrational
modes of CH3 which retain the three-fold symmetry of the dissociation process.
This implies that only the A, 1 symmetric CH3 stretch (u1) and the A"2 out-ofplane bend (u2) might be excited in the CH3 product. Since the CH3 group goes
from a pyramidal to planar configuration along the dissociation coordinate, it
would be expected that excitation of the u2 umbrella mode would be most likely.
However, measurements of the distribution in this mode have given conflicting
results (Table 5-1). Sparks et al.67 first found by a TOF experiment of the 266 nm
photodissociation of CH3I that the distribution peaked at v2 = 2 for the I* and at
v2 = 4 for the I channels respectively. Van Veen et al.69 and Barry et al.68
subsequently deduced similar inverted population distributions at 248 nm. These
81
TOF measurements were limited in resolution and the results had a large
uncertainty. However, Hermann et al.75 also obtained inverted v2 vibrational
distributions from a fit of broad infrared emission spectra and reported up to 10
quanta of excitation in the umbrella mode with the peak of excitation at v2
for both
248
and
266
= 2
nm photolysis. These experimental results were supported
by the theoretical calculations of Shapiro et al.60, who assumed a linear
pseudo-triatomic model for CH3I and predicted distribution peaks at v2
5 for
266
= 2
and
and 248 nm photolysis respectively.
More recent resonant ionization TOF measurements71'73'116 indicate a
quite different distribution. For example, Loo et al.71 deduced nearly equal
populations in the v2
al.72
= 0,1,2
states of CH3 produced at
266
nm and Chandler et
saw evidence of some v1 = 1 product. Although quantitative estimates from
these and other REMPI results may be subject to question due to uncertainties in
the intensity factors for the excitation and ionization steps in the experiment71, a
non-inverted v2 vibrational distribution was also reported by Suzuki et al.91 for 248
nm products probed by direct infrared absorption. This latter method was again
used in the studies of Hall et al.76 where a similar distribution was deduced for
CD3 products formed at 248 nm.76 Also recent theoretical trajectory calculations
using an ab initio potential energy surface117 have given distributions which are in
good agreement with the results of Suzuki and Hall. Finally we note that a noninverted distribution was evident in our recent study of the u1 symmetric stretching
82
mode of CH3 by coherent anti-Stokes Raman spectroscopy (CARS).105
The rotational distribution of nascent CH3 has also been of interest but has
been less studied since rotationally-resolved spectra have been hard to obtain.
Sparks et al.67 found that a 300 cm-1 wide rotational distribution (Trot - 290 K)
gave the best fit to their broad TOF data. In similar experiments, Loo et al.71
were able to resolve some rotational structure and deduced a rotational
temperature of 120 ± 30 K for the CH3 v2 = 0 state, with an indication of some
excess K = 0 rotational population. Such an excess was also seen by Chandler et
al.72 and they found their spectra were best fit using two rotational temperatures
TN = 120 K and TK = 30 K. These experiments are in accord with the recent
calculations of Amatatsu et al.117, which predict an increase of only one unit of
angular momentum when the cold parent dissociates via the I* channel. However,
for warmer parent such as the room temperature effusive beam experiments of
Black and Powis116, a preference for K = ± N products was seen and the
rotational temperature of CH3 (200 K) was colder than that of CH3I.
In none of these studies of nascent CH3 product distributions were
individual N, K transitions resolved and the populations deduced involved a rather
complex simulation procedure as discussed by Loo et al.71 In the present work,
such detail has been seen in the vibrational-rotational spectrum of CH3 using an
improved high resolution CARS apparatus. By use of supersonic expansions of
CH3I with various driving gases, and by photolyzing and probing at different
83
positions in the expansion, spectra are obtained under a variety of collision
conditions. Extensive rotational excitation of the CH3 product is seen after a few
collisions and the rich structure is partially analyzed to give improved vibrational-
rotational parameters for the (1000,-0000) fundamental and the (11004-0100) hot
band transitions. Spectra were also obtained under near-nascent conditions and
the analysis to deduce vibrational-rotational population distributions is presented
and discussed.
Experimental
The CARS experimental setup84,105 at Oregon State University has recently been
modified for high resolution studies by addition of a novel long-pulse injectionseeded Nd:YAG pump laser. This laser (custom made by Continuum) is special
in that it provides single frequency 532 nm pulses of -45 ns duration (FWHM)
with up to 200 mJ of energy. It consists of a 2 m stable TEM00 oscillator followed
by two amplifier stages, with seeding for single frequency output achieved by
injection of -9 mW of cw output from a diode-pumped Nd:YAG laser (Lightwave
Electronics seeder, model 122-1064-50F). A piezoelectric driver for the oscillator
end mirror is controlled by electronics to ensure the stability of the cavity length
at a resonant frequency determined by the temperature of the seed laser. For
some experiments, a short cavity oscillator modification (0.75 m) was used for
shorter pulses (-10 ns) of higher peak power (-5x), yielding significantly increased
84
CARS signals. More details about the characteristics of the system are given in
reference 106.
The above laser served as both a CARS pump source and a pulsed
amplifier pump for the Stokes beam derived from a cw ring dye laser (Coherent
629). The latter laser was excited by an Ar+ laser (6-7 W) and the dye laser was
operated with a dye mixture (Exciton DCM mixed with Kiton red) optimized to
providing 200-500 mW of power at -630 nm. This cw output was pulse amplified
in four stages to give a maximum gain factor of -106. Typical powers for the
pump, and Stokes pulses were 20-30 and 5-10 mJ per pulse respectively. For 0 ns
second U.V. delay experiments, the 532 nm YAG laser beam was frequency
doubled using a KDP* crystal and the doubled light at 266 nm served as the
photolysis source. For experiments with longer U.V. delays (0-3 ms) a separate
Cooper LaserSonics MY-118 Nd:YAG laser was used to generate the 266 nm
pulse.
For the 02 frequency calibration, part of the dye laser beam was sent
through an iodine cell at -40 °C and an absorption spectrum was recorded
simultaneously with the CARS spectrum. For the ca YAG laser frequency
calibration the seed laser was temperature tuned to 18788.4624(7) cm-1, 106 which
corresponds to the 50% transmission point (high frequency side) of the 12 Atlas32
line number 1111 near the YAG laser gain maximum. A computer was used to
actively lock the seed laser to this frequency to correct for drift due to
85
temperature instabilities of the temperature control electronics. The absolute
uncertainty of the Raman shift frequencies (col - 6)2) is estimated to be less than
0.02 cm-1 and, from standard deviations of relative shift values of four or more
measurements, the relative CH3 frequencies are believed accurate to 0.006 cm-1.
All of the experiments were done under supersonic jet expansion
conditions. For this purpose the methyl iodide precursor (99.9% Aldrich) at -350
Torr was pulsed into a cell pumped to maintain a background pressure of 100-500
mTorr. The pulsed nozzle valve was synchronized with the pump and photolysis
lasers for suitable time overlap of the beams and the molecular beam. Mixtures
using rare gases or ethane as driving sources at pressures of 1-7 atm were made
by bubbling these through CH3I liquid contained in a metal vessel at room
temperature. Nozzle diameters (D) of 0.9 and 1 mm were used and the molecular
beam was probed at X/D positions of 0.1 to 11 in the jet.
At higher driving
pressures some clustering to form dimer and higher aggregates of methyl iodide
would be expected but no indication of such species was seen in scans of the
spectral region of liquid and solid methyl iodide (2946-2960).107 Thus most of the
CH3 product observed is believed to derive from photolysis of monomeric CH3I.
The folded BOXCARS phase matching technique was used, with beams
focussed to -0.1 mm diameters with a 400 mm focal length lens aligned by
optimizing a strong CH3I CARS signal at 2971.2 cm-1. The U.V. beam focal
diameter was larger (-0.20 mm) and, when aligned, gave >95% reduction of the
86
parent signal. All polarizations were parallel for maximum CARS signal and
rotation of the U.V. polarization had little effect, indicating saturation of the U.V.
absorption. Some effort was made to study alignment effects of the CH3 product
at reduced U.V. powers but the lower CARS signals then seen for CH3 made the
results inconclusive. Similarly at large X/D distances in the expansion, where the
CH3 products are nascent, the CARS signals were quite low due to the low
number density. To improve the signal to noise the short cavity mode of the
Nd:YAG laser was used, resulting in a signal gain of about 100. Under these
conditions some power broadening of CH3I parent Q-branch was seen due to AC
Stark shifts and saturation broadening. This effect was not obvious for CH3 due
to the broader Doppler profiles of the radical so that the CH3 distributions
deduced from peak areas are believed to be reasonably accurate (-10-20 %).
Results
Figure 5-1 displays a representative CARS spectrum of the methyl radical
Q-branch structure in the u1 symmetric stretching region and shows the richness
of the spectrum after many collisions have occurred. This trace was obtained in
a jet by driving the CH3I at 298 K and 350 Torr with 2 atm of argon and by
photolyzing and probing the radicals without delay at X/D = 1 along the expansion
axis.
The Q-branch origin starts at -3004.5 cm -1 and the rotational structure
extends about 35 cm-1 to the parent CH3I region near -2971 cm-1. The CH3I
87
Q-branch peaks observed in this latter region are about 10 % of the intensity seen
prior to introducing the 266 nm U.V. photolysis beam.
Indicated on the top portion of Figure 5-1 are the N, K assignments for the
v1 fundamental Q-branch transitions. These assignments are based on our earlier
study105 of this mode and are extended here to include part of the overlap region
with the hot band transitions. Table 5-2 contains the observed frequencies of all
assigned lines as well as the obs.-calc. differences for each transition. Also given
in the table are the relative CARS intensities obtained from simulations of the
spectrum of Figure 5-1. For rotationally hot CH3 products many transitions were
seen below -2997 cm-1 where overlap with vibrational hot bands in v2 and v1
might be expected. Some were assignable to the v2 = 1 hot band (Table 5-2) but
many others remain as yet unassigned. Table 5-3 is a compilation of these
unassigned but reproducible features, along with the relative intensities
corresponding to Figure 5-1. All frequencies in Tables 2 and 3 are the average
value of at least four measurements with standard deviations averaging 0.006 cm-1.
The details of the spectral analysis are given in the discussion section.
In figure 2 a series of CARS Q-branch jet spectra illustrate the rotational
heating caused by increasing number of collisions of CH3 with other CH3 radicals,
with I atoms, and with helium. Collision numbers are deduced by using the
isentropic expansion mode192 for a jet to calculate the local translational
temperature and number density at each X/D position. The photolysis was
88
assumed to be 100 % efficient so that CH3 and I densities are those of the parent
CH3I.
Gas kinetic theory then was used to calculate the number of collisions
during the photolysis-probe period, assuming collisional diameters which are listed
in Table 5-6, along with the results and the experimental conditions for the
spectra. It should be noted that this calculation also requires an estimate of the
relative collision velocities, a point we return to later.
The top trace (a) of Figure 5-2 is a jet spectrum at X/D = 8 with helium
driving pressure of 4 atm. These conditions correspond to a near-nascent
distribution for which a Boltzmann temperature of 230 K is deduced as described
in a following section. As the number of collisions increases, traces (a-e), the
rotational distribution clearly shifts away from the band origin as higher N and K
states become populated. The translational to rotational (T-- R) energy transfer
results in an increase in the rotational temperature from 230 K in trace (a) to a
maximum of about 1160 K in trace (d). With further collisions, the distribution
shifts back towards the band origin in trace (e) and the lower Boltzmann
temperature of -930 K for this case suggests a nearly thermalized sample.
In several experiments N2 was used as the driving gas and the lowfrequency pure rotational region was scanned in an attempt to directly monitor the
rotational distributions of both CH3 and N2 as a function of collision number.
Extensive pumping of N2 population from low to high rotational levels was seen
after a few collisions but no features attributable to CH3 were detected.108 Since
89
good spectra were obtained for CH3I parent molecule, the low apparent intensity
of the CH3 radical suggests that the rotational Raman cross section, and hence the
polarizability anisotropy, of CH3 is quite low.
Analysis and Discussion
Spectral Analysis
For an oblate symmetric top the rotational energy level expression for each
vibrational state is given as
F(N,K) = BN(N+ 1) + (C-B)K2 - DNN2(N+ 1)2 - DNKN(N+1)K2 - DKK4
+ HNN3(N+ 1)3 + HNKN2(N+1)2K2 + HKNN(N+1)K4 + HKK6
(1)
where the N quantum number characterizes the total rotational angular
momentum while K determines its component along the 3-fold symmetry axis. B
and C are the usual rotational constants while the D and H parameters are
centrifugal distortion constants. No effects of electron spin are included since the
level splitting caused by this is known to be quite small (0.01 cm-1 or less)52 and
to essentially cancel for Q-branch transitions in which AN and AK = 0. These
transitions occur at frequencies given by
90
QNK = u + F1(1`1,1()
Fig(N,K)
(2)
where u is the band origin and and refer to upper and lower vibrational states
respectively. This expression, without H's, was used in our earlier analysis of this
band105 but, in the present work, the increased frequency accuracy and extension
to higher NK values required inclusion of the H constants for a satisfactory fit.
Table 5-2 contains the obs.-calc. differences obtained with and without the H
parameters and it is clear that they are important in fitting the high NK transitions.
However, in general these H's are not well determined since they depend critically
on high NK transitions, of which only a few could be assigned confidently due to
the complexity of the spectrum below -2997 cm-1.
From the analysis of the rotational structure of the u1 fundamental of CH3,
it is clear that many of the lines below 2997 cm-1 must be assigned to one or more
vibrational hot bands. This is especially evident in the cold, near-nascent spectra
shown in Figure 5-2 (a) and (b), where the onset of a separate band system
attributed to a v2 = 1 starting level is seen. With increasing number of collisions,
higher NK lines of the fundamental overlap the hot band region and this made
identification of the hot band features difficult. Nonetheless, by examining the
intensity changes and positions of the features below 2997 cm-1 for different
expansion conditions, it was possible to assign a limited number of the transitions
to the hot band. These are listed in the bottom of Table 5-2 along with relative
91
intensities corresponding to the spectrum of Figure 5-1.
Since only low NK
transitions are assigned, the higher order H centrifugal distortion constants were
omitted in fitting these hot band data to Equation 2. In addition, the planarity
condition 2DN + 3DNK + 4DK = 0 52 was assumed to reduce the number of
fitting parameters.
Given in Table 5-4 are the new vibrational-rotational u parameters for
both the v2 = 0 fundamental and v2 = 1 hot band, along with molecular constants
calculated for the upper states using the lower state values of Yamada et al.52 For
both transitions, the B value decreases about 0.09 cm-1 on excitation of the 01 CH
stretch by one quantum, corresponding to an average bond length increase of
0.005 A. These and other parameter values for the fundamental transition fall
within the uncertainties of our earlier measurements105 and the comparisons
offered there with similar molecules remain valid. From our frequency of the hot
band origin 2996.21(4) cm-1, we deduce a value of -8.23(5) cm-1 for the x12
anharmonicity constant. This value is in reasonable agreement with a value of
-9.8(1.5) cm-1 estimated by Kelly et al.56 from their low resolution resonant
Raman spectra of CH3. This x12 value serves as the basis for predicting the band
origins of higher overtones of 02, as indicated in Figure 5-1. Also shown there is
the origin of the vi = 1 hot band predicted from the approximate x11 value of
-22.7 cm-1 reported by Kelly et al.56 Some structure is seen near these origin
positions in Figure 5-1, but we note that no strong features were observed below
92
2990 cm-1 for scans corresponding to near-nascent products (Figure 5-2a, b and
others). It is of course possible that higher vibrational levels are excited due to
an increase in the number of collisions occurring under the conditions for Figure
5-1 and Figure 5-2 c-e, a point we consider below.
Collision Numbers
One would like to relate the spectral changes seen in Figure 5-2 a-e to the
number of collisions experienced by a CH3 with another species during the
photolysis-probe period At. From simple gas kinetic theory, this is given by
nCH3...X = crel ir [(dcH3 + dx)/2] 1/2
Here crel = [c2cH3
c2x ,i i/2,
Nx At
(3)
Nx is the number density in the jet, and At is taken
as the half width of the undelayed 532 nm CARS pump beam. The initial
velocities of CH3 and I are about 4000 and 500 m/s respectively72 while that of
the driving gas is
eX = [8RThrm] 1/2
(4)
where T is the local translational temperature in the jet and M is the average
molecular weight of the expansion mixture. Use of the initial velocities for CH3
93
and I gives total collision numbers of 7 and 17 for our nearly collision free
conditions, X/D = 8 and 5 (Figure 5-2a, b). However, these are clearly too high
since, for the first few successive direct CH3He collisions, momentum-energy
conservation indicates that the CH3 velocity drops nearly by half each time.
Taking this into account, we estimate that more realistic values are -3 and -6
collisions at these two X/D positions. At higher jet densities, the CH3 experiences
even more collisions and it can be expected that the CH3, I, and background gas
in the photolysis volume will reach some sort of thermal equilibrium in the
translational energy. One would expect this effective translation temperature to
be higher than the local isentropic jet temperature due to the photolysis heat input
but a direct measure of Ttrans is not available. Eventually this should equate to
the internal rotational temperature of the CH3 radical which we can deduce from
the CARS spectra, as outlined later. Accordingly, we have used these Trot values
in Equation 4 to estimate CH3 velocities and hence average collision numbers for
the cases listed in Table 5-5. The exceptions in this table are the X/D = 8 and 5
instances in He expansions where this approach gives values of 1 and 4
respectively, somewhat lower than the -3 and -6 values we believe to be more
realistic.
