Charge transfer of slow highly charged xenon ions in collisions with magnesium atoms

We report an experimental study of the charge-transfer process in collisions of Xe${}^{q+}$ ions ($16\ensuremath{\le}q\ensuremath{\le}20$) with magnesium atoms at an energy of 5.5$q$ keV. With charge-selective and time-coincidence techniques, we separated the pure capture and capture accompanied by transfer-ionization processes. The experimental data indicate that the magnesium target is around two times more likely to lose two electrons than one in the collision. This finding is very different compared to the calculation based on the extended classic over-the-barrier model. The Xe${}^{q+}$-Mg collision also behaves very differently from ``traditional'' collisions between highly charged ions and noble gases. We suggest a one-step dielectronic mechanism for the capture process. The data also show that autoionization dominates the relaxation process after the capture, and fluctuation of the autoionization fraction versus the projectile charge state indicates that for the relaxation processes, the projectile core structure plays a more important role than the detailed characteristics of the projectile states where the target electrons are initially captured.