Quantum calculations of inelastic and dissociative scattering of HCO by Ar

Abstract

Quantum inelastic scattering calculations of Ar+HCO are reported using a new global potential, based on ab initio calculations. The infinite-order sudden approximation is used to describe the slow CO-axis rotation of HCO (which is approximately the top A axis), together with a coupled-channel treatment of the H-atom rotation about the A axis (with associated quantum number K), and the HCO vibrations. Pure ΔK transitions are examined for K=0, ΔK=1, 2; K=1, ΔK=−1, 1; and K=2, ΔK=−1, −2, for several low-lying vibrational states. Overall, the pure ΔK-changing cross sections are large and approximately the same for these vibrational states. However, for the same ΔK, the smaller initial K gives a larger inelastic cross section, and negative ΔK results in larger cross sections than positive ΔK. For vibrationally inelastic scattering, the present results are qualitatively in agreement with previous calculations, which used a standard sum-of-pairs (Lennard-Jones) Ar–HCO interaction potential [B. Pan and J. M. Bowman, J. Chem. Phys. 103, 9661 (1995)]. But quantitatively, the present vibrationally inelastic transition cross sections are roughly ten times smaller than these earlier ones. We attribute this to the use of the empirical interaction potential surface in those calculations. The coupling between the H-atom rotation and some vibrational modes can have a significant effect on the magnitude of the inelastic cross section. This is shown in detail for the transition from the initial state 4νb. The initial state-specific average energy transfer is also calculated, and ranges from −5 to 15 cm−1. Dissociation cross sections are also calculated for several initial states and one orientation angle of the CO axis. The contribution of resonance and nonresonance states to dissociation is assessed.