Accuracy of the IOS approximation for highly inelastic RT collisional energy transfer. CO-Ar

Abstract

Rate constants for rotational excitation of CO by collisions with Ar atoms have been computed within the infinite order sudden (IOS) approximation and compared with values from exact classical trajectories. For CO-Ar, as for COHe, accurate values for R(O → j) - at least for small and intermediate j - may be obtained by taking the geometric average of rates computed assuming the IOS energy is the initial energy for upward O → j transitions and the initial energy for downward j → O transitions. however, especially for higher j, it appears preferable to interpret the IOS energy as the final kinetic energy. The best overall results are probably obtained by averaging rates computed assuming the IOS energy is the final energy for upward transitions and the final enery for downward transitions.