Adsorbates effects in H$^{- }$ - Na/Cu(111) collisions

The (111) faces of Cu, Ag and Au present a band gap that extends just below the vacuum level at the $\overline \Gamma \quad {\rm g}$point [1]. The effect is to forbid electrons with energies in a certain range to be transferred into the metal along the surface normal. Thus, the presence of a band gap should dramatically influence various experiments in ion-surface collisions involving electron capture or loss. In recent years, this topic received a great interest [2 -- 4]. Adsorbates deposition makes the electron dynamics at such surfaces to be even more complex. We analyze some interesting adsorbates effects: (1) projectile energy levels and widths are strongly perturbed when this approaches close to an adsorbate atom; (2) scattering by adsorbates may be used to laterally confine surface state electrons; (3) adsorbates may enhance the band gap effect; (4) adsorbates tend to couple the surface states to the bulk states. Results for the H$^{-}$ projectile interacting with a Na/Cu(111) surface are reported. [1] E.V. Chulkov, V.M. Silkin and P.M. Echenique 1999 \textit{Surf. Sci. }\textbf{437, }330. [2] A.G. Borisov, A.K. Kazansky and J.P. Gauyacq 1999 \textit{Phys. Rev. B. }\textbf{59}, 10935. [3] H.S. Chakraborty, T. Niederhausen and U. Thumm 2004 \textit{Phys. Rev. A.} \textbf{70}, 052903. [4] B. Bahrim, B. Makarenko and J.W. Rabalais 2005 \textit{Surface Sci.} \textbf{594}, 62.