Electron emission by Doppler-mediated formation of doubly excited H-** in grazing incidence of protons on clean Al(111)

We present a new electron emission process which may give rise to a structu re in electron energy distributions observed for grazing incidence of proto ns on atomically clean Al(111). It is conjectured that the formation of dou bly excited negative hydrogen ions H-** from the Doppler-shifted surface de nsity-of-states results in autodetached electrons which are scattered and d iffracted a he monocrystalline surface. This scenario is a modi cation of a recently suggested model which assumed electron production from elastic co llisions of projectiles with the free-electron gas at the surface and diffr action upon escape into vacuum. The here proposed process should be most si gnificant for hydrogen projectiles with comparably low energy (<10 keV).