Experimental investigation of the mechanisms creating projectile continuum electrons in highly charged ion-atom collisions

Abstract

Different collision mechanisms, which create continuum electrons that are slow in the rest frame of the ion, have been investigated by zero-degree electron spectroscopy. For the four-electron ions C2+, O4+ and F5+, (1s2s2) colliding with Ar autoionisation occurs after double-core excitation at high impact velocities. The combination of transfer and excitation, however, becomes an important mechanism, leading to autoionisation at lower impact velocities. For the three-electron ion F6+, (1s22s) autoionisation lines were observed only as a result of transfer and excitation in the velocity interval from 3 nu 0 to 8 nu 0 considered. For 20 MeV Auq+ on H2, He, and Ar (5<or=q<or=19), zero-degree electron energy spectra were measured in coincidence with charged-state-selected exit ions. The observed autoionisation lines are due to transfer and excitation. The cusp electrons originate from several processes: electron loss to the continuum (q low), electron capture to the continuum, and transfer ionisation. Cross sections for the different collision processes, giving rise to continuum electrons, were obtained.