Rotational Spectra of pentafluorotoluene
and chloropentafluorobenzene
June 23, 2009
Ashley A. Osthoff, John Sexton, Rebecca A. Peebles and Sean A. Peebles
Department of Chemistry, Eastern Illinois University
Garry S. Grubbs II and Stephen A. Cooke,
Department of Chemistry, University of North Texas
Brooks H. Pate, Justin L. Neill and Matt T. Muckle
Department of Chemistry, University of Virginia
1
Introduction
b
a
a
Pentafluorotoluene (PFTOL)
b
Chloropentafluorobenzene (CPFB)
Want to create pentafluorobenzyl radical
3,3,3-trifluoropropyne
Comparison of CPFB with PFTOL
2
Experimental
•
FTMW spectrometer used for
pentafluorotoluene with an
axial nozzle configuration
•
Chirped-pulse broadband
microwave spectrometers
used for both
chloropentafluorobenzene
and pentafluorotoluene
•
PFTOL measured at
the University of North
Texas
•
CPFB measured at the
University of Virginia
•
Structures predicted using ab
initio[1] MP2 calculations with
a 6-311++G(2d,2p) basis set
•
SPFIT[2] and SPCAT[2] used
to predict and assign spectra
FTMW spectrometer at Eastern Illinois University
[1] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, et. al, Gaussian, Inc.,
Wallingford CT, 2004.
[2] Pickett, H. M. J. Mol. Spectrosc. 1991, 148, 371
.
3
Experimental - Chirped-Pulse Broadband
Spectrometers
Schematic of instrument located
at University of North Texas
Schematic of Instrument located
at University of Virginia
Center freq.: 8990 MHz
Bandwidth: 1515 MHz
Lorch 13EZ5 – 8990/1515 - 5
Bandpass
filter
PFTOL
8-18 GHz in four 3 GHz steps
He/Ne, 1.5 – 2 atm flowed over liquid sample
CPFB
7 - 18
7-9
GHz
GHz
range,
range
8.4
in million
one step
averages
3 nozzles,chirp
Lowered
320ktoaverages
6.8 – 9 GHz
He/Ne flowed over a liquid sample
4
Chloropentafluorobenzene – Acquiring the
spectrum
63,3 – 53,2 Transition
13C
1
87
transition
Narrow broadband region
87
Perpendicular nozzle
Broad spectrum spanning 11 GHz
76
54
65
76
Perpendicular nozzle
76
87
8158
65
8160
Purple = F + ½
54
X Axis Title
Frequency
(MHz)
65
8155
8162
Frequency (MHz)
54
8169
8155
8160
Frequency
(MHz)
X Axis Title
8165
5
Pentafluorotoluene – Spectrum
measurement
• A lot of lines found at very high intensity, including many transitions
grouped together
• Highest J values measured on the EIU FTMW instrument from a Qbranch found in the spectrum
• Small reproducible splittings seen, possibly from internal rotation
• Many unassigned lines present, probably from torsionally excited
states
6
Pentafluorotoluene – Transition grouping
105,5 – 96,4
PFTOL
Axial nozzle
200 shots
114,7 – 105,6
123,9 – 114,8
132,11 – 123,10
141,13 – 132,12
150,15 – 141,14
16023.6 16023.7 16023.8 16023.9
16024 16024.1 16024.2 16024.3 16024.4 16024.5 16024.6
Frequency (MHz)
7
Pentafluorotoluene – Spectrum
measurement
• A lot of lines found at very high intensity, including many transitions
grouped together
• Highest J values measured on the EIU FTMW instrument from a Qbranch found in the spectrum
• Small reproducible splittings seen, possibly from internal rotation
• Many unassigned lines present, probably from torsionally excited
states
8
Q-Branch
127,5 – 126,6
PFTOL
Axial nozzle
5000 shots
116,5 – 115,6
105,5 – 104,6
138,5 – 137,6
94,5 – 93,6
83,5 – 83,6
149,5 – 148,6
72,5 – 72,4
1510,5 – 159,6
5683
5683.5
61,5 – 60,6
5684
5684.5
Frequency (MHz)
5685
5685.5
5686
9
Pentafluorotoluene – Spectrum
measurement
