KINEMATIC MODEL FOR REACTION .2. ION-MOLECULE REACTIONS INVOLVING H2 AND D2

The kinematic model for atom-diatom reactions is extended to include ion-molecule reactions. In the extended model, reactants approach each other up to the point of contact along trajectories and with a relative velocity determined by the potential acting between them. After contact, energy and momentum transfers among the three particles are calculated assuming hard-sphere interactions; reaction probabilities are assigned on the basis of the results of the kinematic analysis. Reaction cross sections are calculated for the Ar++H2 and Ar++D2 systems for Ar+ energies in the ranges 20-200 eV and 10-100 eV, respectively. Good agreement with experiment is obtained. The model predicts a small isotope effect favoring the reaction of Ar+ with D2 over H 2 when compared at the same relative energy. Some qualitative features of the N2++D2, H2 reactions are shown to be consistent with the kinematic considerations of the model.