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

Abstract

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 $(n,\ensuremath{\ell})$ distributions of the first transferred electrons. It was found that observed lines were primarily attributed to $\ensuremath{\Delta}n=1$ transitions with relatively high angular momenta $({\ensuremath{\ell}}_{i}\ensuremath{\gtrsim}4)$. A cascade analysis revealed that the electron is selectively transferred to $n\ensuremath{\approx}{q}_{in}+1$ states with a narrow distribution width of $\ensuremath{\delta}n\ensuremath{\approx}2$ (full width at half maximum). The average initial principal quantum number is consistent with the prediction of the classical over-barrier model.