Exploring the Moderate and High-resolution
Spectroscopy of Chemical Intermediates that can Affect
the Quality of Your Life
69th International Symposium on Molecular Spectroscopy
MA01
The Laser Spectroscopy Facility
Department of Chemistry
NO3
CH3CH2CH2O(T)
exp
ISMS Talks
MI12 and MI13
CH3O
Ag3
sim
29216.3
29217.3
29218.3
29219.3
29220.3
29221.3
29222.3
-1
Frequency (cm
)
C7H7
CH3CH2CH2O(G)
C5H5
exp
ISMS Talk TI04
sim
28632.0
28632.7
28633.3
28634.0
28634.7
28635.3
28636.0
28636.7
-1
F req uenc y (c m
)
C6F6+
ISMS Talk RJ08
and TJ14
Fraunhofer’s
Apparatus for
Observing the
Solar Spectrum
1814
C6H6+
Spectroscopy
Ohio
The Heart of It All
HC≡C-CH2O2
HOCH2CHO2
H2C=CH-CH2O2
NO3
CN
CH3C(O)O2
CH3O
CH3O2
OH
H2*
SO
SH
Radical Intermediates in Low Temperature Combustion
(Autoignition, Engine Knock)
Termination
Termination
·
RO2
NTC
Peroxy Radicals
·
RO
Alkoxy radical
M. J. Pilling, Comprehensive Chemical Kinetics, 35, 1(1997)
Day time
hν
RO2
OH
RH
O2
NO
hn
ROOH
HO2
RO2
NO
NO
NO2
HO2
O2
hn
RO
NO2
RO2NO2
NO2
NO
RONO2
RO
D
Isomerisation
Multistep
CO
OH O2
RO2  NO  RO  NO2
hn
NO2 
 NO  O
O2  O  O3
Night time
O3
PAN
R’CHO
hn O2
OH
NO
NO2
RO2
NO2
R’C(O)O2
NO3
NO2
RO
NO2
CO2
NO2  O3  NO3  O2
RO2  NO3  RO  NO2  O2
Lightfoot et. al. Atmos. Envir. 26A, 1805 (1992).
R. P. Wayne et al., Atmos. Envir. 25A, 1 (1991).
Day time
OH
RH
O2
OH
O2
hn
ROOH
HO2
RO2
NO
NO
NO2
HO2
O2
hn
NO2
RO2NO2
NO2
D
RONO2
Isomerisation
Multistep
CO
OH O2
R′=RH + OH → HOR′−R∙
HOR′−R∙ + O2 → HOR′−RO2
Night time
PAN
R’CHO
hn O2
HOR′–RO2
NO
RO
OH
NO
NO2
R’C(O)O2
R′=RH
NO3
O2
R′=RH
O2NOR′–RO2
NO2
CO2
Lightfoot et. al. Atmos. Envir. 26A, 1805 (1992).
R′=RH + NO3 → O2NOR′−R∙
O2NOR′−R∙ + O2 → O2NOR′−RO2
Key Chemical Intermediates in the Oxidation
of Organic Molecules in the Troposphere and
Low Temperature Combustion
Oxidizer Species
Hydroxyl Radicals, OH
Nitrate Radicals, NO3
Oxidized Products
Alkoxy Radicals, RO
Peroxy Radicals, RO2
Peroxy Radical (RO2) Electronic Structure
~2
X A//
O2
R
(2)
(4)
~2
~2
B A//
A A/
5.2 eV
0.9 eV
R
R
Spectroscopy of Alkyl Peroxies
CH3O2
~
b
~
~
a
~~ ~
B-X
A-X Transition
Transition
~
very
A
state
strong,
- bound
σ ~ 10-17 cm2/molecule
locatedvery
sharp,
in the
selective
UV, used in kinetics studies
~
B stateσ-~repulsive
weak,
10-20 cm2/molecule
broad, lack
requires
a tunable
of selectivity
light source in the NIR
a) Jafri et al., J. Am. Chem. Soc. 112, 2586 (1990).
b) O. J. Nielsen and T. J. Wallington, in Peroxyl Radicals, (John Wiley and Sons, New York, 1997).
