Nine-dimensional quantum dynamics study of the H2 + NH2 → H + NH3 reaction: a rigorous test of the sudden vector projection model

Reaction dynamics and mode specificity in the H-2 + NH2 -> H + NH3 reaction are investigated in full dimensionality on a recent ab in/ti based global potential energy surface. Integral cross sections from several low-lying vibrational states of both reagents have been calculated under the centrifugal sudden or J-shifting approximations, using an initial state selected time-dependent wave packet method. This nine-dimensional system provides an ideal proving ground to test our recently proposed Sudden Vector Projection (SVP) model. Our results indicate that vibrational excitation of H-2 enhances the reactivity. On the other hand, excitation of either the symmetric or antisymmetric stretching mode of NH2 inhibits the reaction, while excitation of its bending mode has a negligible effect. Furthermore, all vibrational modes are less effective than translational energy in promoting the reaction. These mode-specific features are rationalized with the SVP model.