Transfer excitation in collisions of positrons with He and alkaline-earth metals

Positronium formation in positron-He(1s(2)) and positron-alkaline-earth met als is studied at high-enough impact energies. The importance of simultaneo us excitation of the target is analysed in comparison with the case where t he residual target relaxes to its fundamental state. A four-body version of the continuum-distorted-wave-final-state model is introduced to describe t his two-electron process, where in the case of alkaline-earth metals, the c ore formed by the target nucleus and the inner-shell electrons is assumed t o remain frozen during the collision. Cross sections of electron capture fo r selective final states and total cross sections are calculated to illustr ate our analysis.