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

Elastic and inelastic collisions in the asymmetric He-X (X=Ne,0ex0exAr,0ex0exKr,0ex0exXe) 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.