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The double electron capture into the continuum states of the projectile (double ECC) is investigated theoretically in collisions of 100 keV He2+ ions with He atoms. The process is described within the framework of the impact parameter and frozen-correlation approximations where the single-electron events are treated by the continuum distorted wave method. On the other hand, the Wannier theory is employed for describing the angular correlation between both ejected electrons. This treatment substantially improved the agreement between the theory and experiment as compared to the previous version of the theory (Gulyás et al., 2010) in which the correlation between the ejected electrons was taken into account by the Coulomb density of states approximation. Fil: Barrachina Tejada, Raul Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Gulyás, L.. Hungarian Academy of Sciences; Hungría Fil: Sarkadi, L.. Hungarian Academy of Sciences; Hungría

Protonium (Pn) annihilates almost instantaneously when its initial high-l states (l denotes the angular momentum) are transferred to the low-lying s, p or d states. In this work, the annihilation of Pn induced by electron or proton impact is described in quantal and semi-classical close-coupling methods, where the scattering wave functions are expanded in terms of Pn orbitals. The chain of transitions is found to be dominated by the dipole transitions at low impact velocities, while at high energies, contributions from non-dipole terms have to be considered for the proper description of the phenomena. In the case of proton impact, distant and close collision mechanisms govern the process at low and at high impact energies, respectively. The cross sections calculated for the proton projectile scale according to the rule established recently [K. Sakimoto, J. Phys. B: At. Mol. Opt. Phys. 38 (2005) 3447]. However, this scaling rule, except for initial p states at high energies, cannot be confirmed in the case of electron impact.

Doubly differential cross sections for single ionization of various targets are calculated using the CDW-EIS model which was recently extended to include Hartree-Fock wavefunctions for the target bound and continuum states. These results are compared with experiments using light and highly charged bare ions at high impact energies. Very good agreement is obtained in all the angular range. The asymmetry of the soft-collision electron peak in this energy range is also studied. The theoretical results show a large target dependence.

Angular distributions of ejected electrons in fast N 7+ + Li collisions have been measured. By calculating the individual amplitudes in a multipole expansion, we evaluate the relative importance of dipole transitions. Using a Li target, we find the relative importance of dipole transitions to depend strongly on the initial state.

We analyze in detail the single ionization of He by 3.6 MeV/u ions. The doubly differential cross sections as a function of impact parameter at fixed values of the electron energy are used to determine the average interaction range for different values of the projectile charge. It is seen that while for proton impact the interaction range varies very little with the electron energy, huge variations are observed for highly charged ions.

The continuum-distorted-wave-eikonal-initial-state model is applied to the calculation of doubly differential cross sections for electron emission in collisions between 100 keV protons and He, Ne and Ar atoms. A new code including a Hartree-Fock representation of bound and continuum wavefunctions of the multielectronic targets is used. A critical discussion of the experimental data available is presented.

The aim of the present study was to measure the double differential cross section (DDCS) for the electron ejection as a function of electron energy at 0° observation angle in H + → He collisions. Having in mind that the experimental and theoretical shape parameters of the DDCS known in the literature are rather scattered, we made a systematic study in the projectile energy range 75–1400 keV. The total electron yield and the shape parameters of the DDCS were determined and compared with the corresponding values from 2nd order OBK, CDW and CDW-EIS theories. A further aim of this work was to check whether the velocity of the projectile and that of the electrons at the maximum of the cusp peak are indeed equal.

The shape of the cusp was investigated by two different methods, namely by the measurement of DDCS in the angular region around 0° (contour lines) and by means of coincidences between the electron and the outgoing projectile for the impact of light projectile ions carrying electron(s). In the case of both methods a definite asymmetry of the cusp was found in contradiction with theoretical predictions. By using the coincidence method the contribution of the ECC and ELC mechanism was determined for different collision systems and it was found to be surprisingly high for ECC.