State-to-state dynamics study on the C(¹D) + HD (v = 1, j = 2) Insertion Reaction: Isotope Effects and Stereodynamical Control

The isotope effects and stereodynamical control in the C(¹D) + HD (v = 1, j = 2) insertion reaction are investigated using the time-dependent wave packet method, based on a high-precision neural network potential energy surface of CH₂(ã¹A′). The reaction probabilities at J = 0 exhibit no threshold and show pronounced resonance oscillations. Integral cross sections reveal that the CD + H channel dominates at low collision energies due to contributions from low partial waves. However, the CH + D channel becomes dominant above 0.43 eV as high partial waves take over, leading to an inversion of the product branching ratio. Stereodynamical analysis reveals that the parallel configuration significantly enhances the CH + D channel, while the perpendicular configuration suppresses it and weakly promotes the CD + H channel. Furthermore, the parallel alignment enhances forward and backward scattering for both product channels. Specifically, aligning the HD molecule parallel to the relative velocity lowers the critical collision energy required for CH + D dominance, thereby significantly amplifying its competitive advantage over the CD + H channel.