HIGH FRACTIONS OF NEGATIVE-IONS IN GRAZING SCATTERING OF FAST OXYGEN-ATOMS FROM A LIF(100) SURFACE

Oxygen atoms and ions with energies ranging from 2 to 100 keV are scat tered at grazing angles of incidence from a LiF(100) surface, We analy ze the charge states of the scattered beams as a function of the proje ctile energy. The most striking result of our study is the observation of negative ion fractions of up to about 70%. We interpret these larg e fractions of O- ions to capture in binary-type collisions of fluorin e 2p electrons from the target and the subsequent suppression of loss for these captured electrons due to the energy gap of the insulator.