The four-particle process of proton-helium transfer ionization has been studied using cold target recoil ion momentum spectroscopy to measure the momenta of all three particles in the final state. Most of the electrons are emitted in the H0 scattering plane and in the backward direction. The final state momentum distributions show discrete structures very different from those expected for uncorrelated capture and ionization. The measured momentum pattern is interpreted to be due to a new transfer ionization reaction channel which results from strong correlations in the initial He ground state momentum wave function.

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p+Na collisions have been investigated theoretically and experimentally at impact energies in the keV regime. We present results for capture and ionization processes, and, in particular, analyse the role of initial inner-shell electrons, whose active participation is identified in the experiments through the analysis of recoil-ion momentum spectra. Quantum-mechanical calculations within the independent particle model have been carried out for all active electrons. A very good overall agreement between the theoretical and experimental results is found. The calculations support the observation that capture from inner shells is an important reaction channel even at relatively low impact energies, and dominates total capture above 40 keV.

Ionization and electron transfer in collisions of bare ions from neutral target atoms with many active electrons are investigated within the independent particle model. We propose a simple model for the inclusion of time-dependent screening effects and discuss the question of how to analyze the solutions of the singleparticle equations in order to avoid fluctuating transition probabilities, which normally occur when the effective mean-field potential depends on the propagated orbitals. The basis generator method is used to solve the single-particle equations for the He 2ϩ ϩNe collision system in the energy range of 5 to 1000 keV/amu. It is shown that time-dependent screening effects reduce the cross sections for ionization and capture at low and intermediate impact energies significantly. Good overall agreement with experimental data is found except for the higher final charge states of the target ion.