Projectile scattering in one- and two-electron transitions

Projectile angular distributions in one- and two-electron transitions in collisions of helium with energetic bare projectile impacts are discussed within the framework of Born and continuum distorted wave approximations. Characteristic critical scattering angles, due to projectile-electron interactions, are investigated under certain kinematical conditions in the projectile angular distributions. Only a single critical deflection, characteristic to the Thomas double-collision mechanism, is observed when a one- electron transition is considered, which is at variance with the recent experimental finding of an additional peak in the measured angular differential cross sections for single-electron capture in H+-He collisions (Gudmundsson et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 185209). Multiple scattering theories predict more than one projectile critical deflection only when two or more electrons participate in the processes. The analyses are performed both for ionization and capture reactions, where scattering quantities for the latter transitions are derived from the former ones using continuity of transition amplitudes across the ionization limit.