A quasiclassical trajectory study of collisional excitation in H + CO

The results of a quasiclassical trajectory calculation of cross sections for collisional excitation in H (D) + CO at 1-4-eV translational energy are presented and used to interpret recent laser photolysis measurements. A realistic potential energy surface was used in these calculations based on Dunning's recent ab initio studies. Overall agreement of the calculated results with experiment is generally good, and this enables us to assess in detail what features of the potential energy surface the measured results are sensitive to. For the rotationally summed vibrational distributions, we find that the high v tail of these distributions is almost exclusively due to collisions which form a COH complex. The average COH lifetime is found to be about 3 OH vibrational periods, and the cross sections for complex formation are found to be very sensitive to the H + CO → COH barrier. Based on comparisons with experiment we revise this barrier from Dunning's 1.72-eV value down to 1.52 eV. Many other features of the measured results, such as the average vibrational energy transfer, are found to be primarily sensitive to impulsive collisions of H with either the C or O atom. Although the HCO portion of the potential surface was sampled with significant probability, none of the HCO complexes formed had a lifetime of more than one inner turning point. The rotational distributions were found to be composed of a high j component (for which 〈j〉 increases with increasing v) arising from impulsive collisions of H with the C atom, and a lower j component (for which 〈j〉 is constant or decreases with increasing v) arising mostly from collisions with the O atom.