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).