EXCITATION AND LOSS PROCESSES OF IONS AT SURFACES

Experiments with atomic ionic and neutral particles, scattered at graz ing incidence from surfaces, lead to the conclusion that in the solid a large number of electron-hole pairs is excited. These excitations ca use energy losses and straggling which are measured in the energy rang e from 100 eV to 10 keV. The interaction process is understood in term s of the dynamical screening of the moving charge. With molecular part icles dissociation is observed. There are three possible pathways for dissociation, i.e. charge exchange, electronic excitation and rovibrat ional excitation. Evidence for all three processes is found experiment ally, however, in most cases rather indirectly by comparison with the results of model calculations. With atomic species capture into excite d states of the projectile is observed. Optical spectroscopy of the ex cited states shows large circular polarization, which depends on the m agnetization of the surface. The ''magnetic'' effect will be discussed in relation to the previous topics.