A quasiclassical trajectory study of H+CO2: Angular and translational distributions, and OH angular momentum alignment

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Abstract
We present a quasiclassical trajectory study of the H+CO 2 reaction dynamics, with emphasis on product angular and translational distributions, and OH angular momentum alignment. A new potential surface has been developed for this study, based on modifications of a previously developed full dimensional empirical HCO 2 potential surface. The modifications include correcting errors that cause the HO⋅⋅⋅CO dissociation barrier to be too loose, and adjusting the depth of the HCO 2 minimum and the heights of several barriers, in order to bring them into agreement with their best estimates determined from ab initio calculations. We compare cross sections, energy partitioning, and mechanistic information calculated using the unmodified and modified surfaces with experimental results. Results from the modified surface improve the comparison with experiment for the product OH energy partitioning, but the product CO internal excitation is still high. The translational distributions have the same shape as measured distributions, and the average translational excitation matches some experiments but is lower than others. The angular distribution calculated at 2.6 eV on the modified surface is in good agreement with experimental results, showing both forward and backward scattered peaks, with a slight preference for backward scattering. By studying the average lifetime of the HOCO collision complex, we find that the lifetime is comparable to the rotational period so that there is considerable forward scattering (half rotation) and backward scattering (full rotation). The OH product angular momentum alignment indicates no preference for polarization of the OH rotational angular momentum vector. This result–an essentially isotropic distribution–agrees within the experimental uncertainty for measurements of OH Π(A′) polarization dependent differential cross sections and center-of-mass frame alignment parameters, but not with OH Π(A″)