Nonadiabatic Reactive Quenching of OH( A 2 Σ + ) by H 2 : Origin of High Vibrational Excitation in the H 2 O Product.

The nonadiabatic dynamics of the reactive quenching channel of the OH( A 2 Σ + ) + H 2 /D 2 collisions is investigated with a semiclassical surface hopping method, using a recently developed four-state diabatic potential energy matrix (DPEM). In agreement with experimental observations, the H 2 O/HOD products are found to have significant vibrational excitation. Using a Gaussian binning method, the H 2 O vibrational state distribution is determined. The preferential energy disposal into the product vibrational modes is rationalized by an extended Sudden Vector Projection model, in which the h and g vectors associated with the conical intersection are found to have large projections with the product normal modes. However, our calculations did not find significant insertion trajectories, suggesting the need for further improvement of the DPEM.