Understanding Rotational Mode Speci city in the O(³P)+CHD₃→OH+CD₃ Reaction by Simple Reactant Alignment Pictures

The mode specificity plays an important role in understanding the fundamental reaction dynamics. This work reports a theoretical study of the rotational mode specificityof the reactant CHD₃(JK) in the prototypical hydrocarbon oxidation reaction O(³P)+CHD₃→OH+CD₃. The time-dependent quantum wave packet method combined with a seven-dimensional reduced model is employed to calculate the reaction probability on an accurate potential energy surface. The obtained reaction probability depends on the values of both K and Ktot with P_Ktot=K=0>P_Ktot=K=J>P_Ktot=J,K=0=P_Ktot=0,K=J. This observation can be well rationalized by the reactant alignment pictures. Rotational excitations of CHD₃ up to the angular momentum quantum number J=4 have a very weak enhancement effect on the reaction except for the state (J=4, K=0). In addition, the rotationally excited states of CHD₃ with K=0 promote the reaction more than those with K=J. The quantum dynamics calculations indicate that the K=0 enhancements are mainly caused by the contributions from the components with K=K_tot=0. The components correspond to the tumbling rotation of CHD₃, which enlarges the range of the reactive initial attack angles.