Cavity Ringdown Spectroscopy (CRDS)
Experimental Setup
Initiation
650
O – 700 mJ
YAG 532 nm
75-115 mJ
Sirah Dye Laser
hn
R  X ( X  Br, I ) 
R  X
193nm
hn
R  C  R 
 R  R  CO
193nm
hn
 2Cl  2CO
COCl 2 
193nm
1.5 - 1.1 mm
Cl  RH  R  HCl
200-300 psi H2
Cell
 R  M ( N2 ) HRO
Production 2Ond2 Stokes
2 Raman
2  M ( N2 )
Filters
High Reflectivity Mirrors
1 – 3 mJ
Ringdown Cell
ArF
193 nm
Pulse Generator
100 – 200 mJ
PD
Cavity Ringdown Spectrum of CH3O2
800
origin
Absorption / ppm
600
COO bend
8 01
000
O-O stretch
701
400
811
1211
7011211
1222
200
8011211
7011222
0
7000
7500
8000
8500
Wave numbers / cm
-1
9000
~ ~
A-X Spectrum of C2H5O2
T conformer
300
B
250
A
Absorption /ppm
A
200
B
*
B
A
A
150
Origin
G conformer
OO stretch
COO bend
100
50
0
7000
*CH3O2
7200
7400
B
7600
7800
8000
Wave numbers /cm
8200
8400
8600
8800
-1
a) Rupper et al., J. Phys. Chem. A 111, 832 (2007).
Spectral/Structural Relationships
~~
A-X Origin Frequencies for Alkyl Peroxy Isomers (T1… conformers)
•
Branching or substitution at the α carbon
increases the transition energy
(~250-300 cm-1 from primary to secondary
isomers and ~150 cm-1 from secondary to
tertiary isomers)
•
Branching or substitution at the β carbon
decreases the transition energy
(~50-100 cm-1 from 1- isomers to iso-/neoisomers)
•
Increasing the number of carbons (n)
generally decreases the transition energy
(~20-30 cm-1 on average, up to 1-C3H7O2)
– frequency minimum of the straight
chain primary isomers observed at 1C3H7O2
– frequency minimum of the straight
chain secondary isomers observed at 2C4H9O2
Spectral/Structural Relationships
~~
A-X Origin Frequencies for Primary Alkyl Peroxy Conformers
•
A change in the OOCC dihedral angle
(i.e. giving a T1… or G1… conformer)
yields an average energy difference of
~100-200 cm-1 with the T1 conformers
lower in energy than the G1 for the
primary alkyl peroxies.
•
A change in the OCCC dihedral angle
offers an energy difference of ~50 cm-1
(see G1G2 conformer (7508 cm-1) vs.
G1′G2 conformer (7569 cm-1) for
C3H7O2 for example).
Benchmarking Calculations with
Experimental Results
Peroxy
isomer
Peroxy
Symmetry
conformer
Exp.
ROHF/
6-31+G(d)
B3LYP/
6-31+G(d)
G1/
6-31+G(d)
G2MP2a/
6-31G(d)
G2/
6-31+G(d)
TDDFT
Exp.- b/
6-31+G(d)
Theor.
CIc
double ς
EOMIPCCSD/DZP
7372
7375
8
9655
7267
7901
7355
7
7938d
7580
12
8059d
methyl
T
Cs
7383
4321
7513
7257
ethyl
T
Cs
7362
4332
7505
7247
ethyl
G
C1
7592
4519
7659
7473
1-propyl
T1T2
Cs
7332
4313
7460
7221
7317
15
7920e
1-propyl
T1G2
C1
7332
4312
7455f
7204f
7317f
15
7932e
1-propyl
G1G2
C1
7508
4446
7567f
7364f
7477f
31
7970e
1-propyl
G1T2
C1
7569
4523
7649f
7465f
7567f
2
8091e
1-propyl
G1′G2
C1
7569
4610
7645f
7555f
7643f
-74
8143e
2-propyl
G
C1
7567
4524
7649
7467
7566
1
8224e
2-propyl
T
Cs
7701
4625
7756
7684
7771
-70
1-butyl
T1T2T3
Cs
7355
4314
7463
7225
7321
34
isobutyl
T1T2
Cs
7306
4302
7426
7188
7288
18
1-pentyl
T1T2T3T4
Cs
7351
4312
7459
7224
7321
30
neopentyl
T1T2
Cs
7267
4289
7392
7164
7252
15
3-pentyl
T1T2T3
Cs
7643
4434
7551
7445
7532
111
a
7590
7566
M. S. Stark, J. Am. Chem. Soc. 122, 4162 (2000). b Vertical excitation, J. L. Weisman and M. Head-Gordon, J. Am. Chem. Soc. 123, 11686 (2001). c J. A. Jafri and D. H. Phillips, J. Am.
