IOSA investigations of the effects of potential surface topography upon elastic and inelastic scattering and rotational relaxation in the (He, CO2) system

Abstract

The effect of potential surface topography upon elastic and inelastic scattering has been investigated using the infinite-order sudden approximation (IOSA) to compute total differential and integral cross sections, state-to-state cross sections, and the relaxation rates of depleted levels in the (He, CO2) and (3He, CO2) rigid rotor systems on six different potential energy surfaces that include three surfaces obtained from electrom–gas type calculations, two ab initio SCF surfaces, and one surface (KPK) obtained by empirical fitting to the measured total differential cross section. It is found that the total elastic, inelastic, and differential cross sections are very sensitive to the long-range attractive terms in the potential, and the differential cross sections are also found to be significantly dependent upon the topography of the repulsive regions of the surface. Consequently, differential cross sections are very sensitive probes of surface topography and should be the data of choice for purpose of empirical adjustment of a surface. In contrast, the relaxation rates of a depleted rotational level are found to be insensitive to the details of the surface. In addition, the relaxation rate and total inelastic cross section out of state j are found to be almost independent of the particular j state involved. Consideration of the microscopic details leading to these results suggests that similar behavior will be observed in other systems that are nearly classical with closely spaced energy levels. Of the surfaces investigated, the KPK surface gives results that are in closest agreement with experiment. The electron–gas and SCF surfaces, when augmented by a van der Waals attractive term, give similar results which are almost as good as those obtained on the empirically adjusted KPK surface. This suggests that a reasonable surface for a closed-shell system can be obtained by either procedure. The IOSA results for the relaxation rates and total inelastic cross sections are found to be in excellent agreement with quasiclassical trajectory calculations. However, the degree of agreement for quantities associated with state-to-state transitions is reduced.