ENERGY-LOSS H-2(+) IONS UNDER GLANCING-ANGLE INCIDENCE ON A SNTE(001)SURFACE( FRAGMENTS ARISING FROM DISSOCIATION OF FAST H)

Energy losses of H+ fragments repelled parallel and antiparallel to th e beam direction at dissociation are measured for a glancing-angle inc idence of 0.15-0.6-MeV/amu H-2(+) ions on a clean (001) surface of SnT e. The sum of the energy losses of the specularly reflected fragments is larger than twice that of protons of the same velocity reflected fr om the surface. For the interpretation of the vicinage effect on the s topping power of the surface, the energy losses of the pairs of fragme nts resulting from the dissociation of H-2(+) are calculated at the gl ancing-angle scattering. The contribution of single-electron excitatio n to the energy-loss of the pair is calculated with the harmonic-oscil lator model [J. Basbas and R. H. Ritchie, Phys. Rev. A 25, 1943 (1982) ] and that of collective excitation by the superposition of surface wa kes of two protons. A dependence of the vicinage effect on the distanc e from the surface is found from the calculated stopping powers-where the pronounced effect becomes weak as the distance decreases. The calc ulated energy losses of the reflected pairs of protons agree fairly wi th those measured. The agreement of the calculated energy losses with those measured supports the calculated dependence of the vicinage effe cts.