One and two electron processes in collisions of highly charged ions with He at velocities around 1 a.u

We have studied one and two electron processes in collisions of Ar16+ and O8+ ions with He atoms at velocities between 0.23 and 1.67 a.u. These processes were identified by measuring the final charges of the projectile and recoil ions in coincidence. Single electron capture (SC) is the dominant process at all our velocities. Transfer ionization (TI), where the He loses both electrons but the projectile captures only one, is next largest. Double capture (DC) and single ionization (SI) are about 10 times smaller, with DC larger for Ar and SI negligible for O. None of these processes show any dramatic velocity dependence. The energy independence of SI is somewhat surprising as our measurements span the velocity region where ionization would be expected to increase. Our analysis suggests that the ionization process is being suppressed by SC and TI processes. The average Q-values for capture channels were determined by measuring the longitudinal momenta of the recoiling target ions. The Q-values for both SC and TI decrease with increasing projectile energy, which indicates that electrons are captured into less tightly bound states as the collision velocity is increased