Chem. Soc. 112, 2586 (1990). d P. Rupper, E. N. Sharp, G. Tarczay, and T. A. Miller, J. Phys. Chem. A 111, 832 (2007), publication 3. e G. Tarczay, S. J. Zalyubovsky, and T. A. Miller,
Chem. Phys. Lett. 406, 81 (2005). f G. M. P. Just, P. Rupper, and T. A. Miller, to be published.
Peroxy Radical Spectra from Octane Components of Gasoline
000
70
O-O
stretch
sec-isomer
n-octane
60
H3C-(CH2)6-CH3
ppm/pass
000
0 00
Iso-octane
50
tert
40
tert
30
20
7200
7400
7600
7800
O-O
stretch
C-O-O
bend
pri
8000
8200
tert
pri
8400
8600
-1
Wavenumber (cm )
8800
9000
9200
HR-JC-CRDS Experimental Setup
20 Hz, 8ns, 350 mJ
Nd:YAG pulsed laser
730 - 930 nm, Dn ~ 1 MHz
Nd:YVO4
cw laser
Ti:Sa ring
cw laser
50 - 100 mJ
Dn ~ 8 - 30 MHz (FT limited)
SRS (1 m, 13 atm H2, Δν~200 MHz)
Ti:Sa
Amplifier
(2 crystals)
Raman Cell
BBO
DFM (Δν~50 MHz)
Ring-down cavity with slit-jet discharge
(absorption length ℓ = 5 cm)
L = 67 cm
Nd:YAG pulsed laser
(seeded)
20 Hz, 8ns, 500 mJ
PD
InGaAs
Detector
ℓ
1-5 mj, <100MHz
R ~ 99.995 – 99.999% @ 1.3 mm
Vacuum Pump
CRDS Spectroscopy of CD3O2 at RT
600
600
absorption / ppm
500
400
400
300
300
200
200
100
100
0
7000
7000
7200
7400
7400
7600
7600
cm/-1cm-1
wave numbers
7800
7800
8000
8000
Jet-cooled CRDS Spectrum of CD3O2
~
A 2A’ ←
~
X 2A”, vibrationless band 000
p1 Q
r0 Q
• Cs symmetry → pure c-type
transition moment
• close to a prolate symmetric
top (ΔKK” ΔJ)
• spread out over ~ 30 cm-1
• > 1000 lines, 350 of which
due to single transition
• 10 % O2 and ~ 1% CD3I in Ne
• dc discharge: 350 mA
• stepsize: 50 MHz
• RD time average: 4
Jet-Cooled Spectra of CD3OO
(P and R branch)
– experiment
– simulation (14K)
Absorption per pass (ppm)
4
2
0
7367
7368
7369
7370
7371
7372
6
4
2
0
7377
7378
7379
Wavenumber (cm-1)
7380
7381
CD3O2 Molecular Parameters
Parameters
Exp
(in cm-1)
G2-Exp
(in %)
DFT-Exp
(in %)
A”
1.29323 (10)
0.087 (8)
0.680 (8)
B”
0.32079 (11)
0.70 (3)
-1.23 (3)
C”
0.28546 (11)
0.57 (4)
-0.95 (4)
εaa”
-0.0718 (15)
-
-
εbb”
-0.0091 (14)
-
-
εcc”
-0.0003 (15)
-
-
½(εab+εba)”
0.0138 (22)
-
-
A’
1.17813 (10)
-0.123 (8)
2.738 (8)
B’
0.32707 (11)
0.40 (3)
-2.62 (3)
C’
0.28387 (11)
0.38 (4)
-1.51 (4)
εaa’
0.0695 (15)
-
-
εbb’
0.0107 (14)
-
-
εcc’
-0.0029 (15)
-
-
½(εab+εba)’
0.0218 (22)
-
-
Jet-cooled CRDS Spectra of the Origin Bands of
C2D5O2 and C2H5O2
TR∼ 15K
TR∼ 70K
Hydroxy Alkyl Peroxy Radicals
Hydroxyl Ethyl Peroxy (β-HEP)
• Hydroxy peroxy radicals are produced from OH mediated
oxidation of ethene and other alkenes
• Key intermediate in oxidation of ethanol and other bio-fuels
Ethene Emission sources
26% Human made
74% Natural sources
Total emission: 18-45 X 106 T/yr
140
World Ethanol production
120
Ethene sink processes
Billion Liters
100
89% OH
80
60
40
20
8% O3
β-Hydroxyethyl peroxy (β-HEP)
0
2006
2008
2010
2012
2014
2016
2018
Year
3% to the Stratosphere
S. Sawada and T. Totsuka, Atmos. Environ. 20, 821 (1986)
FAPRI 2008 U.S. and World Agricultural Outlook
Ö X̃ Spectrum of Hydroxyl
Ethyl Peroxy (β-HEP)
80
Absorbance (ppm/pass)
HO2
60
CH3O2
40
I atom
Ethene precursor
Iodoethanol precursor
20
7200
7400
7600
7800
8000
8200
wavenumber (cm-1)
8400
8600
8800
à State Vibrational Assignments
60
00
0
Exp.
