Dynamics of the O+–H2 reaction. II. Reactive and nonreactive scattering of O+(4S3/2) at relative energies above 13 eV

Abstract

We report velocity vector distributions for the reactive and nonreactive scattering of O⁺ by H₂, D₂, and HD in the relative energy range 13–50 eV. Essentially no very small angle reactive scattering is observed for any of these systems. In the lower and intermediate parts of the energy range, the product of the O⁺(D₂, D)OD⁺ reaction reaches a maximum intensity near 50°, and decreases somewhat at larger angles. This shape is maintained but with decreasing intensity from 15–30 eV relative energy. At higher energies, the distribution moves to larger angles and the intensity continues to drop. From 13–20 eV, OH⁺ from O⁺–HD collisions peaks near 35°, and has little intensity at larger angles, while the corresponding OD⁺ product rises to a broad miximum near 90°, and is only slightly less intense at larger angles. At relative energies above 13 eV the nonreactive scattering of O⁺ has a major component that corresponds to the elastic impulsive scattering of O⁺ from one atom of the target. Nonreactive scattering from HD shows two peaks which correspond to impulsive O⁺–H or O⁺–D collisions. The experimental results are compared to the predictions of a model in which reaction occurs as the result of those sequences of two‐body hard sphere interactions which lead to bound product molecules. The general forms of the product angular distributions and their dependence on the isotopic composition of the target are fairly well represented by the model. For other features such as the experimental energy dependence of the total cross section ${\mathrm{(\sigma \; \propto \; E}}_{\mathrm{rel}}^{\text{−7/2}})$ and the corresponding isotope effect, the model is less successful. A convenient velocity vector diagram method is given which allows a simple, edifying analysis of product angular distributions to be made with a compass and straightedge.