Ro-Vibrational Mode Specificity in the Dynamics of the OH + CH ₃ OH Reaction

We report a mode-specific quasi-classical trajectory investigation of the prototypical multichannel reaction OH + CH₃OH on a full-dimensional fundamental invariant neural-network potential energy surface, supplemented by sudden-vector-projection analysis. By selectively exciting individual ro-vibrational modes of CH₃OH and OH and varying the collision energy, we systematically examined the two H-abstraction channels over a broad energy range. In the CH₂OH channel, excitation of the C-H stretch provides the most pronounced enhancement across all collision energies, while OH rotational excitation becomes comparably effective at high energies. In contrast, the O-H stretch and CH₃ torsion exert more modest, energy-dependent effects. In the CH₃O channel, the methanol O-H stretch dominates the promotion of reactivity, whereas the C-H stretch and torsion contribute primarily at low energies, and the OH rotation has a weak inhibitory effect at high energies. Both channels display a transition from complex-mediated to direct abstraction mechanisms with increasing collision energy, as reflected in angular-scattering patterns and product energy distributions. These results provide detailed insight into how distinct ro-vibrational excitation control pathways affect selectivity and dynamical behavior in polyatomic hydrogen-abstraction reactions.