Neutralization of fast protons after grazing scattering from AI(111)

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Abstract
We investigate the neutralization of fast protons (4 to 200 keV) after the interaction with a clean AI(111)-surface at grazing incidence (Φ < 1°). At projectile velocities of about 0.4 v 0 (v 0 = Bohr velocity) we observe almost total neutralization, while the neutral fraction decreases down to 2% at about 3 v 0. Model calculations in the framework of resonant electron transfer, which describe the charge exchange of alkali–ions at an aluminum surface fairly well, predict a much stronger decrease of neutralization with increasing projectile velocity than observed. We interpret this discrepancy by the presence of further electron capture mechanisms like Auger-neutralization, etc. The yield of negative ions is lower than 1% at all velocities and is satisfactorily reproduced by theory of resonant electron transfer.