Reduced dimensionality spin-orbit dynamics of CH3 + HCl $\rightleftharpoons$⇌ CH4 + Cl on ab initio surfaces

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 wavefunction 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 state dynamics are seen to play a small but significant role as consistent with experimental conclusions.

Benchmark ab initio and dynamical characterization of the stationary points of reactive atom + alkane and SN2 potential energy surfaces

“…26,28,109 Since then several groups have followed our ideas and developed SOcorrected PESs for reactions of halogen atoms with different molecules. 36,[110][111][112][113] In the 2010s the use of the explicitly-correlated CCSD(T)-F12 methods has become widespread for PES developments, 36,44,45,[114][115][116] which may diminish the significance of the traditional (non-F12-based) composite methods.…”

Accurate ab initio potential energy surface, thermochemistry, and dynamics of the Cl(2P, 2P3/2) + CH4 → HCl + CH3 and H + CH3Cl reactions

“…In 2007 Banks and Clary 25 developed a two-dimensional (2D) ab initio non-SO PES and very recently in 2011 they reported PESs for all the SO states, again in a 2D model. 26 The first full-dimensional ab initio PES was developed in…”

Empirical Valence Bond Theory Studies of the CH4 + Cl → CH3 + HCl Reaction

“…Reduced dimensionality quantum scattering studies were also carried out by Clary and coworkers in which the two spin-orbit states of the system were considered. [23][24]37 Treatment of all degrees of freedom of the reaction is feasible with classical scattering methods. For example, Troya and coworkers used a full-dimensional semi-empirical PES to perform quasi-classicaltrajectory (QCT) calculations.…”