The electronic stopping cross section {var_epsilon} of slow hydrogen projectiles in large-band-gap insulators has been measured at energies of a few keV. Even at velocities as low as v{sub 0}/3 (v{sub 0}=c/137) , we find no influence of the band gap on the velocity dependence of {var_epsilon} , contrary to the case of gaseous targets with similar minimum excitation energy. The magnitude of {var_epsilon} and its essentially linear velocity dependence allow us to arrive at the following conclusion: Electron promotion processes contribute substantially to stopping due to formation of molecular orbitals. This points towards the existence of a bound electron state at a proton that moves slowly in an insulator. A simple model based on the calculation of molecular orbital correlation diagrams for the H/LiF collision system supports the idea of local reduction of the band gap of an insulating target. {copyright} {ital 1997} {ital The American Physical Society}

Eder, K.; Semrad, D.; Bauer, P. [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet Linz, A-4040 Linz (Austria)] [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet Linz, A-4040 Linz (Austria); Golser, R. [Institut fuer Radiumforschung und Kernphysik, Universitaet Wien, A-1090 Wien (Austria)] [Institut fuer Radiumforschung und Kernphysik, Universitaet Wien, A-1090 Wien (Austria); Maier-Komor, P. [Target Laboratory, Technical University Munich, D-85748 Garching (Germany)] [Target Laboratory, Technical University Munich, D-85748 Garching (Germany); Aumayr, F. [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Wien (Austria)] [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Wien (Austria); Penalba, M. [Departamento de Fisica Aplicada I, E.T.S.I.I. y T., Universidad del Pais Vasco, Bilbao (Spain)] [Departamento de Fisica Aplicada I, E.T.S.I.I. y T., Universidad del Pais Vasco, Bilbao (Spain); Arnau, A.; Ugalde, J.M.; Echenique, P.M. [Departamento de Fisica de Materiales, Universidad del Pais Vasco, Apartado 1072, San Sebastian 20080 (Spain)] [Departamento de Fisica de Materiales, Universidad del Pais Vasco, Apartado 1072, San Sebastian 20080 (Spain)

1997-11-01