Direct observation of the initial-state distribution of the first electron transferred to slow highly charged ions interacting with a metal surface

The electron transfer process in the interaction of a slow highly charged ion with a metal surface has been studied employing a microcapillary foil as a target. The combination of the target and a visible light spectroscopy allows us to directly evaluate the initial (n,l) distributions of the first transferred electrons. It was found that observed lines were primarily attributed to Δn=1 transitions with relatively high angular momenta (li > or approx. 4). A cascade analysis revealed that the electron is selectively transferred to n≅qin+1 states with a narrow distribution width of δn≅2 (full width at half maximum). The average initial principal quantum number is consistent with the prediction of the classical over-barrier model