Thomas Process and Wave Function Imaging in P-He Transfer Ionization Investigated by Coltrims

Abstract

One of the fundamental capture mechanisms for fast ion atom collisions was proposed by L.H. Thomas in 19271 based on a classical treatment and observed by Palinkas et al,2 for the first time. This Thomas process can be understood as two consecutive binary collisions, first by the projectile with one of the target electrons and, second, between this electron and either the target nucleus (e-N-Thomas-scattering) or another target electron (e-e-Thomas-scattering). The e-e-Thomas-scattering offers a unique possibility to investigate dynamic electron-electron- (e-e-) correlation in atomic collision processes. For fast proton impact the perturbation of the target (in our case helium) is small and the electrons are quickly removed from the bound state by the e-e-Thomas-scattering. The e-e-Thomas-scattering always leads to a double ionization of the target, while the capture can either be to a bound (transfer ion-ization, TI) or a continuum state of the projectile³. Thus this process will leave the nucleus behind with its momentum distribution from the initial ground state, which mirrors the sum momentum of the 2 electrons. Furthermore the absolute probability for that process yields information on the spatial distribution of the two electrons.