94
Vibrational Population Distribution
Since translational to vibrational (T -*V) energy conversion usually requires
many collisions, the CARS spectra obtained under low density cold conditions give
access to the nascent vibrational populations. To deduce these distributions, four
cold jet spectra such as those shown in Figure 5-2 (a) and (b), were chosen since
in these there were no overlapping rotational peaks between the fundamental and
the hot band transitions. After proper baseline subtraction, the square root of the
CARS signal intensities was taken to give peaks which are essentially proportional
to the populations of each individual NK state. The area under the fundamental
band from 3005 to 2997 cm -1 and that for the hot band from 2997 to 2985 cm-1
was then obtained by integration and an average ratio of the relative v2 = 0 : v2
= 1 populations was found to be 1.00:0.27(10). The uncertainty is relatively large
due to the low S/N for these spectra, however the result is consistent with the
more recent, non-inverted experimental distributions noted in Table 5-1 and is in
good accord with the theoretical ratio deduced by Amatatsu et al.117 Amatatsu
et al. also predict a low relative v2 = 2 population (0.09), about one third of that
of the v2 = 1 product. Since the CARS signals scale as number density squared,
our S/N would be marginal for detecting such a low relative concentration and it
is not surprising that in scans under near-nascent conditions, we were unable to
discern any CH3 feature in the v2 > 1 region.
However under higher density conditions involving more collisions, extensive
95
structure appeared in the hot band region, as can be seen in Figure 5-1 and Figure
5-2 c-d. Most of this is attributed to T-'R collisional heating rather than T--,V
excitation, based on the relatively low number of collisions occurring for most of
our sampling conditions compared to common V--0T/R collision numbers. For
example the 711 cm-1 u5 bending mode of acetylene requires -1100 collisions for
deactivation in neat samples and this increases to 22,000 and 15,600 in Ne and
Ar.121
Comparable numbers might be expected for the u2 mode of CH3 at 606
cm-1 and even larger values for the other CH3 modes of higher frequency. Since
only about 50 collisions have occurred for the sample whose spectrum is displayed
in Figure 5-1, little vibrational excitation is expected and most of this structure
must come from rotational excitation of the nascent vibrational distribution. It
might be argued that the first few high velocity CH3X collisions could be
especially effective in producing vibrational excitation but the nearly constant v2
= 0 : v2 = 1 intensity ratio seen in Figure 5-2a and b argues against this. Finally,
we note that, after -6300 collisions (Figure 5-2e) where rotational-translational
equilibrium is likely to have occurred, no indication of excess v2 = 1 (or higher)
population was seen. Thus we believe the nascent vibrational distribution is frozen
during the time periods for our measurements and that the complexity of the
region below 2997 cm-1 comes from collisional excitation of the high NK rotational
states of the v2 = 0 and 1 vibrational levels.
96
Spectral Simulations
To extract accurate relative rotational populations it was necessary to
simulate the CARS spectra as discussed in Ref. 2. The relative intensities of the
CARS Q-branch lines are, to a good approximation, proportional to the square of
the population n"(N,K) of the lower vibrational state
n"(N,K) = (2N+1) g"NK exp[-F"(N,K)hc/kT]
(5)
For the A"1 v2 = 0 levels with K = 0, the nuclear spin factor gNK = 0 for Nodd,
4 for Neven while for the A2 v2 = 1 level gNK = 0 for Neven, 4 for Nodd. For all
levels with K o 0, gNK is 4 (K = 3p) or 2 (K = 3p ± 1) where p is an integer.
The simulation involved an iterative procedure in which the square root of
a measured CARS peak intensity was taken to give an initial estimate of xNK nNK
INK112*
Line width parameters were chosen empirically to reproduce the
shapes of isolated lines. A Lorentzian width of 0.05 cm-1 (FWHM) was used to
account for natural width and collisional-broadening and the real and imaginary
parts of x were then Doppler-broadened by a Gaussian line shape (FWHM = 0.03
cm-1) using a CARS program derived from that of Palmer.94 The two parts of x
were squared and summed and, to account for the contribution of the laser widths,
the result was convoluted by a Gaussian line shape function (FWHM = 0.006 cm-
97
1). Further small refinements of the peak xNK values were then made to account
for interference effects between neighboring peaks until a good visual fit of all
features in the spectrum was achieved. In general the final peak intensities
differed by no more than 12% (avg. 5%) from the original observed intensities.
Figure 5-3 shows a comparison between observed and calculated spectra
for CH3 obtained under near nascent conditions [(350 Torr CH3I with 4 atm He
driving gas and at X/D = 8 (trace a) and 5 (trace c)]. Here some of the weaker
NK transitions were not included in the simulation but the overall quality of the
fit is considered good and the relative populations are believed to be accurate to
about 10 to 20%.
Rotational Temperatures
The relative rotational populations deduced from the simulations of each
spectrum were then fit to extract a corresponding Boltzmann rotational
temperature. This of course is not expected to precisely characterize the true
population distribution but it does serve to provide a rough measure of this in
terms of a single parameter. A representative Boltzmann fit is shown in Figure
5-4 for the near-nascent spectrum of Figure 5-3a (-3 collisions) and a rotational
temperature of 230(40) K is obtained. A similar fit of trace c (-6 collisions) of
Figure 5-3 results in a somewhat higher temperature of 1180(50) K. Table 5-5
gives Trot values obtained for a variety of other expansion mixtures where more
98
collisions and higher rotational temperatures were observed.
Figure 5-5
summarizes the variation in Trot with total number of collisions, most of which are
with the driving gas.
Although qualitative, the figure clearly suggests little
difference in T R conversion efficiency among the inert gas collision partners.
For these, maximum heating to -1100 K occurs after -100 collisions and then
cooling occurs as the radical becomes thermalized. Ethane was used as the
collision partner in a few experiments and, from the figure, it is clear that is more
efficient in accepting the collisional energy due to the many internal vibrational
degrees of freedom available to it.
At very low driving pressures or at large X/D values, the collision-free limit
is reached but we were unable to achieve this extreme due to low S/N in our
current experiments. However, Chandler et a172 and Loo et al.71 have obtained
a value of 120 K in their photoionization studies under cold, nascent conditions
and we show this limit in the figure.
v2 = 0 Rotational Distribution
A more detailed measure of the rotational distributions obtained for
near-nascent condition is given in Table 5-6. A visual comparison with the
corresponding Boltzmann population is offered in Figure 5-6 where the N
populations for each K value are grouped together.
In some cases, the
experimental values are for overlapping peaks and here the NK assignments of
99
other contributing lines are shown above the bars and the predicted Boltzmann
results are summed.
In general the deviations from Boltzmann population distributions are
surprisingly small, given the near-nascent experimental conditions. Little change
occurs in the distributions we obtain for -3 vs -6 collisions, the principal
difference being a slight increase in relative intensity for the higher N lines for
each K value. It is perhaps noteworthy that the (non-overlapped) low K states
have populations somewhat larger than Boltzmann while for K = 3 and higher this
trend reverses. This enhancement of the low K states is consistent with the
findings of Loo et al.71 and with the photofragment imaging results of Chandler
et al.72, both of which were obtained under truly nascent conditions. Although no
K structure was actually resolved in the latter study, some relative N,K populations
were extracted from spectral simulations and we list these results also in Table 5-6.
Figure 5-7 gives a visual comparison of the relative populations for those states
which were seen in both studies and which were not involved in overlapping CARS
transitions. Not surprisingly this comparison shows that, as the nascent fragments
undergo an increasing number of collisions, the higher N and K levels are
increasingly populated.
100
K Conservation
In part, the comparison of Figure 5-7 is misleading since the initial
rotational distribution of the parent CH3I is also expected to influence the final
product distributions. An important aspect of the dissociation dynamics of the
methyl iodide is the retention of the molecular symmetry axis in forming CH3.
This implies that the repulsive forces causing dissociation in the excited CH3I
molecule must be directed along the symmetry axis. In this simple picture, no
torque is exerted around this axis, and there would be no rotational excitation of
the photoproducts about the symmetry axis of the molecule. This in turn implies
that the K quantum number characterizing spin about the figure axis must be
preserved in the dissociation process.
To examine the validity of this prediction an analysis was made for the
population distributions of the rotational K states of the parent CH3I and CH3
under the same experimental conditions. A representative Q-branch spectrum of
neat CH3I in a jet at X/D = 6 is shown in Figure 5-8 and the individual Qbranches for each value of K are seen to be well resolved. Also shown is a
simulated spectrum at a Boltzmann temperature of 80 K, along with a stick
spectrum calculated using the rotational parameters of Popplewell et al.123 The
K distribution is seen to peak at K = 0 and only states up to K = 3 have
appreciable population. The individual J lines of each QK branch are not resolved
but from the calculated stick spectrum a Jmax value of about 10 is deduced, which
101
indicates that the parent has most of the angular momentum about an axis
perpendicular to the figure axis.
Similar spectra were obtained for CH3I in helium expansions under
conditions corresponding to the near-nascent results of Figure 5-3. Here the
parent was clearly colder, as evidenced by narrower QK branches and by an
increase in the intensity of the K = 0 band relative to the higher K bands. These
spectra shown in Figure 5-8 were simulated too, yielding parent rotational
temperatures of 35 and 50 K at X/D = 8 and 5. Since Q-branches for the
different K values were well separated, the total K populations were more directly
obtained by simply integrating these peaks in the (square-rooted) spectrum. The
results are shown as the hashed bars in Figure 5-9 while the solid bars represent
the K state distributions observed for CH3. Where overlapping occurred for the
CH3 peaks, the population sum was apportioned according to the Boltzmann
predictions. The sum of all of N populations for each K value of CH3 was
obtained and, for both parent and product, the total populations were normalized
to one.
These results show a clear excess population in the higher K states of CH3
compared to CH3I. This trend appears to increase in going from 3 to 6 collisions
so that, under nascent conditions, a closer match of the K distributions would
result. We note that it probably takes two collisions for K to increase in the CH3
product because its high fragmentation velocity component is along the symmetry
102
axis. The first collision is thus much more likely to cause an increase in tumbling
rather than spinning motion.
No parent distributions were accessible in the nascent photofragmentation
studies of Chandler et al.72 but their expansion conditions should have produced
colder CH3I with most of the population in K = 0 and K = 1. (These would have
equal populations at absolute zero, assuming no nuclear spin relaxation). The fact
that they see no product in states higher than K = 3 is reasonably consistent with
the simple picture of "spin" conservation in the dissociation step.
v2 = 1 Rotational Distribution
The relative population of the v2 = 1 rotational states seen in the
near-nascent spectra are tabulated at the bottom of Table 5-6. Comparison with
the population predicted at the Boltzmann temperatures deduced for the v2 = 0
products shows large discrepancies. Efforts to characterize the v2 = 1 distributions
by separate Boltzmann temperatures led to very poor fits and to values of about
800-1.- 350 K for both X/D = 5 and 8 positions. This poor agreement with a
Boltzmann model suggests that the distributions are probably complicated by the
production of v2 = 1 via both I and I* dissociation channels. The I/I* ratio for the
v2 = 1 product has been measured as 0.38 by Chandler et al.72 and as 0.30 by Loo
et al.71 while the same authors obtain ratios of only 0.1 and 0.08 for the v2 = 0
CH3 product. Thus it is perhaps defensible that we have ignored consideration of
103
the I channel product in discussing the v2 = 0 distributions and reasonable that
this neglect leads to poorer fits for the v2 = 1 case. It is also noteworthy that the
hotter rotational distributions that we see for v2 = 1 CH3 are consistent with the
theoretical predictions of Amatatsu et al.117 of greater rotational excitation for the
I versus I* channel (by about 4-5 quanta).
104
Conclusions
The new high resolution CARS setup at Oregon State University was employed
to study the photodissociation dynamics of CH3I at 266 nm. CH3 spectra were
obtained in free jet expansions under near-nascent conditions as well as at higher
densities where many collisions with various molecules occur. The rich spectra
obtained under the latter conditions permitted a slight extension of our earlier
assignments in chapter IV for the individual N, K transitions in the fundamental
region (v2 = 0).
From the analysis of the near-nascent spectra, the v2 = 1 hot
band origin was measured and a number of transitions were assigned and analyzed
to give rotational constants and the x12 anharmonicity constant.
Due to the
complexity in the hot band region, many transitions were left unassigned but a
compilation of these is provided as an aid for possible future work on this radical.
In the near-nascent spectra there was no overlap between the fundamental
and hot band regions and, from integrated areas, the vibrational population ratio
for v2 = 0 : v2 = 1 states was found to be 1.00:0.27(10). This value is in much
better agreement with theoretical calculations than are previous experimental
results.
This ratio indicates that the planar CH3 molecule forms slowly and
adiabatically along the dissociation coordinate, rather than rapidly with excitation
of the bending mode.
The spectra under the near-nascent condition gave rotationally-resolved NK
information for the first time and these data were used to extract rotational
105
population distributions. Fits of these populations to Boltzmann distributions
resulted in rotational temperatures of T = 230(50) K and T = 1180(90) K at X/D
= 8 and 5 jet positions. From rotational populations obtained for both the CH3I
and CH3, the retention of spin angular momentum about the three fold symmetry
axis in the dissociation process was confirmed. Comparisons with distributions
obtained under nascent conditions by Chandler et al.72 show that only small
changes occur in the rotational distributions after 3-6 collisions. An average
rotational energy of about 140 cm-1 is deduced, in good accord with the latest
theoretical estimates.
106
Table 5-1. Relative vibrational and rotational temperatures for CH3
photoproduct
Vibrational Distribution
X(nm)
v2=0
v2=1
v2=2
Method
Ref.
Year
280
1
1.14
1.95
TOF
F.J. Black
1988
266
1
11.8
Theory
1
13.3
TOF
266
(1)
(4)b
14.3
IR-Em
M. Shapiro
R.K. Sparks
H. W. Hermann
1980
266
e
14.7
266
1
0.91
0.91
MPI
R. 0. Loo
1988
266
1
0.26
0.09
1
0.27
Y. Amatatsu
This Work
1991
266
Theory
CARS
248
1
17.2
1
4.67
17
248
1
0.44
0.12
248
1
0.39
0.12
Theory
IR-Abs.
M.D. Barry
G.N.A. van Veen
H. Guo
T. Suzuki
1983
248
TOF
TOF
55.6
1981
1981
1993
1984
1990
1991
Rotational Temperature
Trot(lqc
280
200
TOF
F.J. Black
1988
266
290d
TOF
R.K. Sparks
1981
266
120
MPI
R. 0. Loo
1988
266
120(TN)e
REMPI
D.W. Chandler
1989
CARS
This Work
1993
30(TK)
266
230
a Later unpublished work by this group suggests that these results may be
erroneous (see footnotes in Ref. 8, 15)
b v2 = 0, 1 relative populations of Sparks et al. assumed.
c Temperatures deduced assuming. Boltzmann distribution.
d Calculated from Erot = 300 cm" 1 3/2 kTrot
c Separate Boltzmann temperatures assumed for N, K distributions.
107
Table 5-2. 1)1 Q-branch transition frequencies for v2=0, 1 states of CH3 (cm-1)
N
K
Obs.
Freq.
Rel.a
CARS
Obs.-
Obs.-
Ca lc.
Ca lc.
Int.
No H's
With H's
0
0
3004.445
3
0.019
0.008
1
1
3004.321
4
0.030
0.021
2
2
3004.087
4
0.028
0.017
2
1
3003.972
4
0.022
0.024
2
0
3003.884
14
-0.030
-0.024
3
3
3003.707
21
-0.024
-0.037
3
2
3003.528
7
-0.022
-0.018
3
1
3003.424
6
-0.017
-0.005
4
4
3003.294
12
-0.013
-0.029
4
3
3003.042
23
-0.013
-0.009
4
2
3002.876
8
0.001
0.013
4
1
3002.785
22
0.017b
0.033b
5
5
3002.785
22
-0.004b
-0.0196
4
0
3002.717
46
-0.016
0.001
5
4
3002.459
13
-0.007
-0.004
5
3
3002.230
32
0.013b
0.020
6
6
3002.174
60
-0.0056
-0.015b
5
2
3002.040
15
-0.001
0.010
5
1
3001.930
16
-0.005
0.004
6
5
3001.783
13
-0.003
0.001
7
7
3001.474
41
-0.003b
-0.004b
6
4
3001.474
41
0.005b
0.013b
6
3
3001.231
36
0.007
0.012
6
2
3001.045
50
-0.0066
-0.007b
7
6
3001.021
50
0.005
0.009
108
Table 5-2. Continued
N
K
Obs.
Freq.
Rel.a
CARS
Obs.Cale.
Obs.-
Int.
No H's
With H's
Ca lc.
6
1
3000.924
50
-0.023b
-0.031b
6
0
3000.924
50
0.011
0.001
8
8
3000.695
19
0.010
0.019
7
5
3000.635
28
0.002
0.009
7
4
3000.335
16
0.013
0.015
8
7
3000.185
12
0.025
0.027
7
3
3000.094
42
0.011
0.004
7
2
2999.935
21
0.022
0.003
7
1
2999.813
70
0.001b
-0.02611
9
9
2999.812
70
0.003
0.022
8
6
2999.698
49
-0.012
-0.008
8
5
2999.333
10
-0.003
0.002
9
8
2999.227
20
0.009
-0.003
8
4
2999.040
12
0.007
0.007
10
10
2998.863
59
0.014
0.029b
8
3
2998.812
53
0.012
0.003
9
7
2998.669
10
-0.037
-0.043
8
2
2998.619
12
-0.016
-0.036
8
1
2998.535
52
-0.001
-0.030b
8
0
2998.535
52
0.032
-0.001
10
9
2998.201
100
0.006
-0.041
9
6
2998.201
100
-0.068
-0.057
9
5
2997.869
28
-0.037
-0.011
11
11
2997.788
30
-0.021
-0.036
10
8
2997.703
13
0.081
0.048b
109
Table 5-2. Continued
N
K
Obs.
Freq.
Rel.a
CARS
Obs.Ca lc.
Obs.Cale.
hit.
