Vibrational Mode-Specific Dynamics of the OH + C₂H₆ Reaction

We investigate the effects of the initial vibrational excitations on the dynamics of the OH + C₂H₆ → H₂O + C₂H₅ reaction using the quasi-classical trajectory method and a full-dimensional analytical ab initio potential energy surface. Excitation of the initial CH, CC, and OH stretching modes enhances, slightly inhibits, and does not affect the reactivity, respectively. Translational energy activates the early-barrier title reaction more efficiently than OH and CC stretching excitations, in accord with the Polanyi rules whereas CH stretching modes have similar or higher efficacy than translation, showing that these rules are not always valid in polyatomic processes. Scattering angle, initial attack angle, and product translational energy distributions show the dominance of direct stripping with increasing collision energy, side-on OH and isotropic C₂H₆ attack preferences, and substantial reactant-product translational energy transfer without any significant mode specificity. The reactant vibrational excitation energy of OH and C₂H₆ flows into the H₂O and C₂H₅ product vibrations, respectively, whereas product rotations are not affected. The computed mode-specific H₂O vibrational distributions show that initial OH excitation appears in the asymmetric stretching vibration of the H₂O product and allow comparison with experiments.