A close-coupling study of collision-induced dissociation: three-dimensional calculations for the He+H 2→He+H+H reaction

Abstract

Three-dimensional quantum mechanical close-coupling calculations using discretized continuum states have been carried out for the He+H 2→He+H+H collision-induced dissociation reaction in order to study the contribution of sequential two-body and direct three-body collisions just above the dissociation threshold. Although the calculations were done only for zero total angular momentum, we have found that the nonresonant, direct three-body mechanism is generally dominant for collisions of H 2 having a low rotational quantum number and that the two-body mechanism via quasibound resonance states is important only for H 2 having a higher rotational quantum number. We have also found that the magnitude of the total collision-induced dissociation probabilities is exclusively determined by the energy difference between the rovibrational energy level of H 2 and the dissociation threshold. This indicates that collision-induced dissociation can be described with a simple collisional energy transfer process. The semiclassical calculations, in which the relative radial motion is treated in classical mechanics while the other motions are treated quantum mechanically, have also been performed for comparison. We found that the semiclassical method does not work well for dissociation processes with small probabilities, as expected.