Investigation of the planar H + H2 reaction near threshold

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Abstract
We report a study of the quantum dynamics of the hydrogen exchange reaction for collisions in which the nuclei move in a single plane throughout the reaction. Our efforts are concentrated at the reaction threshold, for it is here that classical dynamics is least accurate, and yet it is also this region that contributes most heavily to thermal rate constants. Because transition amplitudes in the threshold region are uniformly small, the distorted wave approximation should provide an adequate description of the dynamics. Assuming the ground vibrational state for all molecules, we compute elements of the scattering (S) matrix for several rotational transitions. From the S-matrix elements, we compute reaction probabilities, angular distributions of products (the differential cross section), and the total reaction cross section. The reaction probabilities indicate that reaction is most likely to occur at small impact parameters. The differential cross sections are strongly back peaked, implying that the product molecule recedes in the direction from which the incoming atom approached. Contrary to an earlier study of this reaction, we observe no forward peaking in the differential cross sections.