Hydrogen anion formation by electron capture in collisions of hydrogen atoms with an Al(100) surface*

We theoretically investigate the electron transfer dynamics during the reflection of hydrogen atoms on an Al(100) surface for a wide range of collision energies below 6 $\sim$ keV. We find a non-monotonic variation of the hydrogen-negative-ion fractions as functions of the projectile impact velocity due to non-adiabatic electron transfer. Our calculated anion fractions for projectiles scattered along high Miller-index crystal-surface directions [1] are in good quantitative agreement with measured hydrogen anion fractions [2] for a wide range of exit velocities. \\[4pt] [1] B. Obreshkov and U. Thumm, Phys. Rev. A \textbf{83} 062902 (2011) and to be published.\\[0pt] [2] M. Maazouz, R. Baragiola, A. Borisov, V. A. Esaulov, S. Lacombe, J. P. Gauyacq, L. Guillemot, and D. Teillet-Billy, Surf. Sci. \textbf{364}, 568 (1996).