How do hydrogen atoms on surfaces affect the trajectories of heavier scattered atoms?

The recently developed technique of scattering and recoiling imaging spectr ometry (SARIS) is used to probe the effect of hydrogen atoms on the traject ories of 5 keV Ne+ scattering from a Pt(111) surface. Classical kinematic c alculations and ion trajectory simulations, using the scattering and recoil ing imaging code (SARIC), are carried out in order to probe the details of the interaction and the nature of the perturbation. It is demonstrated that adsorbed hydrogen atoms are capable of deflecting these low kilo-electron- volt Ne trajectories scattering from a Pt surface. These perturbations resu lt in spatial shifts and broadenings of the anisotropic features of the SAR IS images that are readily detectable. The scattered Ne atoms lose 0-18% of their initial kinetic energy as a result of the perturbation by the H atom s. The physics of the perturbation on the trajectories can be understood fr om straightforward classical kinematic calculations and SARIC ion trajector y simulations. (C) 1999 American Institute of Physics. [S0021-9606(99)71148 -7].