Competition between the H- and D-atom transfer channels in the H 2 O + + HD reaction: reduced-dimensional quantum and quasi-classical studies.

The ion-molecule reaction between a water cation and a hydrogen molecule has recently attracted considerable interest due to its importance in astrochemistry. In this work, the intramolecular isotope effect of the H2 O+ + HD reaction is investigated using a seven-dimensional initial state-selected time-dependent wave packet approach as well as a full-dimensional quasi-classical trajectory method on a full-dimensional ab initio global potential energy surface. The calculated branching ratios for the formation of H3 O+ and H2 DO+ via H- and D-transfer agree reasonably well with the experimental values. The preference to the formation of the H3 O+ product observed using the experiment at low collision energies is reproduced by theoretical calculations and explained by a one-dimensional effective potential model.