We have investigated electron emission for transfer ionization (TI) and total electron emission, for He and H2 targets. Double differential cross sections in angle and energy of the ejected electrons have been obtained covering the angular range from 0° to 175° and energies from 2 to 140 eV. Pure ionization differential cross sections, derived by subtraction, show an increasing contribution to the electron emission at low energies. The main observed structure, a cusp in the forward direction for electrons emitted with velocities close to the incident projectile velocity, presents a symmetric shape for TI. This fact, together with the similar shape of the cusp for both He and H2 targets, suggest the presence of a two-electron intermediate state centred at the projectile leading to cusp formation in TI. The cusp for pure ionization, in contrast, shows a strong asymmetry, and a different shape for each target. The differential electron emission measurements allow us to estimate the cross sections for capture to doubly excited states resulting in autoionization of the projectile, which contributes to the TI channel. We obtained a much larger cross section value for H2 than for He targets, in contrast with known cross sections for true double capture having the same order of magnitude for both targets.

In this work we present a theoretical study of the single ionization process involved in collisions of protons on He, Li, and Be targets at 2 MeV/ amu projectile impact energy. Fully differential cross sections ͑FDCSs͒ are calculated within a continuum distorted wave method. Three different potentials are used to represent the interaction between the low energy outgoing electron and the residual ion target. Two of them are based on Coulomb potentials with proper effective charges for the target, while the other relies in a Garvey-type potential. These procedures provide remarkable differences in the binary and recoil peak regions, for the Li and Be cases. On the other hand, He target calculations lead to qualitative agreement for the three FDCSs at the momentum transfers and emission energies here considered. These results manifest the complexity of the ionization process for multielectronic targets and emphasize the importance of choosing an adequate model potential to describe the emitted electron dynamics in ionizing collisions.

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