``Step-up" vs. ``Step-sown" scattering asymmetry in the charge transfer of H$^-$ on free-electron vicinal metallic surfaces

We present numerical results based on a wave-packet propagation study of the one-electron charge transfer between H$^-$ ions and free-electron vicinal metallic surfaces [1]. We derive an effective potential for the motion of the active electron within a Thomas-Fermi-von Weizs\"{a}cker model and extend this model to include the image charge effects. We first calculate H$^-$ affinity level shift and width in fixed-ion approximation and solve a rate equation for the ion-survival probability for projectiles that are incident with a kinetic energy of 50 eV. We find an enhancement of the electron loss near the steps of the surface, due to the Smoluchowski effect. As a consequence, the ion-survival is more likely if the projectiles approach steps from above than from below [2]. \newline \newline $[1]$ B.~Obreshkov and U.~Thumm, Phys. Rev. A {\bf 74}, 012901 (2006). \newline $[2]$ B.~Obreshkov and U.~Thumm, Surf. Sci. {\bf 601}, 622 (2007). \newline \newline Supported by NSF and the Division of Chemical Sciences, Office of Basis Energy Sciences, Office of Energy Research, US DoE.