No H's
With H's
9
4
2997.590
13
-0.022
0.011b
9
3
2997.399
37
0.014
0.046
11
10
2997.251
11
amb
0.033
9
2
2997.179
12
-0.046b
-0.018
10
7
2997.105
21
-0.022b
0007
9
1
2997.105
21
-0.024b
-0.001
12
12
2996.796
60
0.100
0.010
-0.062
10
6
2996.573
79
0131b
11
9
2996.573
79
0.111b
0.014
10
5
2996.285
17
-0.067b
0.050
10
4
2995.886
29
0181b
-0.020
10
3
2995.658
46
-0.190b
-0.017
10
2
2995.508
30
-0.185b
0001b
10
1
2995.433
18
-0.167b
0.023b
10
0
2995.657
18
0.088b
-0.043b
13
12
2995.187
71
0.515b
-0.007
11
6
2994.808
74
-0.216b
0.032
15
15
2993.902
83
0.981b
0.002
18
18
2992.710
44
4.099b
0.000
12
6
2992.584
43
-0.658b
-0.007
13
9
2992.480
66
-0.209b
-0.005
110
Table 5-2. Continuedc
N
K
Obs.
Freq.
Rel.a
CARS
Obs.-
Obs.-
Ca lc.
Cak.
Int.
No H's
1
0
2996.012
19
-0.009
2
1
2995.705
16
0.011
3
3
2995.492
30
0.004
3
0
2995.164
11
0.045
4
1
2994.406
19
-0.085
5
0
2993.672
32
0.008
6
1
2992.904
11
0.039
7
0
2991.933
16
-0.011
8
1
2991.165
22
-0.003
With H's
a Intensities from spectrum shown in Fig. 1.
b Indicates lines not used in linear regression analysis due to overlap or
uncertain assignment.
c The assignments for v2 = 1 state are given in this portion of the table.
111
Table 5-3. Unassigned transition frequencies and their relative CARS intensities
in the overlap region with the hot bandsa
2996.692
17
2996.573
38
23
2983.148
27
2977.585
27
79
2989.437
2989.300
2982.941
10
2977.526
12
2996.285
10
2988.770
23
2982.886
12
2977.297
18
2996.050
19
2988.639
54
2982.810
17
2977.259
21
2995.887
29
2988.537
22
2982.740
9
2977.211
21
2995.750
16
2988.445
11
2982.299
10
2977.147
9
2995.658
46
2988.359
22
2982.146
14
2976.983
9
2995.508
30
2988.057
15
2982.109
14
2976.907
14
2995.433
18
2987.935
16
2982.007
28
2976.834
14
2995.239
71
2987.855
22
2981.933
18
2976.755
9
2995.078
11
2987.580
56
2981.856
27
2976.662
18
2995.014
16
2987.445
12
2981.801
19
2976.469
9
2994.942
11
2987.336
12
2981.703
11
2976.362
10
2994.617
11
2987.205
10
2981.506
20
2976.259
10
2994.503
22
2987.117
22
2981.377
10
2976.186
35
2994.406
19
2987.029
26
2981.297
22
2976.125
13
2994.297
36
2986.864
13
2981.184
22
2976.034
7
2994.188
14
2986.719
13
2981.072
63
2975.970
8
2994.130
20
2986.620
19
2980.998
17
2975.888
7
2993.780
21
2986.186
26
2980.929
17
2975.813
11
2993.674
32
2986.129
12
2980.880
29
2975.644
17
2993.592
14
2986.038
12
2980.800
29
2975.599
17
2993.489
11
2985.910
25
2980.747
11
2975.518
17
2993.096
28
2985.849
31
2980.534
11
2975.457
10
2993.024
14
2985.771
28
2980.330
16
2975.384
8
2992.930
11
2985.713
11
2980.228
26
2975.309
16
2992.896
27
2985.563
13
2980.151
15
2975.240
13
2992.828
27
2985.494
19
2980.035
15
2975.119
14
2992.656
16
2985.415
19
2979.970
13
2975.003
11
2991.967
16
2985.201
18
2979.925
12
2974.934
12
112
Table 5-3. Continued
2991.905
16
2984.946
17
2979.879
12
2974.857
15
2991.765
30
2984.878
12
2979.814
11
2974.616
10
2991.379
53
2984.810
12
2979.432
18
2974.569
9
2991.323
47
2984.703
37
2979.118
10
2974.511
9
2991.245
22
2984.608
15
2979.060
9
2974.392
15
2991.174
22
2984.535
18
2978.912
17
2974.328
14
2991.036
26
2984.386
18
2978.836
20
2974.245
11
2990.970
26
2984.324
13
2978.748
16
2974.181
15
2990.773
11
2984.237
46
2978.694
10
2974.072
10
2990.720
11
2984.101
10
2978.612
16
2973.967
12
2990.556
28
2984.053
14
2978.405
11
2973.919
12
2990.474
44
2984.005
11
2978.311
11
2973.870
10
2990.374
56
2983.934
14
2978.264
11
2973.766
12
2990.296
40
2983.854
14
2978.124
26
2973.701
12
2990.154
19
2983.713
33
2978.054
14
2973.625
11
2990.089
19
2983.643
15
2977.963
9
2973.520
11
2989.976
11
2983.531
13
2977.881
12
2973.467
17
2989.779
58
2983.490
13
2977.798
13
2989.698
58
2983.390
11
2977.703
13
2989.561
12
2983.261
20
2977.626
27
a Frequencies are the average of 2-4 measurements with standard
deviations less than 0.01 cm 1. Intensities are from the spectrum shown in
Fig. 1.
113
Table 5-4. Vibrational-rotational parameters for CH3 (cm-1)
u
CARS
This work
(1000)440000)
3004.426(11)
aI3
0.0856(7)
aC
0.0489(6)
0.0471(6)
0.0536(103
DNO-DNla
-46(9)
-168(20)
-334(45)
DNKO-DNK1
53(20)
331(44)
-244(1300)
-20(12)
-131(26)
(350)b
Trans.
DKO-DK1
CARS
This work
CARS
This work
(1100)440100)
(1000),-(0000)
3004.436(12)
0.0890(10)
2996.21(4)
0.0948(31)
-0.98(12)
HNO-HN1
HNKO-HNK1
2.21(4)
HKNo-HKNI
-0.22(49)
HKO-HK1
-0.82(21)
Level
0000
1000
1000
0100
1100
Ref.
20
This work
This work
20
This work
3004.426
3004.436
606.4531
u
2996.21
B
9.57789
9.49232
9.48891
9.2581
9.16329
C
4.74202
4.69311
4.69490
4.8116
4.75799
770
816
938
494
828
DNK
DK
-1358
-1411
-1689
-706
-462
257
(_93)b
HN
-0.32
0.66
HNK
1.00
-1.21
HKN
-0.40
-0.18
HK
-0.20
0.62
DN
R(A)
634
1.07895
654
1.08380
765
1.08400
1.09743
1.10309
a D and H values should be multiplied by 10-6.
b This value is calculated using the planarity condition 2DN + 3DNK + 4DK =
0.
114
Table 5-5. Calculated rotational temperatures (Boltzmann dist.) and number of
collisions for CH3 in the jet. Experimental conditions as well as collision
diameters used in calculations are also given.
Driving
gas
Collisiona
Dia.(nm)
Number of
Collisions
6
14
Ar
Ne
He
Ethane
0.34
0.28
0.26
0.54
X/D
3
2
Press.
Atm
20
2
20
20
20
620( 90)
660(100)
1090(150)
1140(210)
2
4
20
20
20
20
20
20
760(170)
820( 90)
1010(140)
1140(200)
1010(190)
1230(220)
1
1
1
2
14
2
2
2
1
0.5
0.1
0.3
Trot
Boltz.
2
23
50
24
50
140
240
320
Collision
Time (ns)
4
2
2
1
8
4
20
4
5
4
20
230( 50)
340( 90)
20
3
4
25
840(240)
490
0.3
4
20
1160(160)
6300
0.5
4
370
930(140)
230
330
500
0.3
0.3
0.3
0.3
2.6
4.2
20
20
20
720( 70)
650( 90)
580( 90)
490( 70)
1740
7
4.7
120
a Diameters are from Ref. 40. Values of 0.36 and 0.50 nm were used for
CH3 and I.
115
Table 5-6. Rotational population distribution for near-nascent CH3 along with
calculated Boltzmann values.
v2
N
K
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
2
2
2
1
2
0
3
3
3
3
1
4
4
4
4
2
3
5
2
4
5
3
6
5
6
2
5
1
6
5
6
3
6
2
8
8
7
5
0
7
4
0
8
7
0
7
0
0
7
3
2
7
1
0
8
1
1
6
0
1
2
1
1
3
3
1
3
0
1
4
1
1
5
0
1
6
1
1
7
8
0
1
1
X/D = 5
X/D = 8
-6 Coll.
-3 Coll.
Rel. NNK
0.53
0.42
0.58
0.44
1.00
0.88
0.49
0.66
0.45
0.57
0.23
0.46
0.75
0.28
0.38
0.53
0.49
0.43
0.39
0.28
0.21
0.32
0.40
0.26
0.25
0.45
0.26
0.52
0.40
0.29
0.36
0.30
0.74
0.33
0.37
0.43
Rel. NNK
0.20
0.28
0.42
0.40
0.78
1.03
0.47
0.44
0.55
0.96
0.43
0.45
0.79
0.99
0.35
0.33
0.40
0.57
0.26
0.34
0.26
0.22
0.25
0.38
0.17
0.16
0.39
0.55
0.40
1.03
0.87
0.42
0.68
0.26
0.34
0.10
Rel. NNK
0.47
0.40
0.53
0.40
1.00
0.67
0.32
0.49
0.34
0.48
0.17
0.37
0.44
0.37
0.41
0.41
0.33
0.33
Ref. 72
Nascent
Rel. NNK
0.23
0.31
0.45
0.41
0.80
1.02
0.44
0.40
0.50
0.81
0.35
0.33
0.54
0.70
0.23
0.21
0.25
0.31
0.38
0.45
0.61
0.39
0.28
0.83
0.41
0.34
0.53
0.80
0.33
0.44
0.13
0.13
0.03
0.41
Rel. NNK
0.63
0.65
0.29
0.61
1.00
0.15
0.26
0.43
0.43
0.24
0.03
0.15
116
2970
2975
2980
WAVENUMBERS
Figure 5-1. High resolution CARS spectra of CH3 produced by 266 nm photolysis
at X/D=1 in a jet expansion of 23% CH3I in argon at 2 atm. See text for
discussion of assignments.
117
rot
No. of Collisions
(b) 340
-6
(c) 840
20
A
1
2987
2991
i
I
I
2995
I
2999
3003
WAVENUMBERS
Figure 5-2. CH3 CARS spectra produced by photolysis of 0.46 atm CH3I in a He
jet at various driving pressures. For experimental conditions of each spectrum see
Table 5.
118
2989
2991
2993
2995
2997
2999
3001
3003
3005
WAVENUMBERS
Figure 5-3. High resolution CARS spectra of CH3 obtained under near-nascent
condition. The simulated spectra are also shown for each spectrum.
119
00
-2.6
_
Trot = -1/SLOPE
oll
= 230 (40) K
22
0
0 20
1
0 330
NK
031
32
520 051
0 44
0 54
0 43
0 65
0 42
053
-5.0
0 66
0 63
0
200
400
600
E(NK)/1( (K)
Figure 5-4. Boltzmann fit of CH3 CARS spectrum of Figure 5-3 (top spectrum).
The NK quantum numbers are shown to the right of each data point.
120
0
1
2
3
4
Log(No. of Collisions)
Figure 5-5. CH3 rotational temperatures (assuming Boltzmann distribution) as a
function of log of total number of collisions for several carrier gases. See Table 5
for experimental conditions.
121
0.18
41
55
Exp.
- 3 Collisions
Calc.
(230 K)
0.14
0.10
61
76
77
0.06
0.02
0.14
41
55
gm. Exp.
- 6 Collisions
Calc.
(340 K)
0.10
0.06
0.02
0020406080
1121315171
223242526272
3343536373 44546474
6575
6686
87
88
NK
Figure 5-6. Relative CH3 rotational populations for individual NK states in the
fundamental region (v2 = 0) for the two near nascent spectra shown in Figure 5-3.
NK values are shown below for different K groups. Contributions from other
overlapping transitions are included and are labelled above.
122
1.0
Nascent
- 3 Collisions
- 6 Collisions
0.8 -
0.2
0.0
00 20
11
21
31
22
51
32 42 52
33
43
NK
Figure 5-7. Comparison between the CH3 NK nascent distributions of
Chandler et al.72 and the near-nascent distributions for the two cases shown
in Figure 5-3. Only non-overlapping transitions are included.
123
QK
I
2
3
1
01
(a)
Caic., Trot
35 K
(b)
X/D = 5
(c)
Cak., Trot - 50 K
(d)
(e)
I
2970.5
2970.7
I
I
2970.9
2971.1
WAVENUMBERS
i
2971.3
2971.5
Figure 5-8. High resolution CARS Q-branch jet spectrum of CH3I in the u1 C-H
symmetric stretching region. a) Obs. spectrum at X/D=8. b) Calculated spectrum
assuming Boltzmann distribution at 35 K. c) Obs. spectrum at X/D=5. d)
Calculated spectrum assuming Boltzmann distribution at 50 K. e) Stick spectrum
for 50 K distribution.
124
CH3 I
- 3 Collisions
0.40
CH3
0.30
0.20
0.10
0.40
- 6 Collisions
0.30
0.20
0.10
0.00
0
1
2
3
4
5
6
7
8
K
Figure 5-9. Relative CH3 rotational populations for individual K states in the
fundamental region (v2 = 0) for the two near-nascent spectra shown in Figure 5-3.
125
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H. Murphy and D. Miller, J. Phys. Chem. 88, 4474 (1984).
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R. E. Palmer, "CARSFT Computer Code", Sandia Report SAND898206, UC-13, NTIS copy A03.
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I. N. Levine, Molecular Spectroscopy, p. 224, Wiley, New York (1975).
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T. Shimanouchi, Tables of Molecular Vibrational Frequencies, Vol.
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(1993).
107.
B. Scharadar and W. Meier, Raman and Infrared Atlas of Organic
Compounds, page A2-44.
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Mansour Zahedi, Ph.D. thesis, Oregon State University, 1993.
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APPENDICES
133
Appendix A
Quick Basic 4.5 source codes written for Tektronix digital oscilloscope
model 2440
134
9**********************************************************************
'PROGRAM WRI1 TEN FOR TEKTRONIX DIGITAL OSCILLOSCOPE-2440
'TO TRANSFER WAVEFORMS FROM THE SCOPE TO THE IBM-PC
'CALLED "TEKWTRAN6.BAS"
'MANSOUR ZAHEDI AUG.29.1990 ; VERSION MODIFIED JUNE.7.1991
,**********************************************************************
CLS : KEY OFF: LOCATE 25, 1: PRINT "Press any key to exit program";: LOCATE 1, 1
'***** Establish communication with device driver *****
OPEN "$DV488" FOR OUTPUT AS #1
PRINT #1, "BUFFERCLEAR"
OPEN "$DV488" FOR INPUT AS #2
ON ERROR GOTO ERSVC
'***** Initialize MBC-488 board using "SYSCON" command *****
PRINT #1, "SYSCON MAD1=3 CIC1=1 BA1=&H200 CLK=8"
'***** Read Serial Poll byte *****
CLS
COLOR 0, 7
LOCATE 3, 35
PRINT " WARNINGS !!!! "
COLOR 7, 0
PRINT : PRINT "YOU MUST HAVE THE TWO SYSTEM FILES CALLED VIPARSE.SYS
"
PRINT "AND DV488PC.SYS IN C: \UTIL SUBDIRECTORY, ALSO ADD THE"
PRINT "LINES BELOW TO THE END OF YOUR CONFIG.SYS FILE, GOOD LUCK!"
PRINT "device= C: \UTIL \VIPARSE.SYS /HK=ALT H /MK=ALT M /SK=ALT TAB"
PRINT "device=CAUTIL\DV488PC.SYS"
PRINT : PRINT "HIT ANY KEY TO CONTINUE!"
WHILE INKEY$ = "": WEND
CLS : PRINT #1, "STATUS 12"
INPUT #2, SPOLL%
PRINT : PRINT " Testing Serial Poll Byte for 'RSV'"
PRINT : PRINT " Serial Poll Byte = &H"; HEX$(SPOLL%): PRINT
IF (SPOLL% AND 8) <> 8 THEN PRINT " No Request In Serial Poll Byte"
ELSE GOTO EVENT
'***** Set TIMEOUT (timeout time=0.056 x A%) *****
TIMEOUT:
A% = 100
PRINT #1, "TIMEOUT", A%
'***** WAVEFORM TRANSFER ROUTINE FOR TEK-2440 ***"
DIM WAVE%(5000)
135
DIM SIG!(5000)
DIM RESP$(50)
DIM EVENTS(50)
DIM ANSWRS(100)
GOTO GETCHANNEL
GETCHANNEL:
PRINT : PRINT " Choose A Channel For Your Data Source! (1 OR 2)?"
REP$ = INPUT$(1)
PRINT #1, "OUTPUT 12 $ +", "PATH OFF"
IF REPS = "1" THEN COMM1$ = "DATA SOURCE:CH1": CLS : PRINT : PRINT " * * * * * Data
Source Is Channel 1 *****": GOTO GETNUM
IF REPS = "2" THEN COMM1$ = "DATA SOURCE:CH2": CLS : PRINT : PRINT " ***** Data
Source Is Channel 2 *****": ELSE CLS : GOTO GETCHANNEL
GETNUM:
PRINT : INPUT " Enter Number Of Data Points To Be Transferred (Max. # = 1023)";
NUMDATA%
IF NUMDATA% = 0 THEN NUMDATA% = 1000
IF NUMDATA% > 1023 THEN NUMDATA% = 1023
CLS : PRINT : PRINT " ***** Number Of Data Points = "; NUMDATA%; ""*""
ACQMODE:
PRINT : PRINT " Choose Data Acquisition Mode! : Normal, Average, Envelope (N, A, E),
[Def=N]"
DA$ = INPUT$(1)
IF DA$ = "N" OR DA$ = "n" OR DA$ = "A" OR DAS = "a" OR DA$ = "E" OR DA$ = "e"
THEN
GOTO CONT
ELSE CLS : DAS = "N": GOTO CONT
END IF
CONT:
SELECT CASE DA$
CASE "N", "n"
CLS : PRINT : PRINT " ***** Data Acquisition Mode Is Normal *****"
COMM3$ = "ACQUIRE MODE:NORMAL"
PRINT #1, "OUTPUT 12 $ +", COMM3$
GOTO GETRESP
CASE "A", "a"
CLS : PRINT : PRINT " ***** Data Acquisition Mode Is Average *****"
COMM6$ = "ACQUIRE MODE:AVG"
PRINT : PRINT " Choose Number Of Waveforms To Be Averaged (2 ^ n); (n=1,2,...,8) ?"