• A lot of lines found at very high intensity, including many transitions
grouped together
• Highest J values measured on the EIU FTMW instrument from a Qbranch found in the spectrum
• Small reproducible splittings seen, possibly from internal rotation
• Many unassigned lines present, probably from torsionally excited
states
10
Pentafluorotoluene – Unexplained splitting
Axial nozzle
200 shots
55,0 – 44,1 transition showing Doppler
splitting with additional splitting seen
consistently throughout the spectrum
13953.8985 MHz
13953.8221 MHz
Axial nozzle
300 shots
10827.7873 MHz
10827.7442 MHz
10827.8029 MHz
10827.7288 MHz
13953.5
13953.6
13953.7
13953.8
13953.9
13954
13954.1
13954.2
Frequency (MHz)
Small splittings
around 16 kHz
85,3 – 76,2 Transition showing Doppler
splitting
10827.4
10827.5
10827.6
10827.7
10827.8
Frequency (MHz)
10827.9
10828
10828.1
11
Pentafluorotoluene – Spectrum
measurement
• A lot of lines found at very high intensity, including many transitions
grouped together
• Highest J values measured on the EIU FTMW instrument from a Qbranch found in the spectrum
• Small reproducible splittings seen, possibly from internal rotation
• Many unassigned lines present, probably from torsionally excited
states
12
Pentafluorotoluene – Torsional States
* = unassigned lines
*
with fast 1st order Stark
effects
*
*
*
900
10700
960
1020
10820
1080
X Axis Title
Frequency
(MHz)
1140
10940
1200
13
Pentafluorotoluene - Spectroscopic
Parameters
Fit using an S-reduction in the IIIL representation
Parameter
Normal
13C
1
13C
2
13C
3
13C
6
13C
7
MP2
A (MHz)
1036.61221(15)
1036.0730(6)
1035.9359(6)
1032.0932(3)
1032.7466(3)
1030.9420(5)
1035.2
B (MHz)
1030.94086(16)
1027.6045(6)
1027.6092(6)
1030.9721(3)
1030.9778(5)
1018.2450(2)
1021.4
C (MHz)
516.92066(11)
515.94741(13)
515.91572(11)
515.80248(10)
515.96732(10)
512.31292(9)
515.8
DJ (MHz)
19.9(16)
19.9*
19.9*
19.9*
19.9*
19.9*
---
DJK (MHz)
-30.5(41)
-30.5*
-30.5*
-30.5*
-30.5*
-30.5*
---
DK (MHz)
12.4(27)
12.4*
12.4*
12.4*
12.4*
12.4*
---
N
84
13
16
16
16
17
---
Δνrms (kHz)
3.70
0.96
1.80
1.39
5.15
2.67
---
κ
0.9782
0.9674
0.9680
0.9957
0.9932
0.9510
* -- Distortion constants fixed to value from normal species
14
Chloropentafluorobenzene- nuclear
quadrupole moment
Overlapping 81,8 – 717 &
80,8 – 70,7
72,6 – 62,5
CPFB
Perpendicular
nozzle
Purple = F + ½
54
• Despite unresolved splittings, we
were able to fit 217 components
for the normal and 90
components for the 37Cl
65
7382
• Hyperfine structure due to
characteristic quadrupole
splittings was apparent
7384
7386
Frequency (MHz)
15
Chloropentafluorobenzene-Spectroscopic
Parameters
Fit using an S-reduction in the IR representation
Parameter
Normal
37Cl
13C
1
13C
2
13C
3
13C
6
MP2
A (MHz)
1028.5412(2)
1028.5439(7)
1025.5716(19)
1025.5627(19)
1028.5783(19)
1028.568(2)
1025.3
B (MHz)
751.82072(17)
734.47954(18)
751.6505(4)
750.7696(4)
748.7217(4)
750.4372(4)
748.3
C (MHz)
434.3531(3)
428.5081(2)
433.7654(4)
433.4701(4)
433.3233(4)
433.8980(5)
432.6
DJ (Hz)
3.8(10)
3.8*
3.8*
3.8*
3.8*
3.8*
--
d1 (Hz)
3.4(9)
3.4*
3.4*
3.4*
3.4*
3.4*
--
3/2caa (MHz)
-119.278(16)
-94.00(3)
-119.17(8)
-119.15(8)
-119.26(10)
-119.5(8)
-112.94
1/4cb-c (MHz)
1.918(5)
1.53(2)
1.92(3)
1.94(3)
1.92(3)
1.91(3)
1.94
caa (MHz)
-79.52(2)
-62.67(2)
-79.45(5)
-79.43(5)
-79.51(7)
-79.7(5)
-75.29
cbb (MHz)
43.6(1)
34.39(1)
43.56(3)
43.60(3)
43.59(3)
43.7(2)
41.53
ccc (MHz)
35.92(2)
