Surface-plasmon-assisted electron capture in H+/Mg and H+/Al collisions

We analyze the velocity-dependent threshold behavior of the transition rate for the surface-plasmon mode of proton neutralization at metallic surfaces. Consideration of the proton velocity, which had not been considered so far, affects the transition rates in a nonnegligible way. In particular we study the opening of the collective channel for the H+/Al system, which remains closed in the fixed ion approximation. Preliminary calculations of neutral fractions, after grazing incidence collision of a proton beam with an Al(1 1 1) surface, seem to indicate that the collective mechanism starts to play a significant role for impact velocities greater than 0.5 a.u.