Mapping of the Bethe surface in single-ionization ion-atom collisions

The three-body Coulomb problem is explored using classical-trajectory Monte Carlo and continuum distorted-wave methods that include all interactions, including the nuclear-nuclear term. Calculations for low-energy electron emission as a function of projectile deflection, the Bethe surface, are compared with experiment for single ionization of He by 100 MeV u^-1 C⁶⁺ and 3.6 MeV u^-1 Au⁵³⁺. Good agreement is realized for the C⁶⁺ system. For Au⁵³⁺ poor agreement with experiment is obtained, indicating that the proposed lack of the nuclear-nuclear interaction is not the source of the discrepancy. The calculations further show that significant cross sections at large projectile deflections are only realized for double ionization, not single ionization.