Scattering of molecular and atomic hydrogen ions from single-crystal surfaces

Energy spectra of H₂⁺ molecules and of the resulting H⁺ ions backscattered from Ni(111) and W(100) surfaces are measured for incident H₂⁺ molecules in the energy range from 200 eV to 2 keV. Comparison is made to spectra obtained from incident H⁺. It is shown that the dissociation of the impinging molecular ions is not caused by an electron-loss process, but proceeds via excited molecular states. The dissociation probability may depend on the surface structure, which is concluded from pronounced changes of the ion yields with the orientation of plane of scattering relative to the crystal surface.