28.27(4)
35.89(9)
35.84(9)
35.91(9)
36.0(3)
33.76
κ
0.0686
0.0198
0.0743
0.0718
0.0597
0.0646
–
N
217
87
45
36
33
31
--
Δνrms (kHz)
6.1
5.5
4.9
4.1
5
4.8
--
16
* -- Distortion constants fixed to value from normal species
Pentafluorotoluene – Stark Effects
y = 3.77207E-04x - 5.49822E-02
Some transitions moved
very rapidly, others moved
very slowly
2
R = 9.51659E-01
y = 1.31378E-04x - 1.03695E-03
1
Both
which uses
perturbation theory, and
QSTARK[4], which uses an
exact calculation, determined
the dipole moment
2
R = 9.99851E-01
0.5
Delta Nu
ASYSPEC[3],
44,0 - 33,1
0
-0.5
y = 3.19790E-05x - 1.06785E-03
y = -9.43580E-06x - 3.32029E-04
2
R = 9.99955E-01
2
R = 9.98806E-01
-1
-1.5
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
E^2
33,1 - 22,0
1
y = 1.87154E-05x + 4.61782E-03
R2 = 9.87960E-01
0.5
Delta Nu
0
-0.5
y = -1.33146E-04x + 5.08960E-03
[3] Second-order Stark coefficients were computed with use
of the University of Michigan modified version of the original
ASYSPEC code, Beaudet, R. A., Ph.D. Thesis, Harvard
University, 1961.
R2 = 9.96519E-01
-1
-1.5
-2
0
2000
4000
6000
8000
10000
E^2
12000
14000
16000
18000
20000
[4] Kisiel, Z.“PROSPE–Programs for Rotational Spectroscopy”
17
available at http://info.ifpan.edu.pl/~kisiel/prospe.htm,
accessed June 2009.
Pentafluorotoluene – Dipole Moment
Dipole fits
J'
K'
K'
J"
K"
K"
M
Field (V/cm)
Obs (MHz)
Obs-Calc (MHz)
4
4
4
4
4
4
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
2
2
2
2
0
0
0
0
0
0
1
1
1
0
36
68.8
101.7
134.5
167.3
0
36
68.8
101.7
0
36
49.1
68.8
0
36
49.1
68.8
82
101.7
0
36
49.1
8770.721
8770.7042
8770.6768
8770.6251
8770.555
8770.4527
8770.721
8770.76
8770.8717
8771.0506
8770.7182
8770.885
8771.0356
8771.3484
5702.799
5702.822
5702.8515
5702.9003
5702.9195
5702.9873
5702.799
5702.6427
5702.4767
-0.00106
-0.00792
-0.00887
-0.01761
-0.02823
-0.05454
-0.00106
0.00263
0.02043
0.04699
-0.00386
-0.00803
-0.00523
0.00113
-0.00039
-0.00175
0.00668
0.01172
-0.00633
-0.00655
-0.00039
0.00866
-0.01440--
Dipole moment fits (Debye)
2.199(12)
2.161(13)
2.132(6)
2.07(2)
Current dipole
determination:
1.976(11) Debye
ab initio value:
2.17 Debye
1.99(4)
1.988(18)
2.00(3)
18
Chloropentafluorobenzene – Dipole
moment
• Dipole moment of this molecule is currently a work in progress
• Transitions very weak using FTMW spectrometer, making Stark
effect measurements difficult. Measuring high J’s making this
even more difficult
• The few transitions that are strong move very slowly
• Currently one transition has been measured that agrees with ab
initio calculations: 42,2 – 32,1, M = 0; 0.401(15) Debye (ab initio
= 0.415 Debye)
19
Pentafluorotoluene – Structure
StrfitQ[5] used for ro structure
KRA[6] and EVAL[6] used for rs structure
Distances (Å)
Angles (°)
b
1.406(17)
1.449(13)
1.401(3)
1.392
IA and IC used to assign ro structure
1.504(12)
1.504(10)
1.510(2)
1.5023
7
115.8(8)
115.5(3)
116.6
6
a
5
4
3
2
1.372(17)
1.354(12)
1.347(3)
1.390
122.6(12)
122.6(10)
123.7(4)
122.5
122.1(4)
120.8(14)
121.7
120.2(12)
119.9(10)
119.9(3)
119.4
1
119.0(8)
118.7(2)
119.9
1.396(14)
1.395(13)
1.397(2)
1.390
Key:
[5] Schwendeman, R. H. In Critical Evaluation of Chemical and Physical Structural
Information; Lide, D. R., Paul, M. A., Eds.; National Academy of Sciences:
Washington, DC, 1974. The STRFITQ program used in this work is the University
of Michigan modified version of Schwendeman's original code.
