A study on negative ion formation in the scattering of a proton beam from two monolayers of Ba on Ag(111) surface is presented. The dependence of the negative ion yield on the polar scattering angle and azimuthal orientation of the crystal has been determined for beam energies from 500 to 1000 eV. In addition the yield of fast neutrals has been determined. Based upon a shadowing and blocking analysis of the angular distributions of the H- ions, it can be concluded that the Ba overlayer shows the same crystalline structure as the Ag(111) substrate. The recorded negative ion fractions can be explained by a simple model describing resonant charge transfer calculated by the non-perturbative CAM method and taking into account the parallel velocity effect.

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Journal Chem. Phys.
van Slooten, U, Teodoro, O. M. N. D, Kleyn, A.W, Los, J. H, Teillet-Billy, D, & Gauyacq, J. P. (1994). Negative ion formation in proton scattering from Ba/Ag(111). Chem. Phys., 179, 227–240.