Mode specificity of a multi-channel reaction prototype: F + CH3OH → HF + CH3O/CH2OH

Abstract

Mode-specific chemistry has been a hot research topic in the field of molecular reaction dynamics since different degrees of freedom play potentially divergent effects on the reactivity of different channels and the associated product branching ratios. In this work, we examine the mode specificity effect in the reaction F + CH3OH → HF + CH3O (R1)/CH2OH (R2), a prototypical polyatomic reaction with multiple channels and submerged barriers, by extensive vibrational state-specific molecular dynamical calculations with the quasi-classical trajectory approach on a globally accurate full-dimensional potential energy surface. Complicated mode specificity effects are revealed. In particular, the vibrational excitations of the O–H stretching motion and the torsional motion with respect to the C–O axis can enhance the reactivity of R1 significantly. The excitations of the C–H stretching vibrational motions do not influence R1. For another channel, R2, the C–H stretching vibrational excitation shows some weak enhancement effect, while the O–H stretching vibrational excitation shows no effect on the reactivity. Then, the sudden vector projection model is employed to rationalize the mode specificity effects and understand the product energy partitioning in the two channels. The ro-vibrational state distributions of the nascent product HF/DF from F + CH3OH/CH3OD/CD3OH/CD3OD are also in good agreement with available experiments.