NM = INPUT$(1)
IF NM = "1" THEN NA% = 2: COMM4$ = "ACQUIRE NUMAVG:2": GOTO GETRESP
IF NM = "2" THEN NA% = 4: COMM4$ = "ACQUIRE NUMAVG:4": GOTO GETRESP
IF NA$ = "3" THEN NA% = 8: COMM4$ = "ACQUIRE NUMAVG:8": GOTO GETRESP
IF NM = "4" THEN NA% = 16: COMM4$ = "ACQUIRE NUMAVG:16": GOTO GETRESP
IF NM = "5" THEN NA% = 32: COMM4$ = "ACQUIRE NUMAVG:32": GOTO GETRESP
136
IF NM = "6" THEN NA% = 64: COMM4$ = "ACQUIRE NUMAVG:64": GOTO GETRESP
IF NM = "7" THEN NA% = 128: COMM4$ = "ACQUIRE NUMAVG:128": GOTO GETRESP
IF NM = "8" THEN NA% = 256: COMM4$ = "ACQUIRE NUMAVG:256": GOTO GETRESP
CASE "E", "e"
CLS : PRINT : PRINT " ***** Data Acquisition Mode Is Envelope *****"
COMM3$ = "ACQUIRE MODE:ENV"
PRINT : PRINT " Choose Number Of Waveforms To Be Enveloped (2 ^ n), (n=1,2,...,8); Or"
PRINT " Choose Continuous Mode (C)"
NES = INPUT$(1)
IF NE$ = "1" THEN NE% = 2: COMMS$ = "ACQUIRE NUMENV:2": GOTO GETRESP
IF NE$ = "2" THEN NE% = 4: COMMS$ = "ACQUIRE NUMENV:4": GOTO GETRESP
IF NE$ = "3" THEN NE% = 8: COMM5$ = "ACQUIRE NUMENV:8": GOTO GETRESP
IF NE$ = "4" THEN NE% = 16: COMMS$ = "ACQUIRE NUMENV:16": GOTO GETRESP
IF NE$ = "5" THEN NE% = 32: COMM5$ = "ACQUIRE NUMENV:32": GOTO GETRESP
IF NE$ = "6" THEN NE% = 64: COMM5$ = "ACQUIRE NUMENV:64": GOTO GETRESP
IF NE$ = "7" THEN NE% = 128: COMMS$ = "ACQUIRE NUMENV:128": GOTO GETRESP
IF NE$ = "8" THEN NE% = 256: COMMS$ = "ACQUIRE NUMENV:256": GOTO GETRESP
IF NE$ = "C" OR NE$ = "c" THEN COMM5$ = "ACQUIRE NUMENV:CONT"
END SELECT
GETRESP: CLS
PRINT : PRINT " Do You Want To Smooth The Waveform? (Y OR N), [Def=N]"
RESP$ = INPUT$(1)
IF RESP$ = "Y" OR RESP$ = "y" THEN
COMM$ = "SMOOTH ON"
CLS : PRINT : PRINT " ***** The Waveform Is Smoothed *****"
PRINT #1, "OUTPUT 12 $ +", COMM$
GOTO GETREPP
END IF
NONE: IF RESP$ = "N" OR RESP$ = "n" THEN
COMM$ = "SMOOTH OFF"
PRINT #1, "OUTPUT 12 $ +", COMM$
CLS
GOTO GETREPP
END IF
RESP$ = "N": GOTO NONE
GETREPP:
PRINT : PRINT " Do You Want Volt Conversion Of Your Data? (Y Or N)"
PRINT " If So, Choose Rlbinary (Signed Integer) Or RPbinary (Positive Integer) Next."
REPP$ = INPUT$(1)
IF REPP$ = "Y" OR REPP$ = "y" OR REPP$ = "N" OR REPP$ = "n" THEN GOTO HERE
ELSE CLS : GOTO GETREPP
HERE: CLS
PRINT : PRINT " Choose Data Format You Want? RIbinary, RPbinary, AScii or QUit (RI, RP,
AS, QU)"
PRINT : PRINT " [Default = RI]"
DF$ = INPUT$(2)
IF DF$ = "AS" OR DF$ = "as" OR DF$ = "RP" OR DF$ = "rp" OR DF$ = "RI" OR DF$ =
137
"ri" OR DF$ = "QU" OR DF$ = "qu" THEN
GOTO CONTIN
ELSE CLS : DES = "RI": GOTO CONTIN
END IF
CONTIN:
SELECT CASE DF$
CASE "AS", "as"
CLS : PRINT : PRINT " ***** The Data Format Is Ascii
COMMO$ = "DATA ENCDG:ASCII"
GOTO GETPK2PK
CASE "RP", "rp"
CLS : PRINT : PRINT " ***** The Data Format Is Positive Integer *****"
COMMO$ = "DATA ENCDG:RPBINARY"
GOTO GETPK2PK
CASE "RI", "ri"
CLS : PRINT : PRINT " ***** The Data Format Is Singed Integer *****"
COMMOS = "DATA ENCDG:RIBINARY"
GOTO GETPK2PK
CASE "QU", "qu"
END
END SELECT
'***** PEAK TO PEAK MEASUREMENT SET UP *****
GETPK2PK:
ONEPOSORIG! = 0
TWOPOSORIG! = 0
PRINT #1, "OUTPUT 12 $ +", "CURSOR? 'ITOS:ONE"
PRINT #1, "ENTER 12 $ +", ONEPOSORIG!
INPUT #2, ONEPOSORIG!
PRINT #1, "OUTPUT 12 $ +", "CURSOR? TPOS:TWO"
PRINT #1, "ENTER 12 $ +", TWOPOSORIG!
INPUT #2, TWOPOSORIG!
CLS : PRINT : PRINT " Would You Like A Peak To Peak Measurement Of The Waveform (Y
Or N)?"
PP$ = INPUTS(1)
FE$ = ""
SELECT CASE PP$
CASE "Y", "y"
IF DA$ = "A" OR DA$ = "a" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF ELSE GOTO ENVEL2
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
138
Keyboard (M Or K)?"
PRINT " [Default = M]"
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUALO
ELSE OW$ = "M"
END IF
USUALO:
IF REP$ = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR: GOTO AVGPK2PK
ENVEL2:
IF DA$
= "E" OR DA$ = "e" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF' ELSE GOTO NORM2
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = M]"
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL01
ELSE OW$ = "M"
END IF
USUAL01:
IF REPS = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REPS = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR: GOTO ENVPK2PK
NORM2:
IF DA$ = "N" OR DA$ = "n" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFFPRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = M]"
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL02
ELSE OW$ = "M"
END IF
USUAL02:
IF REP$ = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR
GOSUB PK2PK
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETAREA
EVEFLAG% = 0
139
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO USUAL02
GOTO GETPK2PK
CASE "N", "n"
IF DA$ = "A" OR DA$ = "a" THEN
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF': GOTO GETAREA
ELSE GOTO ENVELOPE2
END IF
ENVELOPE2:
IF DA$ = "E" OR DA$ = "e" THEN
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF': GOTO GETAREA
ELSE GOTO NORMAL2
END IF
NORMAL2:
IF DA$ = "N" OR DA$ = "n" THEN PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF':
GOTO GETAREA
CASE ELSE
GOTO GETPK2PK
END SELECT
ENVPK2PK:
IF NE$ =
IF NE$ =
IF NE$ =
IF NES =
IF NE$ =
IF NE$ =
IF NES =
IF NE$ =
"1" THEN NE%
"2" THEN NE%
"3" THEN NE%
"4" THEN NE%
"5" THEN NE%
"6" THEN NE%
"7" THEN NE%
"8" THEN NE%
READPK2PK1:
=
=
=
=
=
=
=
=
2: GOTO READPK2PK1
4: GOTO READPK2PK1
8: GOTO READPK2PK1
16: GOTO READPK2PK1
32: GOTO READPK2PK1
64: GOTO READPK2PK1
128: GOTO READPK2PK1
256: GOTO READPK2PK1
FOR I% = 1 TO NE%
REPET: GOSUB PK2PK
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETVAlUE2
EVEFLAG% = 0
I% = I% - 1
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO READPK2PK1
GETVAIUE2:
140
OLDPK2PK! = VAL(RESPOND$)
NEWPK2PK! = NEWPK2PK! + OLDPK2PK!
NEXT I%
ENVPK2PK! = NEWPK2PK! / NE%
CLS : PRINT : PRINT " * * * * * The Waveform Averaged Peak To Peak Voltage Is
ENVAREA!; " V"; " *****"
GOTO GETAREA
AVGPK2PK:
IF NAS = "1" THEN NA%
IF NM = "2" THEN NA%
IF NM = "3" THEN NA%
IF NM = "4" THEN NA%
IF NM = "5" THEN NA%
IF NM = "6" THEN NA%
IF NM = "7" THEN NA%
IF NM = "8" THEN NA%
=
=
=
=
=
=
=
=
2: GOTO READPK2PK
4: GOTO READPK2PK
8: GOTO READPK2PK
16: GOTO READPK2PK
32: GOTO READPK2PK
64: GOTO READPK2PK
128: GOTO READPK2PK
256: GOTO READPK2PK
READPK2PK:
FOR I% = 1 TO NA%
REP2: GOSUB PK2PK
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETVA12
EVEFLAG% = 0
I% = I% - 1
DO UNTIL INKEY$ = "R" OR IN10EY$ = "r"
LOOP
GOSUB CURSOR
GOTO READPK2PK
GETVA12:
OLDPK2PK! = VAL(RESPOND$)
NEWPK2PK! = NEWPK2PK! + OLDPK2PK!
NEXT I%
AVGPK2PK! = NEWPK2PK! / NA%
CLS : PRINT : PRINT " ***** The Waveform Averaged Peak To Peak Voltage Is = ";
AVGPK2PK!; " V"; " *****"
'***** AREA MEASUREMENT SET UP *****
GETAREA:
ONEPOSORIG! = 0
TWOPOSORIG! = 0
PRINT #1, "OUTPUT 12 $ +", "CURSOR? TPOS:ONE"
PRINT #1, "ENTER 12 $ +", ONEPOSORIG!
INPUT #2, ONEPOSORIG!
PRINT #1, "OUTPUT 12 $ +", "CURSOR? TPOS:TWO"
PRINT #1, "ENTER 12 $ +", TWOPOSORIG!
INPUT #2, TWOPOSORIG!
PRINT : PRINT " Would You Like An Area Measurement Of The Waveform (Y Or N)?"
141
AM$ = INPUT$(1)
FE$ = ""
SELECT CASE AM$
CASE "Y", "y"
IF DA$ = "A" OR DA$ = "a" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF' ELSE GOTO ENVEL1
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = M]"
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL
ELSE OW$ = "M"
END IF
USUAL:
IF REPS = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR: GOTO AVGAREA
ENVELl:
IF DA$ = "E" OR DA$ = "e" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF' ELSE GOTO NORM1
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = Mr
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL1
ELSE OW$ = "M"
END IF
USUALl:
IF REP$ = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR: GOTO ENVAREA
NORM1:
IF DA$ = "N" OR DA$ = "n" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF'
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = Mr
142
OW$ = 1NPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL2
ELSE OW$ = "M"
END IF
USUAL2:
IF REP$ = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR
GOSUB AREA
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETRISE
EVEFLAG% = 0
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO USUAL2
GOTO GETAREA
CASE "N", "n"
IF DA$ = "A" OR DA$ = "a" THEN
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF': GOTO GETRISE
ELSE GOTO ENVELOPE1
END IF
ENVELOPE1:
IF DAS = "E" OR DA$ = "e" THEN
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF': GOTO GETRISE
ELSE GOTO NORMAL1
END IF
NORMALl:
IF DA$ = "N" OR DA$ = "n" THEN PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF":
GOTO GETRISE
CASE ELSE
GOTO GETAREA
END SELECT
ENVAREA:
IF NES
IF NE$
IF NE$
IF NE$
IF NE$
IF NE$
= "1" THEN NE% =
= "2" THEN NE% =
= "3" THEN NE% =
= "4" THEN NE% =
= "5" THEN NE% =
= "6" THEN NE% =
2: GOTO READRISE2
4: GOTO READRISE2
8: GOTO READRISE2
16: GOTO READRISE2
32: GOTO READRISE2
64: GOTO READRISE2
143
IF NE$ = "7" THEN NE% = 128: GOTO READRISE2
IF NE$ = "8" THEN NE% = 256: GOTO READRISE2
READRISE2:
FOR I% = 1 TO NE%
REPEAT: GOSUB AREA
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETVAIUE1
EVEFLAG% = 0
I% = I% - 1
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO READRISE2
GETVAIUE1:
OLDAREA! = VAL(RESPOND$)
NEWAREA! = NEWAREA! + OLDAREA!
NEXT I%
ENVAREA! = NEWAREA! / NE%
CLS : PRINT : PRINT " ***** The Waveform Averaged Area Is = "; ENVAREA!; " s"; " *****"
GOTO GETRISE
AVGAREA:
NA% = 2: GOTO READAREA
NA% = 4: GOTO READAREA
NA% = 8: GOTO READAREA
NA% = 16: GOTO READAREA
NA% = 32: GOTO READAREA
IF NAS = "6" THEN NA% = 64: GOTO READAREA
IF NM = "7" THEN NA% = 128: GOTO READAREA
IF NM = "8" THEN NA% = 256: GOTO READAREA
READAREA:
IF NM = "1" THEN
IF NM = "2" THEN
IF NM = "3" THEN
IF NM = "4" THEN
IF NM = "5" THEN
FOR I% = 1 TO NA%
REP1: GOSUB AREA
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETVAll
EVEFLAG% = 0
I% = I% - 1
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO READAREA
GETVAll:
OLDAREA! = VAL(RESPOND$)
NEWAREA! = NEWAREA! + OLDAREA!
NEXT I%
AVGAREA! = NEWAREA! / NA%
144
CLS : PRINT : PRINT " ***** The Waveform Averaged Area Is = "; AVGAREAl; " Vs"; " *****"
'***** RISE TIME MEASUREMENT SET UP *****
GETRISE:
ONEPOSORIG! = 0
TWOPOSORIG! = 0
PRINT #1, "OUTPUT 12 $ +", "CURSOR? TPOS:ONE"
PRINT #1, "ENTER 12 $ +", ONEPOSORIG!
INPUT #2, ONEPOSORIG!
PRINT #1, "OUTPUT 12 $ +", "CURSOR? TPOS:TWO"
PRINT #1, "ENTER 12 $ +", TWOPOSORIG!
INPUT #2, TWOPOSORIG!
PRINT : PRINT " Would You Like A Rise Time Measurement Of The Waveform (Y Or N)?"
RT$ = INPUT$(1)
FE$ = ""
SELECT CASE RT$
CASE "Y", "y"
IF DA$ = "A" OR DA$ = "a" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF' ELSE GOTO ENVEL
PRINT #1, "OUTPUT 12 $
COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = M]"
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL3
ELSE OW$ = "M"
END IF
USUAL3:
IF REP$ = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REPS = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR: GOTO AVGRISE
ENVEL:
IF DA$ = "E" OR DA$ = "e" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF' ELSE GOTO NORM
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default =
OW$ = INPUT$(1)
IF OW$ = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL4
ELSE OW$ = "M"
145
END IF
USUAL4:
IF REP$ = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR: GOTO ENVRISE
NORM:
IF DA$ = "N" OR DA$ = "n" THEN COMM7$ = "CURSOR
FUNCTION:TIME;MEASUREMENT WINDOW:ON;MEAS METHOD:HIST;CURS
UNITS:TIME:BASE;PATH OFF
PRINT #1, "OUTPUT 12 $ +", COMM7$
CLS : PRINT : PRINT " Do You Want To Open The Measurement Window Manually Or Using
Keyboard (M Or K)?"