Green = 1st ro structure
Blue = 2nd ro structure
Black = rs structure
Red = ab initio values
[6] Kraitchman coordinates and propagated errors in
parameters calculated using the KRA and EVAL code,20
Kisiel, Z. PROSPE–Programs for Rotational
Spectroscopy; http://info.ifpan.edu.pl/~kisiel/prospe.htm,
accessed July 2006.
Chloropentafluorobenzene-Structure
IB and IC used to assign ro structure
Distances (Å)
1.391(8)
1.389(3)
1.397(3)
1.394
b
Angles (°)
a
1.716(5)
1.7212(18)
1.7206
116.6(3)
117.5(3)
118.7
120.5(2)
121.0(3)
120.7
61
35
4
2
3
5
2
4
1.383(5)
1.383(4)
1.357(4)
1.3896
121.0(3)
120.7(3)
121.3(4)
120.9
119.8(3)
120.1(3)
120.2(4)
119.9
1
6
1.392(5)
1.392(5)
1.3894(15)
1.3903
119.0(4)
119.3(2)
119.9
Key:
Green = 1st ro structure
Blue = 2nd ro structure
Black = rs structure
Red = ab initio values
21
Comparison of pentafluorotoluene and
chloropentafluorobenzene
Pentafluorotoluene
Chloropentafluorobenzene
A (MHz)
1036.61221(15)
1028.5412(2)
B (MHz)
1030.94086(16)
751.82072(17)
C (MHz)
516.92066(11)
434.3531(3)
µ (Debye)
1.976(11)
0.415
<(C6-C1-C2)/°
115.5(3)
117.5(3)
Ia (u * Å2)
487.5295(7)
491.35520(11)
Ib (u * Å2)
490.21149(8)
672.20686(16)
Ic (u * Å2)
977.6723(2)
1163.5213(8)
Paa (u * Å2)
490.1772
672.1865
Pbb (u * Å2)
487.4952
491.3348
Pcc (u * Å2)
0.0343
0.0204
κ
0.9782
0.0686
Pcc = 1.566 u * Å2 for toluene (MP2/6-311++G(2d,2p))
Pcc = 1.554 u * Å2 for PFTOL (MP2/6-311++G(2d,2p))
22
Comparison of Chloropentafluorobenzene
to Chlorobenzene
Chloropentafluorobenzene
Chlorobenzene[7]
35Cl
37Cl
35Cl
37Cl
caa (MHz)
-79.521(11)
-62.68(2)
-71.25
-56.1
cbb (MHz)
43.598(4)
34.39(3)
36.88
29.03
ccc (MHz)
35.923(15)
28.29(6)
34.37
27.07
Paa (u * Å2)
672.1866
688.0581
320.5345
329.7352
Pbb (u * Å2)
491.3349
491.3342
89.1187
89.119
Pcc (u * Å2)
0.0209
0.0201
0.0453
0.0464
η* (MHz)
-0.0965
-0.0973
-0.0352
-0.0349
Q(35Cl)/Q(37Cl)
1.2698
1.2697
µ (Debye)
0.415
1.641
R(C1-Cl)/Å
1.716(5)
1.739
<(C6-C1-C2)/°
117.5(3)
121.7
*η = (Χbb – Χcc) / Χaa
23
[7] Oh, et. al. Structure of the chlorobenzene–argon dimer: Microwave spectrum
and ab initio analysis J. Chem. Phys. 113(22) 2000.
Conclusions
• Spectra of both molecules successfully assigned and
structures determined
• Internal rotation of pentafluorotoluene present, but not yet
characterized
• Dipole moments of the two molecules still either need to
be determined or still need to be completely understood
24
Acknowledgements
National Science Foundation
Williams Travel Award (EIU)
Justin Neill, Matt Muckle and Garry Grubbs
25
Toluene
experimental Pcc value:
0.029(10) u * Å2
1.5125 Å
119.0˚
1.394 Å
120.64°
120.17°
119.38°
Amir-Ebrahimi, V., Choplin, A. J. Mol.
Spec. 89 (1981), p. 42
1.395 Å
1.395 Å
26