TorsionVibration Couplings in the Methyl Peroxy Radicals CH

Torsion-Vibration Couplings in the Methyl Peroxy Radicals CH 2 XOO Systems (X = Cl, Br, I) FD 05/06 9: 38 AM Meng Huang, Anne B. Mc. Coy and Terry A. Miller Department of Chemistry and Biochemistry The Ohio State University

Introduction CH 3 OO Radical In combustion and atmospheric chemistry, alkyl peroxy radicals are important intermediates Oxidation of NO to NO 2 (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

CH 3 OO· IR Spectrum Fourier Transform Infrared Spectrum of CH 3 OO Radical in Mid-IR Range from Yuan-Pern Lee’s Group (T ~ 300 K, Resolution ~ 0. 15 cm-1) Experimental Results (cm-1) Harmonic Values (cm-1) 2954. 3 3074. 5 3021. 4 3169. 1 3032. 3 3181. 3 -- 140. 3 Fourier Transform Infrared Spectroscopy of CH 3 OO Radical in Mid-Infrared Range Kuo-Hsiang Hsu and Yuan-Pern Lee Meng Huang and Terry A. Miller MSS, 2013

Simulation of the �� 2 Band with the �� 2 Fundamental Transition Precursor Absorption Parameters (cm-1) A’’ 1. 730 B’’ 0. 379 C’’ 0. 330 A’ 1. 726 B’ 0. 379 C’ 0. 330 a: b: c 0. 91: 0. 09: 0 TR = 300 K; νtor = 140. 3 cm-1 B 3 LYP/aug-cc-p. VTZ Frequency(cm-1)

Torsional Sequence Bands Frequency(cm-1)

Coupled Anharmonic Oscillators Frequency(cm-1)

Possible Torsional Band Structure to Simulate the Spectrum Frequency(cm-1)

Sim Exp G. M. P. Just, A. B. Mc. Coy, T. A. Miller J. Chem. Phys. 127, 044310 (2007)

Model for Simulation of Torsional Sequence Band G. M. P. Just, A. B. Mc. Coy, T. A. Miller J. Chem. Phys. 127, 044310 (2007) J. T. Hougen, I. Kleiner, M. Godefroid J. Mol. Spectrosc. 1994, 163, 559.

Model for Simulation of Torsional Sequence Band

Hamiltonian: Torsional Levels on CH Stretch

The Calculated Vibrational Structure Ab initio calculation at the B 3 LYP/aug-cc-p. VTZ level of theory Frequency(cm-1)

The Uncoupled Hamiltonian Ab initio calculation at the B 3 LYP/aug-cc-p. VTZ level of theory

The Effect of Coupling Ab initio calculation at the B 3 LYP/aug-cc-p. VTZ level of theory

The Effect of the Coupling on the CH Stretch Ground State No significant effects on the ground state

The Effect of Coupling Ab initio calculation at the B 3 LYP/aug-cc-p. VTZ level of theory

The Effect of Coupling on the �� 2 Excited State Strong coupling between v 2 + nvtor and v 9 /v 1 + (n-1) vtor

Energy Diagram

Energy Diagram – The First Torsional Sequence Band Uncoupled Eigenvalues Blue shift Eigenvalues with Couplings

Possible Torsional Band Structure to Simulate the Spectrum Experiment al Results (cm-1) 2954. 3 3021. 4 The first torsional band has to be shifted to the blue. 67. 1 cm-1 3032. 3 ? Frequency(cm-1)

Energy Diagram

Energy Diagram – The First Torsional Sequence Band Uncoupled Eigenvalues Blue shift Red shift Eigenvalues with Couplings Increase in tunneling splitting!

The simulation of the rotational contour with the torsional sequence bands Frequency(cm-1)

Summary A reduced dimensional model including CH stretches and CH 3 torsion is used to calculate the torsional sequence band structure on ν 2 band of CH 3 OO radical. The structure depends on the accidental degeneracies of the ν 2 + nvtor with respect to ν 9/ν 1 + (n-1) vtor. The increasing of the tunneling splittings for the sequence bands, which are the result from the coupling, could lead to possible broadening effect of the Q-branch of rotational structure. Under the current model, it is still hard to simulate the entire rotational contour of the ν 2 band. However, couplings from other degrees of freedom such as Fermi resonance may also contribute to the broadening effect. Mode Freq Difference(cm-1) Cubic Coupling Constants(cm-1) ν 2 /2ν 4 83. 390 129. 475 ν 2 /2ν 5 165. 644 215. 906

Dr. Terry A. Miller Henry Tran Dr. Anne B. Mc. Coy Zhou Lin Bernice Opoku-Agyeman Laura C. Dzugan Melanie L. Marlett Jason F. Ford Scott M. Garner Dr. Y. P. Lee