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

The hydrogen abstraction reaction H + CH2D2 → H2 + CHD2 serves as an essential benchmark for polyatomic reaction dynamics, yet its lack of C3v 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.