PRINT " [Default = M]"
OW$ = INPUT$(1)
IF OM = "M" OR OW$ = "m" OR OW$ = "K" OR OW$ = "k" THEN
GOTO USUAL5
ELSE OW$ = "M"
END IF
USUAL5:
IF REPS = "1" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH1"
IF REP$ = "2" THEN PRINT #1, "OUTPUT 12 $ +", "CURS TARG:CH2"
GOSUB CURSOR
GOSUB RISETIME
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO TRANSFER
EVEFLAG% = 0
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO USUAL5
GOTO TRANSFER
CASE "N", "n"
REPEAT3:
IF DA$ = "A" OR DAS = "a" THEN PRINT #1, "OUTPUT 12 $ +", COMM6$ ELSE GOTO
ENVELOPE
PRINT #1, "OUTPUT 12 $ +", COMM4$
DO
NUMACQ$ = ""
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE? NUMACQ"
PRINT #1, "ENTER 12 $ + ", NUMACQ$
LINE INPUT #2, NUMACQ$
IF VAL(NUMACQ$) > NA% THEN
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE MODE:NORM"
PRINT #1, "OUTPUT 12 $ +", "RUN ACQUIRE"
GOTO REPEAT3
END IF
146
LOOP UNTIL VAL(NUMACQ$) = NA%
PRINT #1, "OUTPUT 12 $ +", "RUN SAVE;START 1;STOP 1024;LEVEL 0"
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF'
GOTO TRANSFER
ENVELOPE:
IF DA$ = "E" OR DA$ = "e" THEN PRINT #1, "OUTPUT 12 $ +", COMM3$ ELSE GOTO
NORMAL
PRINT #1, "OUTPUT 12 $ +", COMM5$
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF'
DO
NUMACQ$ = ""
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE? NUMACQ"
PRINT #1, "ENTER 12 $ +", NUMACQ$
LINE INPUT #2, NUMACQ$
LOOP UNTIL VAL(NUMACQ$) = NE%
PRINT #1, "OUTPUT 12 $ +", "RUN SAVE;START 1;STOP 1024;LEVEL 0"
GOTO TRANSFER
NORMAL:
IF DA$ = "N" OR DA$ = "n" THEN PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF":
GOTO TRANSFER
CASE ELSE
GOTO GETRISE
END SELECT
ENVRISE:
IF NES = "1" THEN NE%
IF NE$ = "2" THEN NE%
IF NE$ = "3" THEN NE%
IF NE$ = "4" THEN NE%
IF NE$ = "5" THEN NE%
IF NE$ = "6" THEN NE%
IF NE$ = "7" THEN NE%
IF NE$ = "8" THEN NE%
READRISE1:
=
=
=
=
=
=
=
=
2: GOTO READRISE1
4: GOTO READRISE1
8: GOTO READRISE1
16: GOTO READRISE1
32: GOTO READRISE1
64: GOTO READRISE1
128: GOTO READRISE1
256: GOTO READRISE1
FOR I% = 1 TO NE%
REPEA: GOSUB RISETIME
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETVAIUE
EVEFLAG% = 0
I% = I% - 1
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO READRISE1
GETVAlUE:
147
OLDRTIME! = VAL(RESPOND$)
NEWRTIME! = NEWRTIME! + OLDRTIME!
NEXT I%
ENVRTIME! = NEWRTIME! / NE%
CLS : PRINT : PRINT " ***** The Waveform Averaged Rise Time Is = "; ENVRTIME; " s"; "
*****.
REPEAT2:
PRINT #1, "OUTPUT 12 $ +", COMM3$
PRINT #1, "OUTPUT 12 $ +", COMM5$
DO
NUMACQ$ = ""
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE? NUMACQ"
PRINT #1, "ENTER 12 $ +", NUMACQ$
LINE INPUT #2, NUMACQ$
IF VAL(NUMACQS) > NE% THEN
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE MODE:NORM"
PRINT #1, "OUTPUT 12 $ +", "RUN ACQUIRE"
GOTO REPEAT2
END IF
LOOP UNTIL VAL(NUMACQ$) = NE%
PRINT #1, "OUTPUT 12 $ +", "RUN SAVE;START 1;STOP 1024;LEVEL 0"
GOTO TRANSFER
AVGRISE:
IF NM = "1" THEN NA% =
IF NM = "2" THEN NA% =
IF NM = "3" THEN NA% =
IF NM = "4" THEN NA% =
IF NM = "5" THEN NA% =
IF NM = "6" THEN NA% =
IF NM = "7" THEN NA% =
IF NM = "8" THEN NA% =
2: GOTO READRISE
4: GOTO READRISE
8: GOTO READRISE
16: GOTO READRISE
32: GOTO READRISE
64: GOTO READRISE
128: GOTO READRISE
256: GOTO READRISE
READRISE:
FOR I% = 1 TO NA%
REP: GOSUB RISETIME
IF EVEFLAG% = 1 THEN PRINT : PRINT " Hit <R> To Fix The Cursors Position" ELSE
GOTO GETVAI
I% = I% - 1
EVEFLAG% = 0
DO UNTIL INKEY$ = "R" OR INKEY$ = "r"
LOOP
GOSUB CURSOR
GOTO READRISE
GETVAI:
OLDRTIME! = VAL(RESPONDS)
NEWRTIME! = NEWRTIME! + OLDRTIME!
NEXT I%
AVGRTIME! = NEWRTIME! / NA%
148
CLS : PRINT : PRINT " ***** The Waveform Averaged Rise Time Is = "; AVGRTIME!; " s";
REPEAT1:
PRINT #1, "OUTPUT 12 $
COMM6$
PRINT #1, "OUTPUT 12 $ +", COMM4$
DO
NUMACQ$ = ""
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE? NUMACQ"
PRINT #1, "ENTER 12 $ +", NUMACQ$
LINE INPUT #2, NUMACQ$
IF VAL(NUMACQ$) > NA% THEN
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE MODE:NORM"
PRINT #1, "OUTPUT 12 $ +", "RUN ACQUIRE"
GOTO REPEAT1
END IF
LOOP UNTIL VAL(NUMACQ$) = NA%
PRINT #1, "OUTPUT 12 $ +", "RUN SAVE;START 1;STOP 1024;LEVEL 0"
GOTO TRANSFER
Set TIMEOUT (timeout time=0.056 x A%) *****
TIMEOUT2:
A% = 1000
PRINT #1, "TIMEOUT', A%
'***** TEK-2440 DATA TRANSFER ROUTINE *****
TRANSFER:
PRINT : PRINT " Data Transfer In Progress!"
N% = 1
PRINT #1, " OUTPUT 12 $ +", COMMO$
PRINT #1, "OUTPUT 12 $ +", "PATH OFF'
PRINT #1, "OUTPUT 12 $ +", COMMIS
PRINT #1, "OUTPUT 12 $ +", "CH1? VOLTS"
PRINT #1, "ENTER 12 $ +", CH1V$
LINE INPUT #2, CH1V$
PRINT #1, "OUTPUT 12 $ +", "CH2? VOLTS"
PRINT #1, "ENTER 12 $ 4-", CH2V$
LINE INPUT #2, CH2V$
PRINT #1, "OUTPUT 12 $ +", "HORIZONTAL? ASECDIV"
PRINT #1, "ENTER 12 $ +", SWEEPTIME$
LINE INPUT #2, SWEEPTIME$
COMM$ = ""
COMM2$ = "CURVE?"
PRINT : PRINT
PRINT #1, "OUTPUT 12 $ + ", COMM2$
PRINT #1, "ENTER 12 B +", VARSEG(WAVE%(0)), VARPTR(WAVE%(0)), NUMDATA%
PRINT #1, "OUTPUT 12 $ +", "ACQUIRE MODE:NORMAL"
149
PRINT #1, "OUTPUT 12 $ +", "RUN ACQUIRE"
PRINT #1, "OUTPUT 12 $ +", "SMOOTH OFF'
PRINT #1, "OUTPUT 12 $ +", "LOCK OFF'
YOFF$ = ""
YMULT$ = ""
PRINT #1, "OUTPUT 12 $ +", "WFMPRE? YOFF'
PRINT #1, "ENTER 12 $ +", YOFF$
INPUT #2, YOFF$
PRINT #1, " OUTPUT 12 $ +", "WFMPRE? YMULT'
PRINT #1, "ENTER 12 $ +", YMULT$
INPUT #2, YMULT$
MAXVAL! = LBYTE!
MINVAL! = LBYTE!
IF REPP$ = "Y" OR REPP$ = "y" THEN
IF DF$ = "RI" OR DF$ = "ri" THEN GOTO VOLTCONVRI
END IF
IF REPP$ = "Y" OR REPP$ = "y" THEN
IF DF$ = "RP" OR DF$ = "rp" THEN GOTO VOLTCONVRP
END IF
'***** ROW WAVEFORM DATA TRANSFER *****
I% = 1
FOR N% = 1 TO (NUMDATA% / 2)
IF N% = 1 THEN
HBYTE% = WAVE%(N%) / 256
LBYTE% = WAVE%(N%) - (HBYTE%) * 256
SIG!(I%) = HBYTE%
GOTO INCREMENT
END IF
HBYTE% = WAVE%(N%) / 256
LBYTE% = WAVE%(N%) - (HBYTE%) * 256
SIG!(I%) = LBYTE%
I% = I% + 1
SIG!(I%) = HBYTE%
INCREMENT: I% = I% + 1
NEXT N%
BEEP
PRINT " Hit Any Key To Proceed"
CLOSE
END
'***** VOLT CONVERTED SIGNED INTEGER FORMAT DATA TRANSFER *****
VOLTCONVRI:
I% = 1
FOR N% = 1 TO (NUMDATA% / 2)
IF N% = 1 THEN
HBYTE% = WAVE%(N%) / 256
LBYTE% = WAVE%(N%) - (HBYTE%) * 256
150
HBYTE! = (HBYTE% - VAL(YOFF$)) * VAL(YMULT$)
LBYTE! = (LBYTE% - VAL(YOFF$)) * VAL(YMULT$)
SIG!(I%) = HBYTE!
IF LBYTE! > MAXVAL! THEN MAXVAL! = LBYTE!
IF HBYTE! > MAXVAL! THEN MAXVAL! = HBYTE!
IF LBYTE! < MINVAL! THEN MINVAL! = LBYTE!
IF HBYTE! < MINVAL! THEN MINVAL! = HBYTE!
GOTO INCREM1
END IF
HBYTE% = WAVE%(N%) / 256
LBYTE% = WAVE%(N%) - (HBYTE%) * 256
HBYTE! = (HBYTE% - VAL(YOFF$)) * VAL(YMULT$)
LBYTE! = (LBYTE% - VAL(YOFF$)) * VAL(YMULT$)
SIG!(I%) = LBYTE!
I% = I% + 1
SIG!(I%) = HBYTE!
IF LBYTE! > MAXVAL! THEN MAXVAL! = LBYTE!
IF HBYTE! > MAXVAL! THEN MAXVAL! = HBYTE!
IF LBYTE! < MINVAL! THEN MINVAL! = LBYTE!
IF HBYTE! < MINVAL! THEN MINVAL! = HBYTE!
INCREM1: I% = I% + 1
NEXT N%
BEEP
PRINT " Hit Any Key To Proceed"
CLOSE
WHILE INKEY$ = "": WEND
GOSUB PLOT
END
VOLT CONVERTED POSITIVE INTEGER FORMAT DATA TRANSFER *****
VOLTCONVRP:
I% = 1
FOR N% = 1 TO (NUMDATA% / 2)
IF N% = 1 THEN
HBYTE% = WAVE%(N%) / 256
LBYTE% = WAVE%(N%) - (HBYTE%) * 256
HBYTE! = (HBYTE% - 127 - VAL(YOFF$)) * VAL(YMULT$)
LBYTE! = (LBYTE% - 127 - VAL(YOFF$)) * VAL(YMULT$)
SIG!(I%) = HBYTE!
IF LBYTE! > MAXVAL! THEN MAXVAL! = LBYTE!
IF HBYTE! > MAXVAL! THEN MAXVAL! = HBYTE!
IF LBYTE! < MINVAL! THEN MINVAL! = LBYTE!
IF HBYTE! < MINVAL! THEN MINVAL! = HBYTE!
GOTO INCREM2
END IF
151
HBYTE% = WAVE%(N%) / 256
LBYTE% = WAVE%(N%) - (HBYTE%) * 256
HBYTE! = (HBYTE% - 127 - VAL(YOFFS)) * VAL(YMULTS)
LBYTE! = (LBYTE% - 127 - VAL(YOFFS)) * VAL(YMULTS)
SIG!(I%) = LBYTE!
I% = I% + 1
SIG!(I%) = HBYTE!
IF LBYTE! > MAXVAL! THEN MAXVAL! = LBYTE!
IF HBYTE! > MAXVAL! THEN MAXVAL! = HBYTE!
IF LBYTE! < MINVAL! THEN MINVAL! = LBYTE!
IF HBYTE! < MINVAL! THEN MINVAL! = HBYTE!
INCREM2: I% = I% + 1
NEXT N%
BEEP
PRINT " Hit Any Key To Proceed"
CLOSE
WHILE INKEY$ = "": WEND
GOSUB PLOT
END
'***** EVENT QUERY RESPONSE WHEN "SRQ" *****
EVENT:
CLS
ANSWR$ = ""
PATH$ = "PATH OFF'
EVENTS = "EVENT ?"
PRINT #1, "OUTPUT 12 $ +", PATH$
PRINT #1, "OUTPUT 12 $ +", EVENT$
PRINT #1, "ENTER 12 $ +", ANSWR$
INPUT #2, ANSWR$
PRINT "SRQ Received: Status=&H "; HEX$(SPOLL%), " Event= "; ANSWR$
PRINT #1, "OUTPUT 12 $ +", "PATH ON"
RESUME
END
'***** ERROR HANDLING ROUTINE *****
ERSVC:
IF (ERR <> 68) AND (ERR <> 57) THEN PRINT "Basic Error # "; ERR; " In Line "; ERL:
STOP
INPUT #2, E$
PRINT IDV488 Driver Returned Error Number
INPUT #2, E$
PRINT E$
INPUT #2, ES
PRINT E$
STOP
", E$
152
'*"** PLOT SUBROUTINE *****
PLOT:
CLS
SCREEN 3
NUMDATA% = NUMDATA% / 2
VIEW (100, 1)-(680, 288) 1 ' USE THE WINDOW OF X=1-680, Y=1-298
LINE (1, 36)-(680, 36), B, &H1111
LINE (1, 72)-(680, 72), B, &H1111
LINE (1, 108)-(680, 108), B, &H1111
LINE (1, 144)-(680, 144), B, &H1111
LINE (1, 180)-(680, 180), B, &H1111
LINE (1, 216)-(680, 216), B, &H1111
LINE (1, 252)-(680, 252), B, &H1111
LINE (58, 1)-(58, 288), B, &H1111
LINE (116, 1)-(116, 288), B, &H1111
LINE (174, 1)-(174, 288), B, &H1111
LINE (232, 1)-(232, 288), B, &H1111
LINE (290, 1)-(290, 288), B, &H1111
LINE (348, 1)-(348, 288), B, &H1111
LINE (406, 1)-(406, 288), B, &H1111
LINE (464, 1)-(464, 288), B, &H1111
LINE (522, 1)-(522, 288), B, &H1111
WINDOW (1, MINVAL! - 1)-(NUMDATA%, MAXVAL! + 1)
LOCATE 23, 42: PRINT "TIME"
LOCATE 11, 1: PRINT "INTENSITY"
IF REP$ = "1" THEN LOCATE 2, 15: PRINT "CH1 "; CH1V$; " V/DIV"
IF REP$ = "2" THEN LOCATE 2, 15: PRINT "CH2 "; CH2V$; " V/DIV"
LOCATE 2, 45: PRINT SWEEPTIMES; " S/DIV"
LOCATE 23, 1: PRINT " SAVING THE DATA!"
FOR I% = 1 TO NUMDATA% STEP 2
HBYTE% = WAVE%(I%) / 256
LBYTE% = WAVE%(I%) - (HBYTE%) * 256
HBYTE! = (HBYTE% - VAL(YOFFS)) * VAL(YMULT$)
LBYTE! = (LBYTE% - VAL(YOHI)) * VAL(YMULTS)
PSET (I%, LBYTE!)
PSET (I% + 1, HBYTE!)
NEXT I%
'******* SAVE THE DATA *********************************
1000 :
INPUT "DO YOU WANT TO SAVE DATA TO DISK ? ", SA$
IF SA$ = "Y" OR SA$ = "y" THEN 1200 ELSE 1100
1100 :
IF SA$ = "N" OR SA$ = "n" THEN 1900 ELSE 1000
1200 :
153
INPUT "WHICH DRIVE (A: B: OR C:) ", WW$
IF WW$ = "a" OR WW$ = "A" THEN WW$ = "A:"
IF WW$ = "b" OR WW$ = "B" THEN WW$ = "B:"
IF WW$ = "c" OR WW$ = "C" THEN WW$ = "C:"
INPUT " FILE NAME ", FILE$
OPEN WW$ + FILES FOR OUTPUT AS #3
IF REP$ = "1" THEN PRINT #3, "CHANNEL 1 VOLT/DIV = "; CH1V$; " V"
IF REP$ = "2" THEN PRINT #3, "CHANNEL 2 VOLT/DIV = "; CH2V$; " V"
PRINT #3, "SWEEP TIME = "; SWEEPTIMES; " s"
IF DAS = "A" OR DAS = "a" THEN PRINT #3,
"NUMBER OF WAVEFORMS AVERAGED = "; NA%
IF PP$ = "Y" OR PP$ = "y" THEN
IF DA$ = "A" OR DA$ = "a" THEN PRINT #3,
"WAVEFORM AVERAGED PK2PK = "; AVGPK2PK!; " V"
END IF
IF PPS = "Y" OR PP$ = "y" THEN
IF DA$ = "N" OR DA$ = "n" THEN PRINT #3,
"WAVEFORM PK2PK = "; NORMPIC2PKS; " V"
END IF
IF AM$ = "Y" OR AM$ = "y" THEN
IF DA$ = "A" OR DA$ = "a" THEN PRINT #3,
"WAVEFORM AVERAGED AREA = "; AVGAREA!; " VS"
END IF
IF AM$ = "Y" OR AM$ = "y" THEN
IF DA$ = "N" OR DA$ = "n" THEN PRINT #3,
"WAVEFORM AREA = "; NORMAREA$; " VS"
END IF
IF RT$ = "Y" OR RT$ = "y" THEN
IF DA$ = "A" OR DA$ = "a" THEN PRINT #3,
"WAVEFORM AVERAGED RISETIME = "; AVGRTIME!; " S"
END IF
IF
= "Y" OR RT$ = "y" THEN
IF DA$ = "N" OR DAS = "n" THEN PRINT #3,
"WAVEFORM RISETIME = "; NORMRTIMES; " S"
END IF
PRINT #3,
PRINT #3,
PRINT #3, NUMDATA% * 2, NUMDATA% * 2
TIMEUNIT! = VAL(SWEEPTIME$) * 20 / 1024
FOR I% = 1 TO NUMDATA% * 2
PRINT #3, I% * TIMEUNIT!, SIG!(I%)
NEXT I%
CLOSE #3
1900 :
WHILE INKEY$ <> "": WEND
SCREEN 0
RETURN
'***** PEAK TO PEAK VOLTAGE MEASUREMENTS SUBROUTINE *****
154
PK2PK:
EVEFLAG% = 0
RESPOND$ = ""
EVENTS = ""
ACQUIRE2:
PRINT #1, "OUTPUT 12 $ +", "VALUE? PK2PK"
PRINT #1, "ENTER 12 $ +", RESPOND$
LINE INPUT #2, RESPOND$
IF INSTR(RESPOND$, "99e99") = 0 THEN GOTO DISP2
PRINT #1, "OUTPUT 12 $ +", "EVENT?"
