On the role of ion-trajectories on confinement and recapture effects in the survival of anions scattered from metal surfaces

Resonant charge transfer in ion-surface collisions is a classic tool to explore surface electronic structures. Using the Crank-Nicholson propagation [1] we solve the time-dependent Schroedinger equation to simulate the electronic motion during collisions of H$^{- }$with Li(110) and Pd(111) surfaces. It was previously shown that the ion's survival after the collision depends (i) adiabatically (that is at slow ion-speeds normal to the surface) on electrons' confinement in metal band gap and (ii) diabatically on recaptures from image states [2]. We now find that for larger distances of closest approach (DCA) of the ion the image interaction accesses the adiabatic region and dominates the band-gap effect. In a real collision, the flight-trajectory determines the DCA as the metal-lattice repels the ion, resulting in a reduction in ion speed. Hence the trajectory induces a competition between various effects that is found to significantly modify the ion-survival phenomenology.\\[4pt] [1] Chakraborty et al., \textit{Phys. Rev.} A \textbf{70}, 052903 (2004);\\[0pt] [2] Schmitz et al., \textit{Phys. Rev.} A \textbf{81}, 042901 (2010).