Collisions between rare-gas atoms at low-keV energies. II. Asymmetric collision systems: He-Ne, -Ar, -Kr, -Xe

Abstract

Elastic and inelastic collisions in the asymmetric He-$X$ ($X=\mathrm{N}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{A}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{K}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{X}\mathrm{e}$) systems are studied at low-keV energies (0.8-3.0 keV). The experimental method involves energy-loss measurements on the scattered particles using either a time-of-flight technique (for neutrals) or electrostatic energy analysis (for ions). Differential cross sections are reported and the results interpreted in a quasimolecular treatment of the collision. Of particular significance is the very low excitation and ionization of the helium projectile relative to excitation of the target. An understanding of this requires a modification of the usual diabatic correlation rules, and implies the promotion of the outer filled molecular orbital. Predictions made from the modified correlation diagram, and calculated potential-energy curves are found to agree with the experimental results.