Double ionization of a negative hydrogen ion by positron and electron impact athigh and intermediate energies

Abstract

Double ionization (DI) of a negative hydrogen ion (H−)has been studied in a comparative manner by e and e+ impactsat high and intermediate incident energies using the framework of the Coulomb–Bornapproximation. Unlike other existing theories for the DI process of H−, thepresent model is the first one to take account of the residual Coulomb potential betweenthe projectile and the ionic target and as such distinguishes between the e and e+results (fully differential cross sections), thereby allowing for the study of thecharge asymmetry in such DI processes. Furthermore, due to the neglect of thelong-range Coulomb interaction between the incident e/e+ and the targetH−ion in both the channels in the previous models, the perturbing potential does notvanish asymptotically with these approaches and the wavefunctions do not satisfy theproper asymptotic boundary conditions for the particular ionization process. Thepresent model is free from this defect. The expected symmetry about the ±q (momentumtransfer) direction in the first-order theories is broken in the present model, indicatingthe presence of non-first-order effects. Deviations from the dipolar limit (q → 0) for optical transitions(γ, 2e)are also discussed. This behaviour corroborates with the experimental findings forinert gas targets, there being no experiments for the (e, 3e) of H− asyet. Results are presented for some selected kinematics (both symmetrical andasymmetrical) chosen in accordance with the experiments on the (e, 3e) process ofinert gas targets.