Collisional excitation of CO by 2.3 eV H atoms

Vibrational and rotational distributions of CO excited by collisions with 2.3 eV H atoms have been obtained by monitoring the products with vacuum ultraviolet (VUV) laser induced fluorescence. Translational-to-vibrational (T → V) transfer is dominated by the dynamics of collisions occurring in the two wells on the H + CO potential energy surface, one characterizing the HCO radical and the other characterizing COH. The measured vibrational distributions agree well with the results of trajectory calculations performed on the ab initio potential energy surface of Bowman, Bittman, and Harding (BBH). The measured rotational distributions show two significant differences from the calculated ones. First, for v = 0 the experiments find more population in J < 15 than predicted. This discrepancy may be due to errors in the repulsive part of the BBH surface that is outside the HCO and COH wells, but inside the van der Waals well. Second, for v = 1, the experimental distribution is flat from J = 0 to J = 10, whereas the calculated one rises from near zero at J = 0 to a peak at J = 12. This discrepancy appears to be the result of an excessively high ab initio estimate (by a few tenths of an eV) of the barrier for H atom addition to CO to form COH.