1. Torsion-Vibration Couplings in the Methyl Peroxy Radicals
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Torsion-Vibration Couplings in the Methyl Peroxy Radicals
Meng Huang, and Terry A. Miller
Department of Chemistry and Biochemistry
The Ohio State University
Anne B. McCoy
Department of Chemistry
University of Washington
Kuo-Hsiang Hsu, Yu-Hsuan Huang, Yuan-Pern Lee
Applied Chemistry
National Chiao Tung University
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

2. Introduction CH3OO Radical
1/11/ :38 AM
Introduction CH3OO Radical
In combustion and atmospheric chemistry, alkyl peroxy radicals are important intermediates
Oxidation of NO to form NO2 (Formation of Ozone)
Formation of acid rain
Reaction intermediate of fossil fuels combustion
Methyl peroxy is the simplest alkyl peroxy radical
The methyl group torsion in methyl peroxy provides good system for studying the effect of large amplitude motion
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

3. CH3OO· IR Spectrum 𝑣2 𝑣9 Experimental Results (cm-1) Harmonic Values
Fourier Transform Infrared Spectrum of CH3OO Radical in Mid-IR Range from Yuan-Pern Lee’s Group (T ~ 300K, Resolution ~ 0.17 cm-1) 𝑣2 𝑣9
Experimental Results
(cm-1)
Harmonic Values 𝑣2
2954.3
3074.5 𝑣9
3021.4
3169.1 𝑣1
3032.3
3181.3
𝑣tor --
140.3 𝑣1
Tv = 300K,
Barrier Height of torsion: cm-1
B3LYP/aug-cc-pVTZ 𝑣2 𝑣9 𝑣1

4. Simulation of the 𝑣2 fundamental band without torsional hot bands
Precursor
Absorption
TR = 300K; νtor = cm-1
B3LYP/aug-cc-pVTZ

5. Simulation of the 𝑣9 and 𝑣1 fundamental bands without torsional hot bands
TR = 300K; νtor = cm-1
B3LYP/aug-cc-pVTZ

6. Four dimensional model

7. The torsional rotational coupling
The methyl torsion would generate an internal angular momentum which contributes to the rotation of the entire molecule.
From principle axis system to rho-axis system
G. M. P. Just, A. B. McCoy, T. A. Miller J. Chem. Phys. 127, (2007)
J. T. Hougen, I. Kleiner, M.Godefroid J. Mol. Spectrosc. 1994, 163, 559.

8. The tunneling splittingtE tA
With the above eigenvalues we can simulate the rotational structure with parameters from tunneling splitting calculated by vibrational torsional model.
J. T. Hougen, I. Kleiner, M.Godefroid J. Mol. Spectrosc. 1994, 163, 559.

9. The simulation of the rotational contour of ν2 band with the torsional sequence bands
K.-H. Hsu, Y.-H. Huang, Y.-P. Lee, M. Huang, T. A. Miller, and A. B. McCoy, J. Phys. Chem. A, DOI: /acs.jpca.5b12334

10. The simulation of the rotational contour of ν2 band with the torsional sequence bands

11. Accidental degeneracy between ν2+νtor and ν9/ν1
Hunc
ν9=1 νt=1
Hunc+Hcpl
ν2=1 νt=1
ν2=1 νt=1
ν1=1 νt=0
ν9/ν1=1 νt=0
ν9=1 νt=0
Can we understand the effect of this accidental degeneracy on ν9 and ν1 ?
ν2=1 νt=0
ν2=1 νt=0
νt=1
νt=1
νt=0
νt=0

12. The effect of the vibrational-torsional coupling on the degenerate CH stretches ν1 and ν9
vE,vE
vE,vE
vE,tA
vE,tA
J. T. Hougen, J. Mol. Spectrosc. 207, 60, (2001)

13. The effect of the vibrational-torsional coupling on the degenerate CH stretches ν1/ν9
vtA
vE,vE
vE,vE
vtE
vtA
vE,tA
vE,tA
vtE

14. Torsional quantum number
The vibration-torsion energy pattern on the degenerate CH stretch states A1
A1+ A2+E
A1+E E
Eunc
Eunc
Eunc A2
A2+E E E
Torsional quantum number
CH3OO Eigenstates
νt = 0
(cm-1)
νt = 2
νt = 4
νt = 6
ν1(vtA1)
ν1(vtE)
ν9(vtA2)
ν9(vtE)
X. Wang, D.S. Perry J. Chem. Phys., 109, (1998)
J. T. Hougen, J. Mol. Spectrosc. 207, 60, (2001)
D.S. Perry, J. Mol. Spectrosc. 257, 1, (2009)
L.-H. Xu, J. T. Hougen, R. M. Lees J. Mol. Spectrosc. 293–294, 38, (2013)
B. P. Thapaliya, M. B. Dawadi, C. Ziegler, D. S. Perry, Chem. Phys. 480, 31(2015)

15. Effect of accidental degeneracy between ν2+νtor and ν9 on torsional splittings
vtA
vtA
ν2+νtor(A’’)
ν2+νtor(A’’)
vtE
vtE
vtA
vtA
ν1(A’)
ν1(A’)
vtE
vtE
vtA
vtA
ν9(A’’)
ν9(A’’)
vtE
vtE

16. The correlation between the simulation constants for ν2 and ν9/ν1 bands

17. The simulation of the rotational contour around ν9/ν1 fundamentals with the torsional sequence bands

18. The simulation of the rotational contour around ν9/ν1 fundamentals with the torsional sequence bands

19. Summary
A reduced dimensional model including CH stretches and torsion is used to calculate the torsional sequence band structure on ν2, ν9 and ν1 band of CH3OO radical.
The rotational structure of the spectra around ν2 and ν9 /ν1 fundamental bands region are simulated with the same model considering the torsional sequence band structure and torsional rotational coupling.
The parameters used in both simulations are consistent with the fact that there are accidental degeneracies of the ν2 + nvtor with respect to ν9 + (n-1) vtor which shifts the sequence bands around.
There are qualitative agreements between experiment and simulations in both ν2 and ν9 /ν1 regions.

20. Dr. Terry A. Miller
Henry K. Tran
Scott M. Garner
Dr. Anne B. McCoy
Bernice Opoku-Agyeman
Laura C. Dzugan
Dr. Lindsey R. Madison
Kyle H. McGrath
Victor G. M. Lee
Dr. Yuan-Pern Lee
Kuo-Hsiang Hsu
Dr. Yu-Hsuan Huang

21. Effect of accidental degeneracy between ν2+νtor and ν9 on torsional splittings
vtA
vtA
A’’
A’’
vtE
vtE
vtA
vtA A’ A’
vtE
vtE
vtA
A’’
vtA
vtE
A’’
vtE

22. The correlation between the simulation constants for ν2 and ν9/ν1 bands