Backward ejected electrons produced by 1-MeV/u Oq+ (q=3--8) projectile ions colliding with argon gas

The cross sections for ejecting electrons into a cone of half-angle ∼2 degree centered on the backward direction have been measured as a function of electron energy for 1-MeV/u Oq+ (q=3--8) projectiles colliding with Ar. For O3+ and O4+ projectiles, the cross sections have also been measured in coincidence with exit charge states (q+1) and (q+2) of the projectile. A prominent feature in all spectra is a target LMM Auger peak. The cross sections for producing Ar LMM Auger electrons are nearly independent of projectile incident charge states. A projectile electron-loss peak is produced when the projectile brings loosely bound L-shell electrons into the collision. The shape of this peak is independent of the projectile exit charge state within experimental error. The measured electron-loss production cross sections at 180 degree are compared with the predictions of various on-shell approximations to the impulse approximation. Peak height and position are sensitive functions of the on-shell approximation used. The predictions of the elastic scattering model agree well with the data