Superelastic scattering of electrons from metastable He-like C4+ and O6+ ions -: art. no. 042709

Superelastic scattering, a collision process in which the scattered electron gains energy, has been investigated for metastable C4+(1s2s S-3) and O6+(1s2s S-3) He-like ions colliding with quasifree H-2-target electrons. The measured superelastic-scattering cross sections for 1s2s S-3-->1s(2) S-1 deexcitation show a strong dependence on the collision energy and the atomic number of the He-like ion. R-matrix calculations for the time-reversed equivalent process of electron-impact excitation are compared with the measured cross sections through the principle of detailed balance. In these calculations, the impulse approximation is utilized in conjunction with the Compton profile of the target electrons for the collisions of ions with quasifree electrons studied here. Calculations were performed taking into account the anisotropy of the cross sections as a function of the scattering angle, which equals 180degrees in the projectile rest frame for the reported measurements. Comparison between theory and experiment was used to infer the metastable 1s2s S-3 fraction in the incident He-like beam.