Transfer and excitation in high-energy He+-He collisions: V.Electroniccontinuum influence on ejected electron distributions and TE crosssections

Abstract

Compared to experimental data based on 0° electron spectroscopy, previous theoretical predictions related to simultaneous transfer and excitation (TE) processes occurring in collisions between fast He+ projectiles and helium targets are not fully satisfactory. In fact, peaks in energy distributions of forward-emitted electrons have always been considered as the result of the production of (bound) doubly excited states followed by post-collisional Auger decay. However, two indistinguishable collision channels, hereafter referred to as TI, can also produce forward-ejected electrons: (a) direct target ionization and (b) simultaneous electron transfer and projectile ionization. They are ignored in these first studies, although experimental electron spectra show asymmetrical profiles. Here the TE process is re-examined within the framework of the continuum distorted wave with four-body (CDW-4B) formalism. Our approach sticks to Fano's description of a resonance, i.e. the adjacent electronic continuum of a doubly excited state produced during the collision is included. Very good agreement is found between the present predictions and the experimental data both for energy distributions of ejected electrons and for so-called total TE cross sections. Further, it is shown that TE cross sections, which are extracted directly from lineshapes, always contain non-separable contributions from the two above-mentioned TI channels.