A quasiclassical trajectory study of OH rotational excitation in OH+CO collisions using ab initio potential surfaces

We have performed large basis set configuration interaction calculations to characterize the two potential surfaces (²A′ and ²A″) which correlate to the ground state of OH + CO. Only planar geometries of the four atoms are considered, and the calculations restrict the OH and CO bond distances to their isolated diatomic values. Global representations of these potential surfaces have been developed and used in quasiclassical trajectory studies of rotational excitation in low energy (1-6 kcal/mol) collisions of OH and CO in their respective rovibrational ground states. We find that the collisional excitation cross sections are about equal for the two surfaces, and there is a monotonic increase in each cross section with translational energy. For OH rotational quantum numbers N between 2 and 6 there is approximately a factor of 2-3 decrease in the cross section for each unit increase in N. The energy and N dependence of these cross sections are generally in excellent agreement with recent experiments. We have also explored the sensitivity of these cross sections to the nature of the potential energy surface, and we have used a surface that describes the formation of the intermediate complex HOCO to determine sensitivity of the rotationally inelastic cross sections to complex formation. In agreement with the experiments, we find that the low energy, high N cross sections are appreciably perturbed by complex formation.