Quantum Dynamics Study of the F + CH4 → HF + CH3 Reaction on an Ab Initio Potential Energy Surface

Abstract

A quantum reactive dynamics, four degree-of-freedom, time-dependent wavepacket method is applied to study the F + CH4 → HF + CH3 reaction using a slightly modified version of the ab initio potential energy surface of Czakó et al. [ J. Chem. Phys. 2009 , 130 , 084301 ]. A common resonance peak is found on all initial state-selected reaction probabilities close to the reaction threshold. The resonance also survives the averaging of partial waves and shows up in the integral cross section just after the threshold energy, in agreement with experiment. This early- barrier polyatomic reaction is more enhanced by the translational motion than the vibrational motion for energies below 0.38 eV; however, the reverse is true for energies higher than 0.38 eV. The vibrational excitation of the CH stretching mode enhances the reactivity, whereas the excitation of the umbrella mode of CH4 hinders the reactivity. The calculated thermal rate constants are in good agreement with one direct experimental measurement.