Quantum dynamics studies of isotope effects in the Mg⁺(3p) + HD → MgH⁺/MgD⁺ + D/H insertion reaction

The time-dependent wave packet quantum dynamics studies for the Mg⁺(3p) + HD → MgH⁺/MgD⁺ + D/H diabatic reaction are carried out for the first time on recently developed diabatic YHWCH potential energy surfaces [Phys. Chem. Chem. Phys., 2018, 20, 6638-6647]. The results of reaction probabilities and total integral cross sections show a dramatic preference to the formation of MgD⁺ over MgH⁺ owing to the insertion reaction mechanism in the title reaction. The MgD⁺/MgH⁺ branching ratio witnesses a monotonic decrease from 10.58 to 3.88 at collision energy range of 0.01 to 0.20  eV, and at the collision energy of 0.114  eV, it is close to the experimental value of 5. The rovibrational state-resolved ICSs of the two channels show the products MgD⁺ have higher vibrational excitation and hotter rotational state distributions. The opacity function P(J) suggests that the MgH⁺ + D channel and MgD⁺ + H channel are dominated by high-b and low-b collisions, respectively. Both forward and backward scattering peaks are found in the differential cross section curves, whereas the angle distributions of products are not strictly forward-backward symmetric because of the short lifetime of the complex in the reaction.