Monte Carlo trajectory study of Ar+H₂ collisions. II. Vibrational and rotational enhancement of cross sections for dissociation

Integral cross sections and properties of the dissociated trajectories were calculated for the reactions Ar + H₂→Ar + H + H and Ar + H ₂(qb)→Ar + H + H, where H₂(qb) is a quasibound H ₂. Integral cross sections were also calculated for Ar + H ₂ ⇌ Ar + H₂(qb). Twenty-four different (21 bound, 3 quasibound) initial vibrational-rotational states of H₂ are considered. The potential surface (which we presented previously) is based on modified statistical calculations at small distances and dissociates to an accurate potential in the van der Waals region and to accurate diatomic curves. At a total energy 1 eV above the energetic threshold for dissociation, we find reagent vibrational energy is very effective in promoting dissociation (the vibrational bias parameter of Kiefer, Joosten, and Breshears is about 11 to 13), rotational energy is second most effective, and relative translational energy is least effective. Except for the topmost vibrational level we find dissociation cross sections are much smaller than predicted by the hard-sphere available-energy theory.