Rotational Populations in ZnH/ZnD Products

Using ab initio multiconfigurational potential energy surfaces pertinent to the reaction Zn(P) + H2 ---> ZnH( Σ) + H and local surface tessellation and interpolation methods developed earlier, we carried out classical trajectory simulations of the title reactions, running large ensembles of trajectories with initial conditions representative of full-collision experiments. Then, using binning techniques, the ZnH/ZnD vibrational and rotational populations have been extracted. Our simulation results duplicate certain unexpected findings noted in experiments of Breckendrige et al. Specifically, it is observed that the rotational profiles found for ZnH produced from H2 or from HD are nearly identical, as are the ZnD populations obtained in reactions with D2 or HD. By interrogating the progress of reactive trajectories, we have been able to identify the origin of (much of) the rotational angular momentum in the ZnH/ZnD products which then allows us to put forth a physical model which, we believe, explains the unexpected ZnH/ZnD isotope effects in the product rotational profiles.