Comparative study of the H and D abstraction in the H + CH₃D reaction with a ten-dimensional quantum dynamics model

The mode selectivity in the prototypical H + CH₃D reaction is investigated by the initial state selected time-dependent wave packet method within a ten-dimensional quantum dynamics model. The model is a novel reduced dimensional model for the X + YCZ₃ reaction, which allows the CZ₃ to break C_3V symmetry. The calculated reaction probabilities initially from different reactant vibrational states show that the CH₃ stretching modes excitations obviously promote the H-abstraction reaction but have a slight influence on the D-abstraction reaction. In contrast, the CD stretching mode excitation significantly enhances the D-abstraction reaction. For both H- and D-abstraction reactions, the excitation of either the CH₃ umbrella bending mode or the CH₃ rocking mode shows a promotional effect on the reactivity, while fundamental excitation of the CH₃ bending mode has a negligible effect. Impressively, the first-overtone excitation of CH₃ bending mode remarkably promotes the H-abstraction reaction, resulting from the 1:2 Fermi coupling between the CH₃ symmetric stretching mode and the first overtone of CH₃ bending mode. In addition, translational energy is more efficient than vibrational energy in promoting the H-abstraction reaction at low energy, while vibrational energy becomes more efficient for the D-abstraction reaction.