Collision induced dissociation of Ar2. Details of the collision dynamics

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Abstract
The reaction Ar2+Ar→3Ar is a prototypical problem in the study of collision induced dissociation since (a) the Ar3 system is expected to behave classically for energies near and beyond the dissociation threshold and (b) the Ar2 pair potential has been determined very accurately from gas kinetic properties and molecular beam experiments. The exact three dimensional cross sections for dissociation and exchange are known from previous work. Here we consider two dimensional trajectories in an effort to assess the effectiveness of various collision geometries. All results refer to Ar2 initially in the ground state. We examine two specific types of initial configuration which we label orthogonal (⊥) and parallel (∥). Detailed opacity functions were calculated at several energies for each configuration. In addition we have carried out zero impact parameter calculations for the dissociation probability as a function of energy. One can conclude from these studies that long range forces significantly affect the collision dynamics and that the orthogonal configuration is more important and representative of the three dimensional results than the collinear model frequently used in dissociation studies.