G1G2G3 sequence + franck condon factor + rotational simulations
G1'G2G3 sequence + franck condon factor + rotational simulations
Absorbance (ppm/pass)
50
15012001(16012001)
G1G2G3
40
2101
I atom
30
0 00
1
1
15012101(16012101)
150 (160 )
2001
1501(1601)
2
200 / 210
2
20
G1’G2G3
10
0
7200
7400
7600
7800
8000
8200
8400
-1
wavenumber (cm )
-Frank condon factor calculated from molfc 2.3.4
-Vibrational frequencies [UB3LYP/aug-cc-pVTZ]
8600
8800
Normal
Modes
Description
21
20
16
15
16
15
COO bending
CCOH torsion
O-O stretch
O-O stretch
O-O stretch
O-O stretch
A state (cm-1)
Calc.
344
421
922
970
930
967
Exp.
345
387
911
911
904
904
Jet-cooled experimental data
4
Specview simulation (asymmetric top)
with Δν=150MHz, rotational constants
are from MP2(Full)/6-31G* optimized
geometry.
ppm/pass
3
2
1
0
-1
7380
7385
7390
excitation energy / cm
7395
-1
7400
Upper = exp. data
Lower = simulation from EA analysis
Isotope shifts observed among four
different isotopologues.
Rotational constants and Lorentzian
linewidth (ΔνL) are obtained for each
isotopologue by evolutionary
algorithm.
7386
7388
7390
7392
excitation energy / cm
7394
-1
7396
W. L. Meerts, M. Schmitt, Int. Rev. Phys. Chem. 25, 353 (2006)
G. M. P. Just, P. Rupper, T. A. Miller and W. L. Meerts J. Chem. Phys., 131, 184303 (2009)
G. M. P. Just, P. Rupper, T. A. Miller and W. L. Meerts Phys. Chem. Chem. Phys., 12, 4773 (2010)
Natural linewidth (ΔνL)
Dn L 
1
2
ΔνL~7200 MHz
ΔνL~8300 MHz
ΔνL~3500 MHz
ΔνL~2500 MHz
τβ-HEP~22 ps
τβ-HEP-d4~19 ps
τβ-DHEP~45 ps
τβ-DHEP-d4~64 ps
16000
a)
Transition state energies are ZPE corrected.
b)
BB1K/6-31+G(d,p), K. T. Kuwata et al., J. Phys. Chem. A, 111, 5032 (2007)
c)
RCCSD(T)/6-311+G(3df,2p), S. Olivella and A. Solé, J. Phys. Chem. 108, 11651 (2004)
14000
d)
MRCI/cc-pVQZ, J. Zádor et al., Proc. Combustion Inst. 32, 271 (2009)
e)
B3LYP/6-311++G(d,p), present work.
f)
SAC-CI/6-31+G**, present work.
12000
-1
Experimental determined band origin in the present work.
relative energy / cm
g)
e), f)
b), c), d), e), f)
10000
8000
b), c), d)
6000
4000
2000
0
rxn. coordinate
rxn. coordinate
16000
a)
Transition state energies are ZPE corrected.
b)
BB1K/6-31+G(d,p), K. T. Kuwata et al., J. Phys. Chem. A, 111, 5032 (2007)
c)
RCCSD(T)/6-311+G(3df,2p), S. Olivella and A. Solé, J. Phys. Chem. 108, 11651 (2004)
14000
d)
MRCI/cc-pVQZ, J. Zádor et al., Proc. Combustion Inst. 32, 271 (2009)
e)
B3LYP/6-311++G(d,p), present work.
f)
SAC-CI/6-31+G**, present work.
12000
-1
Experimental determined band origin in the present work.
relative energy / cm
g)
10000
7389.09 cm-1 g)
8000
τβ-HEP~20 ps
I.C.
6000
4000
2000
0
rxn. coordinate
rxn. coordinate
Importance and History of Criegee Intermediates
• First proposed by Rudolf
Criegee in 1949 as
intermediate in
ozonylsis of alkenes.
