Full-Dimensional Quantum Dynamics of the H + CH2D2 → H2 + CHD2 Reaction: Mode-Specific Chemistry in an Asymmetric Methane Isotopologue

Abstract

The hydrogen abstraction reaction H + CH₂D₂ → H₂ + CHD₂ serves as an essential benchmark for polyatomic reaction dynamics, yet its lack of C_3v symmetry has precluded full-dimensional quantum mechanical treatments. Here, we report the first full-dimensional (12D) time-dependent wave packet study of this reaction on an accurate potential energy surface. Our calculations reveal a striking hierarchy of mode-specific efficacy: excitation of the reacting CH₂ stretching modes enhances reactivity by factors of 8.7 and 7.6, while vibrational energy deposited into the spectator CD₂ modes proves less effective than translational energy. The torsional and rocking motions exhibit moderate promotional effects. At combustion-relevant temperatures, CH₂ stretching excitations collectively contribute over 53% of the thermal rate constant at 2000 K. This work establishes the first rigorous quantum mechanical baseline for mode-selective chemistry in an asymmetric methane isotopologue and provides a powerful framework for elucidating bond-specific dynamics in complex polyatomic systems.