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Reduced dimensionality spin-orbit dynamics of CH_{3} + HCl CH_{4} + Cl on *ab initio* surfaces

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10.1063/1.3592732

### Abstract

A reduced dimensionality quantum scattering method is extended to the study of spin-orbit nonadiabatic transitions in the CH_{3} + HCl CH_{4} + Cl(^{2}P_{J}) reaction. Three two-dimensional potential energy surfaces are developed by fitting a 29 parameter double-Morse function to CCSD(T)/IB//MP2/cc-pV(T+d)Z-dk *ab initio* data; interaction between surfaces is described by geometry-dependent spin-orbit coupling functions fit to MCSCF/cc-pV(T+d)Z-dk *ab initio* data. Spectator modes are treated adiabatically via inclusion of curvilinear projected frequencies. The total scattering wave function is expanded in a vibronic basis set and close-coupled equations are solved via R-matrix propagation. Ground state thermal rate constants for forward and reverse reactions agree well with experiment. Multi-surface reaction probabilities, integral cross sections, and initial-state selected branching ratios all highlight the importance of vibrational energy in mediating nonadiabatic transition. Electronically excited statedynamics are seen to play a small but significant role as consistent with experimental conclusions.

© 2011 American Institute of Physics

Received 01 March 2011
Accepted 02 May 2011
Published online 26 May 2011

Acknowledgments: This work was supported by the Engineering and Physical Sciences Research Council (Grant No. EP/G00224X/1) and the United States Office for Naval Research (ONR) (Grant No. N00014-05-1-0460). S.M.R. acknowledges the Oxford University Press for receipt of a Clarendon Scholarship. Calculations were run in part using the Oxford Supercomputing Centre resources. We would like to thank Dr. Frank von Horsten, Dr. Ivan Ljubić, Dr. Stuart Greaves, Dr. Rebecca Rose, Professor Joel Bowman, and Professor Kopin Liu for useful discussions.

Article outline:

I. INTRODUCTION

II. BACKGROUND THEORY

A. Approximate diabatic representation

B. Multi-surface reaction model

C. Hyperspherical coordinates

III. SYSTEM ENERGETICS

A. Basis set tests

B. Stationary points

C. Grid development and frequency projection

D. Potential energy surfaces

1. Diabatic surfaces

2. Spin-orbit coupling potentials

3. Surface characterisation

IV. SCATTERING THEORY

A. Scattering equations and R-matrix propagation

B. Dynamics

C. Kinetics

D. Numerical details

V. SINGLE-SURFACE SCATTERING RESULTS

VI. MULTI-SURFACE SCATTERING RESULTS

A. Hyperspherical adiabats

B. Geometry of nonadiabatic transitions

C. CH_{3} + HCl → CH_{4} + Cl(^{2}P)

1. Reaction probabilities

2. Integral cross sections

3. Nonadiabatic branching ratio.

D. Cl (^{2}P_{J}) + CH_{4} → HCl + CH_{3}

E. Nonreactive scattering

VII. CONCLUSIONS

/content/aip/journal/jcp/134/20/10.1063/1.3592732

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2011-05-26

2014-04-23

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