PRINT #1, "ENTER 12 $ +", EVENT$
LINE INPUT #2, EVENT$
IF EVENTS <> "EVENT 269" THEN GOTO EVE2
PRINT "WAITING FOR FILL"
GOTO ACQUIRE2
DISP2: CLS : PRINT : PRINT " * * * * * The Waveform Peak To Peak Voltage Is = "; RESPONDS;
V";
*****n
NORMPK2PK$ = RESPOND$
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF'
GOTO FIN2
EVE2:
CLS : PRINT : PRINT " ***** Check the TEK-2440 Error Events Table For Event # = ";
EVENTS; " *****"
EVEFLAG% = 1
FIN2:
RETURN
'***** AREA MEASUREMENTS SUBROUTINE *****
AREA:
EVEFLAG% = 0
RESPOND$ = ""
EVENTS = ""
ACQUIRE1:
PRINT #1, "OUTPUT 12 $ +", "VALUE? AREA"
PRINT #1, "ENTER 12 $ +", RESPOND$
LINE INPUT #2, RESPOND$
IF INSTR(RESPOND$, "99e99") = 0 THEN GOTO DISP1
PRINT #1, "OUTPUT 12 $ +", "EVENT?"
PRINT #1, "ENTER 12 $ +", EVENTS
LINE INPUT #2, EVENTS
IF EVENT$ <> "EVENT 269" THEN GOTO EVE1
PRINT "WAITING FOR FILL"
GOTO ACQUIRE1
DISP1: CLS : PRINT : PRINT " ***** The Waveform Area Is = "; RESPONDS; " Vs"; "
NORMAREA$ = RESPOND$
155
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF'
GOTO FIN1
EVE1:
CLS : PRINT : PRINT "
Check the TEK-2440 Error Events Table For Event # = ";
EVENTS; " *****"
EVEFLAG% = 1
FIN1:
RETURN
'***** RISE TIME MEASUREMENTS SUBROUTINE *****
RISETIME:
EVEFLAG% = 0
RESPONDS = ""
EVENTS = ""
ACQUIRE:
PRINT #1, "OUTPUT 12 $ +", "VALUE? RISE"
PRINT #1, "ENTER 12 $ +", RESPONDS
LINE INPUT #2, RESPONDS
IF INSTR(RESPOND$, "99e99") = 0 THEN GOTO DISP
PRINT #1, "OUTPUT 12 $ +", "EVENT?"
PRINT #1, "ENTER 12 $ +", EVENTS
LINE INPUT #2, EVENTS
IF EVENTS <> "EVENT 269" THEN GOTO EVE
PRINT "WAITING FOR FILL"
GOTO ACQUIRE
DISP: CLS : PRINT : PRINT " ***** The Waveform Rise Time Is = "; RESPONDS; " s"; " *****"
NORMRTIME$ = RESPONDS
PRINT #1, "OUTPUT 12 $ +", "CURS FUNCTION:OFF'
GOTO FIN
EVE:
CLS : PRINT : PRINT " ***** Check the TEK-2440 Error Events Table For Event # = ";
EVENTS; " *****"
EVEFLAG% = 1
FIN:
RETURN
'***** TIME CURSORS SETTING SUBROUTINE *****
CURSOR:
IF OW$ = "M" OR OWS = "m" THEN
CLS : PRINT : PRINT " Set The Time Gate Then Hit Any Key When Ready!"
SG$ = INPUT$(1)
DO WHILE SG$ = ""
156
LOOP
GOTO ENDMANUAL
END IF
GETONE:
ONEPOS! = 0
TWOPOS! = 0
CLS
GOSUB SHOWCURSOR
PRINT : INPUT " Select Cursor One Vertical Position? ( 0
1023)"; ONEPOS!
IF ONEPOS! < 0 OR ONEPOS! > 1023 THEN GOTO GETONE
ONEPOSORIG! = ONEPOS!
GOSUB SHOWCURSOR
PRINT #1, "OUTPUT 12 $ +", "CURSOR TPOS:ONE:"; ONEPOS!
GETONEAG:
CLS : GOSUB SHOWCURSOR
PRINT : PRINT " Change Cursor One Position Again? (Y Or N)"
C1$ = INPUT$(1)
IF
= "N" OR C1$ = "n" THEN CLS : GOTO GETTWO
IF C1$ = "Y" OR C1$ = "y" THEN GOTO GETONE
IF CR$ = "Y" OR CR$ = "y" THEN
IF C1$ = "N" OR C1$ = "n" THEN GOTO GETTWOAG
ELSE GOTO GETONEAG
END IF
GETTWO:
CLS
GOSUB SHOWCURSOR
PRINT : INPUT " Select Cursor Two Vertical Position? ( 0
1023)"; TWOPOS!
IF TWOPOS! < 0 OR TWOPOS! > 1023 THEN GOTO GETTWO
TWOPOSORIG! = TWOPOS!
GOSUB SHOWCURSOR
PRINT #1, "OUTPUT 12 $ +", "CURSOR TPOS:TWO:"; TWOPOS!
GETTWOAG:
CLS : GOSUB SHOWCURSOR
PRINT : PRINT " Change Cursor Two Position Again? (Y Or N)"
C2$ = INPUT$(1)
IF C2$ = "Y" OR C2$ = "y" THEN GOTO GETTWO
IF C2$ = "N" OR C2$ = "n" THEN
GOTO CURSREPOS
ELSE GOTO GETTWOAG
END IF
CURSREPOS: PRINT : PRINT " Do You Want To Reposition Any Of The Two Cursors?
(Y Or N)"
CR$ = INPUT$(1)
IF CR$ = "N" OR CR$ = "n" THEN
RETURN
END IF
IF CR$ = "Y" OR CR$ = "y" THEN
157
CURSOPT: PRINT : INPUT " Cursor 1 Or 2 (1 Or 2)"; CURS$
END IF
IF CURS$ = "1" THEN CLS : GOTO GETONEAG
IF CURS$ = "2" THEN
CLS : GOTO GETTWOAG
ELSE GOTO CURSOPT
END IF
ENDMANUAL:
RETURN
'***** CURSORS POSITION SUBROUTINE
SHOWCURSOR:
VALUES = ""
UNITS$ = ""
LOCATE 1, 55: PRINT " Cursor # 1 Loc = "; ONEPOSORIG!
LOCATE 2, 55: PRINT " Cursor # 2 Loc = "; TWOPOSORIG!
PRINT #1, "OUTPUT 12 $ +", "CURSOR? DISPLAY, VALUE"
PRINT #1, "ENTER 12 $ +", VALUES
LINE INPUT #2, VALUES
PRINT #1, "OUTPUT 12 $ +", "CURSOR? DISPLAY, UNITS"
PRINT #1, "ENTER 12 $ +", UNITS$
LINE INPUT #2, UNITS$
VALUES = MID$(UNITS$, 3, 9)
IF ONEPOSORIG! = TWOPOSORIG! THEN VALUE$ = "0"
LOCATE 3, 55: PRINT " Time Window = "; VALUES; " s"
RETURN
END
158
Appendix B
Quick Basic 4.5 source codes written for Stanford research programmable
module SR245
159
,
'PROGRAM TO LOCK THE CONTINUUM YAG LASERS' FREQUENCY TO THE
'LIGHTWAVE SEEDERS' (MODEL 122) FREQUENCY. WRITIEN FOR
'STANFORD RESEARCH PROGRAMMABLE MODULE (SR245)
'"FEEDBKSR.BAS" MANSOUR ZAHEDI, AUG.10.1992, VERSION MOD. JAN. 6,1993
,
OPEN "com1:9600,n,8,2,cs,ds,cd" FOR RANDOM AS #1
'OPEN COMMUN. PORT # 1
USING RS232 TYPE COMMUN.
PRINT #1,
'CLEAR THE BUN'T'ER
PRINT #1, "MR"
'MASTER RESET
PRINT #1,
PRINT #1, 16;W0"
'SIX INPUT ANALOG CHANNELS, TWO
OUTPUT
PRINT #1,
PRINT #1, "SB2=I"
'DIGITAL CH2 = INPUT
PRINT #1,
DIM T5OSIG(4200), T5OAVG(4200), IOSIG(4200), TEMP(4200), SCANI(4200), VOLT(4200)
,
MAIN MENU
CLS
MAIN.MENU:
SCREEN 0, 0, 0
CLS
LOCATE 3, 16
COLOR 0, 7
'REVERSE VIDEO
PRINT "
MAIN MENU
"
COLOR 7, 0
'NORMAL VIDEO
PRINT
LOCATE 8, 20
PRINT "(1) SCAN THE SEEDER
"
LOCATE 10, 20
PRINT "(2) BEGIN THE FEEDBACK TO THE SEEDER
"
LOCATE 12, 20
PRINT "(3) SAVE DATA ON DISK "
LOCATE 14, 20
PRINT "(4) SR245 PROGRAMMABLE MODULE SET UP"
LOCATE 16, 20
PRINT "(5) QUIT
"
LOCATE 6, 8: PRINT CHR$(201),
'DOUBLE LINED BOX,UP LFT CORNER
LOCATE 6, 72: PRINT CHR$(187),
'DOUBLE LINED BOX,UP RT CORNER
LOCATE 18, 8: PRINT CHR$(200),
'DOUBLE LINED BOX,LOW LFT CORNER
LOCATE 18, 72: PRINT CHR$(188),
'DOUBLE LINED BOX,LOW RT CORNER
FOR I = 9 TO 71
LOCATE 6, I: PRINT CHR$(205)
LOCATE 18, I: PRINT CHR$(205)
NEXT I
FOR I = 7 TO 17
'DOUBLE LINED BOX,TOP
'DOUBLE LINED BOX,BOTTOM
160
LOCATE I, 8: PRINT CHR$(186)
LOCATE I, 72: PRINT CHR$(186)
NEXT I
LOCATE 20, 22
PRINT " MAKE YOUR CHOICE "
COLOR 0, 7
LOCATE 20, 40: PRINT " # 1-5 "
COLOR 7, 0
CHOICES = INPUT$(1)
CHOICE% = VAL(CHOICE$)
SELECT CASE CHOICE%
CASE 1: GOSUB SCAN.SEEDER
CASE 2: GOSUB LOCKSLAVE
CASE 3: GOSUB SAVE.DATA
CASE 4: GOSUB SR245.SETUP
CASE 5: GOSUB DONE
END SELECT
'DOUBLE LINED BOX,LFT SIDE
'DOUBLE LINED BOX,RT SIDE
CASE 4&5
DONE:
END
CASE 1
SEEDER SCAN SUBROUTINE
SCAN.SEEDER:
CLS
VOLTAGE = 0
GOSUB GIVEVOLT
INPUT " INPUT VOLTAGE STEP IN VOLTS, DEFAULT=0.1 V --->"; IVOLT.STEP$
IF IVOLT.STEP$ = "" THEN
VOLT.STEP = .1
VOLTSTEP = VOLT.STEP
GOTO GET.SHOTS
END IF
VOLT.STEP = VAL(IVOLT.STEP$)
VOLTSTEP = VOLT.STEP
GET.SHOTS:
INPUT " NUMBER OF SHOTS TO BE AVG'D(# SHOTS/20=INTERVAL BET. EACH V
STEP sec.)--->"; NUMSHOTS%
INPUT " ENTER THE START VOLTAGE FOR THE SCAN, (DAC RANGE = +/- 10)
DEF=0 V ---> "; IVOLTAGE$
IF IVOLTAGE$ = "" THEN
VOLTAGE = 0
ELSE VOLTAGE = VAL(IVOLTAGE,$)
POL.FLAG = 1
END IF
161
INPUT " ENTER THE END VOLTAGE FOR THE SCAN, DEFAULT=1 V --->",
IVOLT.LIMIT$
IF IVOLT.LIMIT$ = "" THEN
VOLT.LIMIT = 1
GOTO 1
END IF
VOLT.LIMIT = VAL(IVOLT.LIMIT$)
1:
INPUT " DO YOU LIKE TO NORM. CH1 (I) TO CH2 (It)) (Y OR N) - - - > "; NORM.FLAG$
IF NORM.FLAG$ = "Y" OR NORM.FLAG$ = "y" THEN
NORM.FLAG = 1
ELSEIF NORM.FLAG$ = "N" OR NORM.FLAG$ = "n" THEN
NORM.FLAG = 0
END IF
CLS : LOCATE 2, 18
COLOR 0, 7
'REVERSE VIDEO
PRINT "
SR245 PROGRAMMABLE MODULE SETTINGS
"
COLOR 7, 0
'NORMAL VIDEO
PRINT : PRINT " ANALOG CHANNELS 1,...,6 ARE INPUT. "
PRINT " ANALOG CHANNELS 7 AND 8 ARE OUTPUT. "
PRINT " CH1 = 12 SIGNAL (I)"
PRINT " CH2 = YAG SIGNAL (I0)"
PRINT " CH3 = DAC OUT FROM CH7 "
PRINT " CH4 = SEEDER CASE TEMP "
PRINT " CH7 = VOLTAGE TO SEEDER "
PRINT " CH8 = GOOD SHOTS TO APPLE "
PRINT " DIGITAL CH1 = TRIGGER, +1- 2 V, 5 mic. sec. rise time "
PRINT " DIGITAL CH2 = PIEZO RESET "
PRINT : PRINT " HIT ANY KEY TO CONTINUE! "
WHILE INKEY$ = "": WEND
GOSUB I2.SCAN
10 :
LOCATE 10, 1
INPUT "WOULD YOU LIKE TO SAVE THE DATA"; ANS$
IF ANS$ = "Y" OR ANS$ = "y" THEN
GOTO SAVE.DATA
ELSEIF ANS$ = "N" OR ANS$ = "n" THEN
GOTO MAIN.MENU
ELSE GOTO 10
END IF
GOTO MAIN.MENU
CASE 2
SLAVE LASERS' FREQUENCY LOCKING SUBROUTINE
162
LOCKSLAVE:
CLS
'
VOLTAGE = 0
GOSUB GIVEVOLT
K% = 1
NUM.RESET% = 0
NUM.BADSHOTS% = 0
INPUT "DO YOU WANT TO LET THE COMPUTER FINDS THE %50 T POINT?
(Y,N) --->", ANS$
IF ANS$ = "Y" OR ANS$ = "y" THEN
CONT.FLAG% = 1
INPUT " DO YOU LIKE TO NORM. CH1 (I) TO CH2 (JO) (Y OR N) --->"; NORM.FLAG$
IF NORM.FLAG$ = "Y" OR NORM.FLAG$ = "y" THEN
NORM.FLAG = 1
ELSEIF NORM.FLAG$ = "N" OR NORM.FLAG$ = "n" THEN
NORM.FLAG = 0
END IF
INPUT "ENTER MAX. OR MIN. VOLTAGE IN VOLTS, DEFAULT RANGE=-10 TO 10
V --->", IVOLT.LIMITS
IF IVOLT.LIMIT$ = "" THEN
VOLT.LIMIT = 10
GOTO 80
END IF
VOLT.LIMIT = VAL(IVOLT.LIMIT$)
80 :
PRINT
PRINT "SCANNING THE SEEDER, PLEASE WAIT!"
GOSUB T50.SCAN
PRINT : PRINT : CLS
PRINT "%50 TRANSMISSION SIG. = "; T50; " V"
PRINT "%100 TRANSMISSION SIG. = "; T100; " V"
PRINT "%0 TRANSMISSION SIG. = "; TO; " V"
INPUT "SCAN THE SEEDER TO THIS %50 T POINT?, OK! (Y,N) --->", ANS$
IF ANS$ = "N" OR ANS$ = "n" THEN GOTO LOCKSLAVE
90 :
INPUT "CHOOSE THE FALLING EDGE OR THE RISING EDGE OF THE 12 LINE.
(F or R) --->", ANS$
IF ANS$ = "F' OR ANS$ = T THEN
FALL.R1SE$ = "FALLING"
EDGE% = 1
ELSEIF ANS$ = "R" OR ANS$ = "r" THEN
FALL.R1SE$ = "RISING"
EDGE% = 2
ELSE GOTO 90
END IF
INPUT "WITH WHAT ACCURACY WANT THE %50 T TO BE LOCATED?
DEF.RANGE=(+/-)0.01 V --->"; SIG.FLUCT$
IF SIG.FLUCT$ = "" THEN SIG.FLUCT = .01
'SHOT-TO-SHOT FLUCT. IN SIG.
SIG.FLUCT = VAL(SIG.FLUCT$)
163
PRINT "SCANNING TO THE %50 T POINT OF THE "; FALL.RISE$; "EDGE OF THE
12 LINE, WAIT PLEASE!"
GOSUB SET.T50
IF RANGE.FLAG% = 1 THEN GOTO LOCKSLAVE
T50.ORIG = T50
'INITIAL %50 T VALUE
NORMALIZED
CLS : PRINT
PRINT "NOW SITTING AT THE 12 %50 "; FALL.RISES; "T POINT"
GOTO 100
END IF
INPUT "ENTER THE %50 T VALUE (V) --->", T50
IF T50 < 0 THEN T50 = T50 * -1
'INITIAL %50 T VALUE
T50.ORIG = T50
INPUT "ENTER THE %100 T VALUE (V) --->", T100
IF T100 < 0 THEN T100 = T100 * -1
INPUT "ENTER THE %0 T VALUE (V) --->", TO
IF TO < 0 THEN TO = TO * -1
'NORMALIZE ORIG. %50 T
' T50.ORIG = T50.ORIG / T100
INPUT "ENTER AN INITIAL VOLTAGE TO OFFSET DAC (DEFAULT= +0.0018 v)";
VOLTAGES
IF VOLTAGES = "" THEN VOLTAGE = .0018
VOLTAGE = VAL(VOLTAGE$)
CLS : PRINT "NOW SET THE YAG LASER AT THE 12 %50 T POINT"
PRINT : PRINT "HIT ANY KEY WHEN READY!"