• Formed in the
atmosphere and utilized
heavily in organic
chemistry to
functionalize double
bonds
a. Criegee, R. and Wenner, G. Chem. Ber., 1949, 9, 564.
c. Criegee, R. Agnew. Chem., Int. Ed. Engl. 1975, 14, 745
b. Smith, M. B. and March, J. March‘s Advanced Organic Chemistry: Reactions
and Mechanisms, and Structure, 6th ed. John Wiley & Sons, Inc. 2007.
Recent Literature on Criegee Intermediates
2012, 335, 204.
2013, 340, 174.
Electronic Structure of Methylene Peroxy and Ozone
C=1s22s22p2
O=1s22s22p4
1A’
3A’
1A
1
3A
2
3A
2
3A’
9530 cm-1
1A’
1A
1
1. Harding, L. B. and Goddard III, W. A. J. Am. Chem. Soc. 1978, 100, 7180-7188.
2. Wadt, W. R. and Goddard III, W. A. J. Am. Chem. Soc. 1975, 97, 3004-3021.
Production of Criegee Intermediate
• Huang, H.; Eskola, A.; Taatjes, C. A. J. Phys. Chem. Lett. 2012, 3, 3399.
Experimental Spectrum
875 cm-1, Typical OO Stretch Frequency
20
Iodine atom
2P  2P
1/2
3/2
+
Absorbance (ppm/pass)
+
15
H2O
Contamination
+
+
+
+
10
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
5
Precursor
Absorption
+
Precursor
Absorption
0
7000
7500
8000
Wavenumber (cm-1)
8500
9000
Assigning Carrier of the Spectrum
There are two likely carriers that can be responsible for the spectrum:
•
•
•
•
•
Photolysis of CH2I2 with O2 is the standard method used to produce the Criegee intermediate
We observe the spectrum under conditions of ~0.1 torr CH2I2 in ~90 torr total pressure of
O2/N2 with O2 up to 90%, as reported by Y.P. Lee group1
Mechanism requires libration of I upon reaction of CH2I+O2. Photolysis of CH2I2 with O2
present shows a nearly 50% increase in I atom signal compared to the photolysis without O 2
Consistent with results of the Lee group, we have measured a very rapid self-reaction decay
rate of order k=4x10-10 cm3 molecule-1 s-1. By comparison for methyl peroxy k=5x10-13 cm3
molecule-1 s-1
SO2 is an effective scavenger for our spectral carrier and CH2O2 has a reported rate constant
of k=4x10-11 cm3 molecule-1 s-1 while peroxy radicals react slowly, e.g. for CH3O2 k≤1x10-16
cm3 molecule-1 s-1
1. Su, Y.; Huang, Y.; Witek, H. A. and Lee, Y. P. Science 2013, 340, 174.
Comparison of Spectra
Absorbance (ppm/pass)
30
20
10
0
7000
7500
CH2ClO2 (CH2ClI, CH2Cl2) Shifted + 15 ppm
CH2BrO2 (CH2Br2, CH2BrI) Shifted +7 ppm
???? (CH2I2)
8000
8500
Wavenumber
9000
Conclusions
• Ambient Temperature and Jet-cooled Moderate Resolution, and
High Resolution, Rotationally Resolved, NIR CRDS have
Characterized the Spectroscopy, Electronic and Geometric Structure
of the Alkyl Peroxy (RO2) Radicals
• For Alkyl Peroxy
Radicals Experimental Spectral/Structural Relationships
have been Developed to Identify their Chemical Formula, as well as Isomeric
and Conformeric Structure. An Extensive Set of Spectroscopic Data is
Available to Benchmark Electronic Structure Calculations
• Spectroscopic Studies of
Hydroxy Alkyl Peroxy Radicals Reveal
Dynamical Effects in the à State of β-HEP which are Consistent with
Isomerization Between (HORO2) and ·ORO2H
• A Similar NIR CRDS Spectrum Has Been Observed That May be
Attributable to the Criegee Intermediate, Methylene Peroxy, CH2O2.
Chemical Evidence Appears Consistent With That Result, but Definitive
Spectral Evidence and Confirming Theoretical Computations Are Not Yet
Available
ACKNOWLEDGEMENTS
Graduate Students
Undergraduate Student
Terrance Codd - OSU
Henry Tran
Post-docs
Neal Kline - OSU
Mourad Roudjane -OSU
Meng Huang- OSU
Jinjun Liu –
Faculty, U. Louisville
Ming-Wei Chen –
Post-doc U. Illinois
Rabi Chhantyal Pun –
Post-doc U. Bristol, UK
Gabriel Just –
Post-doc U.C. Berkeley
Staff –Agilent Research
U. S. Department of Energy
Research Scientist
Dmitry Melnik - OSU
$$$$$$