Quasiclassical trajectory and statistical studies of atom exchange and dissociation in Ar+Ar2, Ar+Ne2, and Ar+ArKr collisions

Rare gas atom--diatom collisions of Ar+Ar2, Ar+Ne2, and Ar+ArKr have been investigated to determine the general features of exchange and dissociation reactions involving van der Waals molecules. Quasiclassical trajectory calculations on pairwise additive potential surfaces show that metastable dimers with internal energy above the dissociation limit of the dimer but below the rotational barrier play a major role in both the exchange and dissociation dynamics. Lifetime distributions for such metastables, obtained from WKB calculations, suggest that they will be of importance in crossed molecular beam studies of such systems as well as in nucleation studies. Computed branching ratios are found to approach statistical behavior at higher energies, but deviate significantly from such predictions at lower energies where the endothermic pathway involving exchange with the lighter atom is unexpectedly found to be favored. Product rotational state distributions are found to be governed largely by statistical factors. The distribution for metastable Ar2* dimers is found to be trimodal in character. Although such a result is predicted by a density of quantum states model, no classical explanation was found