Cusp-electron production in collisions of open-shell He-like oxygen ions with atomic targets

Abstract

We report on double differential cross sections of cusp electrons obtained in MeV/u collisions of open-shell He-like oxygen ions with helium. We use zero-degree electron spectroscopy and our double measurement technique, involving ${\mathrm{O}}^{6+}(1{s}^{2})$ ground-state and ${\mathrm{O}}^{6+}(1{s}^{2},1s2s)$ mixed-state beams, to extract the cusp contribution from only the excited ${\mathrm{O}}^{6+}(1s2s)$ beam. Theoretical calculations based on the continuum distorted wave eikonal initial state are in very good agreement with the measurements. The roles of the processes of electron capture to the continuum, electron loss to the continuum, and electron loss to the continuum with simultaneous target ionization, which contribute to the cusp peak, are discussed in detail.