WHILE INKEY$ = "": WEND
INPUT "IS THE FALLING EDGE OR THE RISING EDGE OF THE 12 LINE CHOSEN?
(F or R) --->", ANS$
IF ANS$ = "F' OR ANS$ = T THEN SIDE% = 1
IF ANS$ = "R" OR ANS$ = "r" THEN SIDE% = 2
100 :
'VOLTAGE = .0027
VOLTSTEP = .0005 * 2
'OFFSET COMPENSATION
'VOLTAGE/STEP
INPUT "ENTER THE BADSHOT THRESHOLD LEVEL (V) --->", TH.HOLD
IF TH.HOLD < 0 THEN TH.HOLD = TH.HOLD * -1
IF TH.HOLD > T100 THEN
BEEP
GOTO 110
ELSEIF TH.HOLD < T50 THEN
BEEP
110: PRINT "THRESHOLD OUT OF RANGE!"
GOTO 100
END IF
IF CONT.FLAG% = 1 THEN
TH.HOLD = TH.HOLD * T100
END IF
INPUT "ENTER TIME [SECONDS] INTERVAL FOR DATA STORAGE --- >", TIME.INT%
INPUT "ENTER THE NUMBER OF SHOTS TO AVERAGE --->", NUMSHOTS%
COUNTER% = (TIME.INT%) / (NUMSHOTS% / 20) 'CALCULATE A COUNTER FOR
164
THE PROPER DATA STORAGE INCREMENT
INPUT "DO YOU WANT TO COLLECT DATA ON CH2 FOR I0 TOO? %w,N)--- >", ANS$
IF ANS$ = "Y" OR ANS$ = "y" THEN ATODC% = 2
IF ANS$ = "N" OR ANS$ = "n" THEN ATODC% = 1
IF ATODC% = 1 THEN
PRINT "COLLECTING DATA ON CH1 ONLY! "
IO.PER.SHOT = 1
ELSEIF ATODC% = 2 THEN
PRINT "COLLECTING DATA ON CH1 AND CH2"
END IF
PRINT
INPUT "CHANGE ANYTHING?", ANS$
IF ANS$ = "Y" OR ANS$ = "y" THEN
GOTO LOCK.SLAVE
ELSEIF ANS$ = "N" OR ANS$ = "n" THEN
CLS : LOCATE 2, 18
COLOR 0, 7
'REVERSE VIDEO
PRINT "
SR245 PROGRAMMABLE MODULE SETTINGS
"
COLOR 7, 0
'NORMAL VIDEO
PRINT : PRINT " ANALOG CHANNELS 1,...,6 ARE INPUT. "
PRINT " ANALOG CHANNELS 7 AND 8 ARE OUTPUT. "
PRINT " CH1 = 12 SIGNAL (I)"
PRINT " CH2 = YAG SIGNAL (I0)"
PRINT " CH3 = DAC OUT FROM CH7 "
PRINT " CH4 = SEEDER CASE TEMP "
PRINT " CH7 = VOLTAGE TO SEEDER "
PRINT " CH8 = GOOD SHOTS TO APPLE "
PRINT " DIGITAL CH1 = TRIGGER, +/- 2 V, 5 mic. sec. rise time "
PRINT " DIGITAL CH2 = PIEZO RESET "
PRINT : PRINT " HIT ANY KEY TO CONTINUE! "
WHILE INKEY$ = "": WEND
CLS : PRINT "BEGIN FEEDBACK!"
LOCATE 22, 1
PRINT "HIT [0] TO QUIT. "
DISPLAY BOX ON THE SCREEN
LOCATE 6, 8: PRINT CHR$(201),
LOCATE 6, 72: PRINT CHR$(187),
LOCATE 18, 8: PRINT CHR$(200),
LOCATE 18, 72: PRINT CHR$(188),
CORNER
'DOUBLE LINED BOX,UP LFT CORNER
'DOUBLE LINED BOX,UP RT CORNER
'DOUBLE LINED BOX,LOW LFT
'CORNER
'DOUBLE LINED BOX,LOW RT
FOR I = 9 TO 71
LOCATE 6, I: PRINT CHR$(205)
LOCATE 18, I: PRINT CHR$(205)
NEXT I
'DOUBLE LINED BOX,TOP
'DOUBLE LINED BOX,BOTTOM
FOR I = 7 TO 17
LOCATE I, 8: PRINT CHR$(186)
LOCATE I, 72: PRINT CHR$(186)
NEXT I
'DOUBLE LINED BOX,LFT SIDE
'DOUBLE LINED BOX,RT SIDE
165
END IF
FEEDBACK LOOP
DO
ANS$ = INKEY$
FOR I% = 1 TO COUNTER%
SUMO = 0
SUM1 = 0
SUM2 = 0
SEED.VOLT = 0
TOTALO = 0
FOR j% = 1 TO NUMSHOTS%
CHECK FOR RESET OF THE PIEZO
REM HAVE THE RESET SIGNAL CONNECiED TO PORT AO (DPC-2 PIN#2)
PIEZO.FLAG = 0
PRINT #1, "MA"
PRINT #1,
DO
PRINT #1, "?B2"
'SET THE ASYNC. MODE
'LOOP WHILE PORT B2 IS LOW, PIEZO RESET
'READ DIG. CH2
PRINT #1,
INPUT #1, PIEZO.RESET
IF PIEZO.RESET = 1 THEN EXIT DO
LOCATE 7, 38
COLOR 0, 7
PRINT "RESET"
COLOR 7, 0
LOCATE 7, 38
COLOR 7, 0
PRINT "
"
COLOR 0, 7
PIEZO.FLAG = 1
LOOP WHILE PIEZO.RESET = 0
IF PIEZO.FLAG = 1 THEN
NUM.RESET% = NUM.RESET% + 1
END IF
'WAIT FOR THE PIEZO RESET
ADC FOR CHANNELS 1,2,3 & 4 USING SCAN FUNCTION
PRINT #1, "MS"
PRINT #1,
PRINT #1, "Tl"
PRINT #1,
PRINT #1, "SC1,2,3,4:1"
'SET SYNCH. MODE
'EACH PULSE AT DIG. CH1 BE A TRIG.
'WAIT FOR A TRIGGER, THEN SCAN DIGITIZE
'CH1,..,CH4
PRINT #1,
DO
PRINT #1, "?S"
'GET THE VOLTAGES FOR 3 CHANNELS
'IS THE TRIG. RECEIVED?
'IF NOT, WAIT.
166
PRINT #1,
INPUT #1, STATUS
LOOP UNTIL (STATUS AND 32) = 32
PRINT #1, "N"
'GET THE NEXT CHANNEL'S DIG'D
PRINT #1,
'-STORED VOLTAGE
INPUT #1, V1
PRINT #1, "N"
PRINT #1,
INPUT #1, V2
PRINT #1, "N"
PRINT #1,
INPUT #1, V3
PRINT #1, "N"
PRINT #1,
INPUT #1, V4
IF V1 < 0 THEN V1 = V1 * -1
IF V2 < 0 THEN V2 = V2 * -1
T50.PER.SHOT = V1
'READ IN %50 T VALUE FOR THE SHOT
IF ATODC% = 1 THEN 200
'SECOND A/D?
IO.PER.SHOT = V2
'READ IN I0 VALUE FOR THE SHOT
200 :
T50.NORM = T50.PER.SHOT / IO.PER.SHOT
IF TH.HOLD < 0 THEN TH.HOLD = TH.HOLD * -1
TH.HOLD.NORM = TH.HOLD / IO.PER.SHOT
BAD SHOT REJECTION
IF T50.NORM > TH.HOLD.NORM THEN
'IS IT BAD SHOT?
j% = j% - 1
NUM.BADSHOTS% = NUM.BADSHOTS% + 1
'KEEP TRACK OF THE # OF
BAD SHOTS
GOTO START.OVER
'IF SO, DO ATODC ON THE NEXT SHOT
END IF
PRINT #1, "S8=0"
'ELSE, CLEAR THE OUTPUT PORT
PRINT #1,
'SEND A GOOD SHOT TO APPLE
PRINT #1, "S8=5"
PRINT #1,
PRINT #1, "S8=0"
'RESET BACK TO ZERO
TOTALO = TOTALO + T50.PER.SHOT
SUMO = SUMO + T50.NORM
SUM! = SUM1 + IO.PER.SHOT
REM DIGITIZE DAC VOLTAGE ON CHANNEL 3
DUMMY2 = V3
'READ IN SIG. INT. VALUE FOR THE SHOT
SEED.VOLT = SEED.VOLT + DUMMY2
167
'IF I% = COUNTER% THEN
'DUM2 = V4
'SUM2 = SUM2 + DUM2
'END IF
'READ TEMP. FROM ND CHANNEL 3
'READ IN TEMP. VALUE
'COLLECT FOR ALL SHOTS
START.OVER:
NEXT j%
'%50 T AVERAGED
SUMO.AVG = TOTALO / NUMSHOTS%
'%50 T NORMALIZED
SUMO.NORM = SUMO / NUMSHOTS%
'IO NORMALIZED
SUM.AVG1 = SUM1 / NUMSHOTS%
'UPDATE AVG VALUE FOR %50 T
T50.NEW = SUMO.NORM
'IO AVG'D VALUE
IO.AVG = SUM.AVG1
SEED.VOLT.AVG = SEED.VOLT / NUMSHOTS%
'TEMPERATURE = SUM2 / NUMSHOTS%
SEND FEED BACK
IF SIDE% = 1 THEN
GOTO FALL
ELSEIF SIDE% = 2 THEN
GOTO RISE
END IF
'WHICH SIDE OF 12 LINE?
FALL:
IF T50.NEW - T50.ORIG > 0 THEN
VOLTAGE = VOLTAGE + VOLTSTEP
GOSUB GIVEVOLT
GOTO 210
ELSEIF T50.NEW - T50.ORIG < 0 THEN
VOLTAGE = VOLTAGE - VOLTSTEP
GOSUB GIVEVOLT
GOTO 210
END IF
'IF >0 => RAISE SEED FREQ.
'IF <0 => LOWER SEED FREQ.
RISE:
'IF >0 => LOWER SEED FREQ.
IF T50.NEW - T50.ORIG > 0 THEN
VOLTAGE = VOLTAGE - VOLTSTEP
GOSUB GIVEVOLT
GOTO 210
'IF <0 => RAISE SEED FREQ.
ELSEIF T50.NEW - T50.ORIG < 0 THEN
VOLTAGE = VOLTAGE + VOLTSTEP
GOSUB GIVEVOLT
GOTO 210
END IF
210 :
IF I% = COUNTER% THEN
T5OSIG(K%) = T50.NEW
'STORE THE %50 T FOR EVERY
'-TIME.INT%,[%50 T AVG'D NORM.]
168
T50AVG(K%) = SUMO.AVG
IOSIG(K%) = IO.AVG
VOLT(K%) = SEED.VOLT.AVG
'TEMP(K%) = TEMPERATURE
'%50 T SIG. AVERAGED
'STORE THE AVG'D TEMP. VALUE
K% = K% + 1
END IF
DISPLAY RESULTS ON THE SCREEN
LOCATE 3, 30
COLOR 0, 7
PRINT " NO. OF BADSHOTS "
COLOR 7, 0
LOCATE 5, 39
PRINT NUM.BADSHOTS%
LOCATE 8, 37
PRINT NUM.RESET%
LOCATE 10, 12
COLOR 0, 7
PRINT " %50 T I(AVG.)
VOLTAGE TO SEEDER
COLOR 7, 0
LOCATE 12, 16
TEMP.
"
PRINT USING "##.#####"; T50.NEW * IO.AVG
LOCATE 12, 37
PRINT USING "##.#####"; VOLT(%)
LOCATE 12, 59
PRINT USING "##.###"; TEMP(I%)
LOCATE 14, 10
COLOR 0, 7
PRINT " %50 T I(NORM.)
COLOR 7, 0
OFFSET FROM %50 T POINT
LOCATE 16, 14
PRINT USING "##.#####"; T50.NEW
LOCATE 16, 37
PRINT USING "##.#######"; T50.ORIG - T50.NEW
LOCATE 16, 60
PRINT USING "##.####"; T50.ORIG
NEXT I%
LOOP UNTIL ANS$ = "Q" OR ANS$ = "q"
500 :
LOCATE 20, 1
INPUT "WOULD YOU LIKE TO SAVE THE DATA"; ANS$
IF ANS$ = "Y" OR ANS$ = "y" THEN
GOTO SAVE.DATA
ELSEIF ANS$ = "N" OR ANS$ = "n" THEN
GOTO MAIN.MENU
ELSE GOTO 500
END IF
%50 T ORIG."
169
GOTO MAIN.MENU
SAVING DATA SUBROUTINE
SAVE.DATA:
CLS
1000 :
INPUT "DO YOU WANT TO SAVE DATA TO DISK --->? ", SA$
IF SA$ = "N" OR SA$ = "n" THEN
GOTO 1200
ELSEIF SA$ = "Y" OR SA$ = "y" THEN
GOTO 1100
ELSE GOTO 1000
END IF
1100 :
PRINT "(1) %50 T Vs. TEMP. DATA?"
PRINT "(2) IODINE SCAN Vs. VOL DATA?"
INPUT "MAKE YOUR CHOICE #1 OR 2"; CHOICES%
INPUT "WHICH DRIVE (A: B: OR C:) ", WD$
IF WD$ = "a" OR WD$ = "A" THEN WD$ = "A:"
IF WD$ = "b" OR WD$ = "B" THEN WD$ = "B:"
IF WD$ = "c" OR WD$ = "C" THEN WD$ = "C:"
INPUT " FILE NAME ", FILES
IF CHOICES% = 1 THEN
OPEN WD$ + FILE$ FOR OUTPUT AS #2
PRINT #2, "VOLT/STEP", "TIME INTERVAL"
PRINT #2, VOLTSTEP, TIME.INT%
PRINT #2, "%50 T-SIG.", "SEEDER VOLTAGE", 10 AVG", "%50 T AVG"
PRINT #2, K% 1, K% - 1, K% - 1
FOR I% = 1 TO K% - 1
PRINT #2, T5OSIG(I%), VOLT(I%), IOSIG(I%), T50AVG(I%)
NEXT I%
ELSEIF CHOICES% = 2 THEN
OPEN WD$ + FILE$ FOR OUTPUT AS #3
PRINT #3, "SEDDER VOLTAGE", "12 SIG. INT.", 10 AVG"
PRINT #3, I2.COUNTER%, I2.COUNTER%
FOR I% = 1 TO I2.COUNTER% - 1
PRINT #3, VOLT(I%), SCANI(I%), IOSIG(I%)
NEXT I%
END IF
CLOSE #1
CLOSE #2
CLOSE #3
1200 :
GOTO MAIN.MENU
END
GIVEVOLT SUBROUTINE
GIVEVOLT:
170
I=7
FORMAT$ = "S#=##.#####"
'DAC OUTPUT CHANNEL #
'SEND OUT THE VOLTAGE TO
PRINT #1, USING FORMAT$; I; VOLTAGE
SEEDER
PRINT #1,
RETURN
TIME INTERVAL SUBROUTINE
INTERVAL:
CON = &H43
T2 = &H42
TEST = &HB4
ENAB = &H61
FASTTICKS& = 11925
TIMEHI& = FASTTICKS \ 256
TIMELOW& = FASTTICKS& - TIMEHI& * 256
LATCHBYTE = &H80
OUT CON, TSET
OUT T2, TIMELO&
OUT T2, TIMEHI&
OLDPPI = INP(ENAB)
PPI = OLDPPI OR 1
OUT ENAB, PPI
NEW& = FASTTICKS&
FOR TICKSTHISINTERVAL = 1 TO NTIME%
DO
SPLIT: OLD& = NEW&
OUT CON, LATCHBYTE
NEWLO& = INP(T2)
NEWHI& = INP(T2)
NEW& = NEWHI& * 256 + NEWLO&
LOOP WHILE NEW& < OLD&
NEXT TICKSTHISINTERVAL
OUT ENAB, OLDPPI
RETURN
SUBROUTINE TO SCAN THE SEEDER AND
DETERMINE %50 T, %0 T & %100 T SIGNAL VALUES
T50.SCAN:
VOLT.STEP = .02 / 4
VOLTSTEP = VOLT.STEP
I2.VOLTS'TEP = VOLTSTEP
VOLTAGE = 0
GOSUB GIVEVOLT
I2.COUNTER% = VOLT.LIMIT / VOLTSTEP
NUMSHOTS% = 40
'.05 V/STEP, 2 s/STEP
171
FOR I% = 1 TO I2.COUNTER%
I2.SIG.SUM = 0
SEED.VOLT = 0
VOLTAGE = VOLTAGE + VOLTSTEP
SHOW.VOLT = SHOW.VOLT + VOLT.STEP
'INCREMENT THE VOLTAGE
IF VOLTAGE > VOLT.LIMIT THEN
GOTO RANGE1
ELSEIF VOLTAGE < -VOLT.LIMIT THEN
GOTO RANGE1
END IF
GOSUB GIVEVOLT
FOR j% = 1 TO NUMSHOTS%
CHECK FOR RESET OF THE PIEZO
PRINT #1, "MA"
PRINT #1,
DO
PRINT #1, "?B2"
PRINT #1,
INPUT #1, PIEZO.RESET
LOOP WHILE PIEZO.RESET = 0
'SET THE ASYNC. MODE
'LOOP WHILE PORT B2 IS LOW, PIEZO RESET
'READ DIG. CH2
'WAIT FOR THE PIEZO RESET
ADC FOR CHANNELS 1,2 & 3 USING SCAN FUNCTION
PRINT #1, "MS"
PRINT #1,
PRINT #1, "Tl"
PRINT #1,
PRINT #1, "SC1,2,3:1"
'SET SYNCH. MODE
'EACH PULSE AT DIG. CH1 BE A TRIG.
