Charge transfer into excited states of hydrogen atoms reflected on metal surfaces

Abstract

A theory of transfer of electrons into excited states of a proton moving above a free-electron metal surface is presented, based on a time-dependent Anderson Hamiltonian with a degenerate atomic level. The density matrices of the resulting atomic states are calculated. At grazing proton trajectories the parallel velocity effectively brings some of the conduction electrons into resonance with higher atomic levels. This mechanism leads to creation of excited states in which the sublevels within the shell are unsymmetrically populated. The polarization characteristics of Balmer ${\mathrm{H}}_{\ensuremath{\alpha}}$ light ($n=3$ to $n=2$ transition) emitted from 9-keV protons scattered at a few degrees are calculated, in good agreement with experimental data. The possible influence upon the electron capture process of the incompleteness of the screening of the fast proton by conduction electrons is discussed.