Monte Carlo trajectory study of Ar+H2: Vibrational selectivity of dissociative collisions at 4500°K and the characteristics of dissociation under equilibrium conditions

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Abstract
We have used the quasiclassical trajectory method and a realistic potential energy surface to calculate rate constants and Arrhenius activation energies for dissociation of p-H2 in Ar from each of H2′s fifteen different vibrational levels at a rotational–vibrational temperature of 4500°K. We have also calculated the equilibrium rate constant and energy of activation and many other attributes of the equilibrium reaction at 4500°K. The effect of considering the seven quasibound states with longest unimolecular lifetimes as reactant states is also studied in detail. Reaction is favored by high internal energy—either high rotational quantum number at low vibrational quantum number or vice versa. In particular, at equilibrium the groups of vibrational levels with vibrational quantum numbers v equal to 0–6, 7–11, and 12–14 contribute 26%, 48%, and 26% to the reaction rate. Dissociation from low v levels proceeds primarily from the topmost j state for a given v level; as a consequence neither the assumption of vibrational equilibrium nor the assumption of rotational equilibrium is valid for treating nonequilibrium effects.