'WAIT FOR A TRIGGER, THEN SCAN DIGITIZE
'CH1,..,CH4
PRINT #1,
DO
'GET THE VOLTAGES FOR 3 CHANNELS
'IS THE TRIG. RECEIVED?
'IF NOT, WAIT.
PRINT #1, "?S"
PRINT #1,
INPUT #1, STATUS
LOOP UNTIL (STATUS AND 32) = 32
PRINT #1, "N"
'GET THE NEXT CHANNEL'S DIG'D
PRINT #1,
'-STORED VOLTAGE
INPUT #1, V1
PRINT #1, "N"
PRINT #1,
INPUT #1, V2
PRINT #1, "N"
PRINT #1,
INPUT #1, V3
IF V1 < 0 THEN V1 = V1 * -1
IF V2 < 0 THEN V2 = V2 * -1
DUMMYO = V1
'READ IN SIG. INT. VALUE FOR THE SHOT
172
DUMMY1 = V2
'READ IN SIG. INT. VALUE FOR THE SHOT
12.SIG.NORM = DUMMYO / DUMMY1
'NORMALIZE THE 12 SIG. TO THE
I0
I2.SIG.SUM = I2.SIG.SUM + I2.SIG.NORM 'ADD FOR ALL SHOTS
IF NORM.FLAG = 1 THEN
12.SIG.NORM = DUMMYO / DUMMY1
'NORMALIZE THE 12 SIG. TO
THE I0
I2.SIG.SUM = I2.SIG.SUM + I2.SIG.NORM 'ADD FOR ALL SHOTS
ELSEIF NORM.FLAG = 0 THEN
I2.SIG.SUM = I2.SIG.SUM + DUMMYO
'ADD FOR ALL SHOTS
END IF
DUMMY2 = V3
'READ IN SIG. INT. VALUE FOR THE SHOT
SEED.VOLT = SEED.VOLT + DUMMY2
NEXT j%
SCANI(I %) = I2.SIG.SUM / NUMSHOTS%
VOLT(I %) = SEED.VOLT / NUMSHOTS%
LOCATE 5, 16
COLOR 0, 7
PRINT " SEEDER VOLTAGE
SIGNAL INT. (NORM.)
COLOR 7, 0
LOCATE 7, 21
"
PRINT USING "##.#####"; VOLT(I%)
LOCATE 7, 50
PRINT USING "##.#####"; SCANI(I %)
NEXT I%
RANGE1:
BEEP
VOLTAGE = 0
GOSUB GIVEVOLT
VOLT.T50 = 0
VOLT.T100 = VOLT(1)
'DAC VOLTAGE AT %100 T POINT
VOLT.TO = VOLT(1)
'DAC VOLTAGE AT %0 T POINT
T100 = SCANI(1)
'SIG. INT. FOR %100 T PT
TO = SCANI(1)
'SIG. INT. FOR %0 T PT
FOR I% = 1 TO I2.COUNTER% - 1
IF SCANI(I%) > T100 THEN
'FIND THE SIGNAL MAXIMUM
T100 = SCANI(I%)
'%100 T SIGNAL=MAX.
VOLT.T100 = VOLT(I %)
ELSEIF SCANI(I %) < TO THEN
'FIND THE SIGNAL MINIMUM
TO = SCANI(I %)
'%0 T SIGNAL=MIN.
173
VOLT.TO = VOLT(I%)
END IF
NEXT I%
T50 = TO + (T100 - TO) / 2
'I SIG. FOR %50 T POINT
RETURN
SUBROUTINE TO SCAN THE SEEDER
TO THE 50% TRANSMISSION POINT OF THE IODINE LINE
SET.T50:
WE SCAN FROM LOW TO HIGH FREQUENCY AS WE INCREASE THE
REM VOLTAGE
REM
REM
REM
WHICH IS SENT TO THE SEEDER, AND WE GO THROUGH THE FALLING
EDGE OF THE 12 DOPPLER BROADENED LINE FIRST.
FOR I% = 1 TO I2.COUNTER% - 1
IF SCANI(I%) <= T50 + SIG.FLUCT THEN
IF SCANI(I%) > = T50 - SIG.FLUCT THEN
VOLT.T50 = VOLT(I%)
GOTO VOLT.CAL
END IF
END IF
NEXT I%
300 :
PRINT "COULDN'T LOCATE THE %50 T "; FALL.R1SE$; " POINT SUCCESSFULLY!"
310 :
INPUT "THE SHOT-TO-SHOT FLUC. RANGE TOO SMALL! CHANGE IT OR QUIT
[C OR Q] --->"; ANS$
IF ANS$ = "Q" OR ANS$ = "q" THEN
VOLTAGE = 0
RANGE.FLAG% = 1
ELSEIF ANS$ = "C" OR ANS$ = "c" THEN
INPUT "NEW FLUCT. RANGE VALUE(V) --->"; SIG.FLUCT
VOLTAGE = 0
GOSUB GIVEVOLT
GOTO SET.T50
ELSE GOTO 310
END IF
VOLT.CAL:
IF VOLT.T50 > VOLT.TO THEN
VOLT.T50.RISE = VOLT.T50
ELSEIF VOLT.T50 < VOLT.TO THEN
VOLT.T50.FALL = VOLT.T50
END IF
174
IF VOLT.T50.RISE = 0 THEN
VOLT.T50.RISE = VOLT.TO + (VOLT.TO - VOLT.T50.FALL)
ELSEIF VOLT.T50.FALL = 0 THEN
VOLT.T50.FALL = VOLT.TO - (VOLT.T50.RISE - VOLT.TO)
END IF
IF EDGE% = 1 THEN
VOLTAGE = VOLT.T50.FALL
ELSEIF EDGE% = 2 THEN
VOLTAGE = VOLT.T50.RISE
END IF
GOSUB GIVEVOLT
NTIME% = 60 * 5
GOSUB INTERVAL
'SET THE SEEDER AT %50 T POINT
RETURN
,
SUBROUTINE TO SCAN THE SEEDER
I2.SCAN:
I2.VOLTSTEP = VOLTSTEP
IF POL.FLAG = 1 THEN
VOLTAGE = VAL(IVOLTAGE$)
GOSUB GIVEVOLT
CLS : PRINT : PRINT " WAITING FOR THE SEEDER TO RECOVER!
HIT ANY KEY WHEN READY"
WHILE INKEY$ = "": WEND
CLS : PRINT : PRINT " SCANNING THE SEEDER, PLEASE WAIT!"
I2.COUNTER% = (ABS(VOLTAGE) + VOLT.LIMIT) / VOLTSTEP
ELSEIF POL.FLAG = 0 THEN
VOLTAGE = 0
I2.COUNTER% = VOLT.LIMIT / VOLTSTEP
GOSUB GIVEVOLT
END IF
FOR I% = 1 TO I2.COUNTER%
SUM1 = 0
I2.SIG.SUM = 0
SEED.VOLT = 0
VOLTAGE = VOLTAGE + VOLTSTEP
'INCREMENT THE VOLTAGE
IF VOLTAGE > VOLT.LIMIT THEN
GOTO RANGE2
ELSEIF VOLTAGE < -VOLT.LIMIT THEN
'
GOTO RANGE2
END IF
GOSUB GIVEVOLT
FOR j% = 1 TO NUMSHOTS%
CHECK FOR RESET OF THE PIEZO
175
PRINT #1, "MA"
PRINT #1,
DO
PRINT #1, "?B2"
PRINT #1,
INPUT #1, PIEZO.RESET
LOOP WHILE PIEZO.RESET = 0
'SET THE ASYNC. MODE
'LOOP WHILE PORT B2 IS LOW, PIEZO RESET
'READ DIG. CH2
'WAIT FOR THE PIEZO RESET
ADC FOR CHANNELS 0 USING EXT. START FUNCTION
PRINT #1, "MS"
PRINT #1,
PRINT #1, "Ti"
PRINT #1,
PRINT #1, "SC1,2,3:1"
'SET SYNCH. MODE
'EACH PULSE AT DIG. CH1 BE A TRIG.
'WAIT FOR A TRIGGER, THEN SCAN DIGITIZE
'CH1,..,CH4
PRINT #1,
DO
'GET THE VOLTAGES FOR 3 CHANNELS
'IS THE TRIG. RECEIVED?
'IF NOT, WAIT.
PRINT #1, "?S"
PRINT #1,
INPUT #1, STATUS
LOOP UNTIL (STATUS AND 32) = 32
PRINT #1, "N"
'GET THE NEXT CHANNEL'S DIG'D
PRINT #1,
'-STORED VOLTAGE
INPUT #1, V1
PRINT #1, "N"
PRINT #1,
INPUT #1, V2
PRINT #1, "N"
PRINT #1,
INPUT #1, V3
IF V1 < 0 THEN V1 = V1 * -1
IF V2 < 0 THEN V2 = V2 * -1
DUMMY() = V1
'READ IN SIG. INT. VALUE FOR THE SHOT
ADC FOR CHANNELS 1,2 & 3 USING SCAN FUNCTION
DUMMY1 = V2
'READ IN SIG. INT. VALUE FOR THE SHOT
SUM1 = SUM1 + DUMMY1
IF NORM.FLAG = 1 THEN
I2.SIG.NORM = DUMMY() / DUMMY1
'NORMALIZE THE 12 SIG.
'TO THE IO
I2.SIG.SUM = I2.SIG.SUM + I2.SIG.NORM 'ADD FOR ALL SHOTS
ELSEIF NORM.FLAG = 0 THEN
I2.SIG.SUM = I2.SIG.SUM + DUMMY()
'ADD FOR ALL SHOTS
END IF
176
'READ IN SIG. INT. VALUE FOR THE SHOT
DUMMY2 = V3
SEED.VOLT = SEED.VOLT + DUMMY2
NEXT j%
SCANI(I%) = I2.SIG.SUM / NUMSHOTS%
VOLT(I%) = SEED.VOLT / NUMSHOTS%
IOSIG(I%) = SUM1 / NUMSHOTS%
LOCATE 5, 16
COLOR 0, 7
PRINT " SEEDER VOLTAGE
SIGNAL INT. (NORM.)
COLOR 7, 0
LOCATE 7, 21
"
PRINT USING "##.#####"; VOLT(I%)
LOCATE 7, 50
PRINT USING "##.#####"; SCANI(I%)
NEXT I%
VOLTAGE = 0
GOSUB GIVEVOLT
RANGE2:
BEEP
VOLTAGE = 0
GOSUB GIVEVOLT
RETURN
'SUBROUTINE TO CHECK THE ANALOG TO DIGITAL CONVERSION FOR
'THE SR245 PROGRAMMABLE STANFORD RESEARCH MODULE; AVERAGE IN
'ADC IS POSSIBLE. MANSOUR ZAHEDI,JAN. 7,1993
SR245.SETUP:
GOSUB A.TO.D:
GOTO MAIN.MENU
A.TO.D:
CLS
DIM DUM(10)
PRINT #1, "MR"
PRINT #1, "I8;W25"
CLS
INPUT " WOULD YOU LIKE TO AVERAGE THE SIGNALS IN THE ADC CHANNELS ";
ANS$
IF ANS$ = "Y" OR ANS$ = "y" THEN
177
INPUT " NUMBER OF SHOTS TO BE AVERAGED "; NUM%
END IF
IF ANS$ = "N" OR ANS$ = "n" THEN NUM% = 1
CLS
LOCATE 1, 1
PRINT "HIT [Q] TO QUIT!"
11 :
FOR I = 1 TO 10
DUM(I) = 0
NEXT I
ANS$ = INKEY$
IF ANS$ = "Q" OR ANS$ = "q" THEN GOTO 12
FOR K% = 1 TO NUM%
FOR I = 1 TO 8
PRINT #1, USING "?#"; I
PRINT #1,
INPUT #1, V
DUM(I) = DUM(I) + V
IF K% = NUM% THEN
FOR L% = 1 TO 8
LOCATE L% + 2, 1
PRINT "CHANNEL"; USING " # = "; L%
LOCATE L% + 2, 13
PRINT USING "##.###"; DUM(L%) / NUM%
NEXT L%
END IF
NEXT I
NEXT K%
PRINT "loop count=", j
j=j+1
GOTO 11
12 :
RETURN
END
178
Appendix C
CARS studies in the low frequency rotational region
179
In an effort to obtain the pure rotational spectrum of CH3 radicals a
modification to the present CARS set up was necessary. To accomplish this the
following arrangement was made. The ring dye laser which operated with the
DCM dye at -630 nm and was pulse amplified with our Nd:YAG laser at 532 nm
in a 4 stage pulse amplifier chain served as the CARS pump beam. The output of
a Coherent single mode single frequency Kr+ laser at 647.2 nm was also pulse
amplified in a new 3 stage pulse amplifier chain by splitting another portion of the
YAG laser for this new chain. This beam served as the CARS probe beam. The
third CARS beam was the green output of the YAG laser and therefore the antiStokes signal was generated at a wavelength near 532 nm. The scattered photons
from the pump and probe beams could easily be discriminated against by using a
monochromator since they were spectrally separated from the green.
The
scattered green photons were eliminated by locking the YAG laser to one of the
12 absorption transitions near the YAG laser gain maximum and an I2 vapor cell
was used in the signal path to absorb the unwanted green photons. A schematic
diagram of this new setup is illustrated in Figure C-1.
This arrangement for the study of low frequency Raman shifts worked well.
In Figure C-2 a spectrum of CH3I in the u1 C-I symmetric stretching region at
524.6 cm-1 is illustrated. In figure C-3 a survey scan of air is shown which includes
rotational transitions both from N2 and 02. This trace was obtained by running
the dye laser with a resolution of 625 MHz with only 2 laser pulses averaged per
180
data point. Finally shown in Figure C-4 is a pure rotational spectrum of neat
CH3I at X/D = 1 in a jet with a scan down to 0 cm -1 shift.
Figure C-5 is a calculated CH3 pure rotational spectrum using a Boltzmann
distribution at a temperature of 650 K and including the hot band transition
contributions. Using this calculated spectrum as a guide, and the C-I stretch of
CH3I for optimizing beam overlaps, many scans were taken in the 100-300 cm-1
region but no conclusive sign for any CH3 transition was seen. This was attributed
to the rapid dilution of rotational population as the high translational energy of the
radicals was collisionally converted to internal energy.
An experiment was
designed to illustrate this fact. Nitrogen was mixed with the CH3I and with the
U.V. beam blocked, a scan of several N2 pure rotational transitions was made at
X/D = 2 in the jet. The U.V. beam was then introduced to dissociate the CH3I
and the same scans were repeated. Due to collisional heating of the N2 with the
CH3 radicals, the low J transitions dramatically lost intensity while the high J states
gained
intensity, as shown in Figures C6-C8.
This rapid spread of state
population is known to occur for CH3 (from our vibrational results, chapter V)
and will make detection of CH3 more difficult. In addition, it may well be that the
inherent Raman anisotropy, which determines the cross section, is small for CH3
radical (i.e. the radical is more "spherical" than CH3I, N2 or 02).
181
Single-mode
Ai laser
ring dye laser
Pulse
Integrator
Z74
'
I2cell
Single-mode
647 nm
fitter
I PMT
Kr+ laser
Chopper
V
Mono-
Sample
cell
chromator
Seeded single-mode
0L.
Nd:YAG laser
532 nm
V
OD 0-0
0000
Dye amplifier
Figure C-1. O.S.U. new high resolution pure rotational experimental setup.
182
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
523.80 524.20 524.60 525.00 525.40 525.80 526.20 526.60 527.00
WAVENUMBERS
Figure C-2. Q-branch CARS spectrum of u1 C-I symmetric stretch of neat
CH3I in a free jet expansion at X/I3 = 1.
183
-10
IIIIIIIIIIIIIII
10
30
50
70
90
110
130
150
WAVENUMBERS
Figure C-3. Pure rotational scan of air (1 Atm.). Dye laser resolution was 625
MHz and 2 laser shots were averaged.
184
S-
I
-2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
0
I
2
I
I
6
1
I
I
10
I
I
14
1
18
I
1
22
I
26
WAVENUMBERS
Figure C-4. CH3I pure rotational jet spectrum. Neat sample of 400 Torr
pressure and at X/D = 0.5.
185
1
il
h,
1
0
100
200
300
400
WAVENUMBERS
Figure C-5. Simulation of CH3 pure rotational spectrum, transitions due to the
u2 hot band are also included in the calculation.
186
2800
2400 -
U.V. off
2000 -
1600 -
1200 -
800 U.V. 0
400 -
0
1
63.61
63.63
63.65
63.67
WAVENUMBERS
Figure C-6. Pure rotational jet spectrum of line S7 of N2 used as a driving gas
for CH3I. The experiment was done at X/D = 2 with the N2 pressure of 3 atm
and CH3I pressure of 400 Torr.
187
o
1
71.54
71.56
1
1
71.58
1
71.60
1
71.62
71.64
WAVENUMBERS
Figure C-7. Pure rotational jet spectrum of line S8 of N2 in jet. Same
conditions as the spectrum in Figure C-4.
188
I
103.30
I
103.32
i
I
I
103.34
I
103.36
1
103.38
WAVENUMBERS
Figure C-8. Pure rotational jet spectrum of line S12 of N2. Same conditions
as the spectrum in Figure C-4.