ELECTRON-EMISSION IN LOW-ENERGY GRAZING COLLISIONS OF O+ GROUND (S-4) AND EXCITED-STATE ((2)D-(2)P IONS WITH ALKALATED W(110) SURFACES

Electron energy spectra have been measured for slow collisions (50 eV) of ground (4S) and excited state (2D;2P) O+ ions with W(110) surfaces under grazing incidence. The surface work function is varied by the exposure to alkali atoms (Na, K, Cs). In all cases electron emission is caused by various inter- and intra-atomic Auger processes. For clean W(110) and alkali coverages up to 0.2 monolayers (ML) (in terms of adsorbed layers at room temperature) only electron emission due to Auger capture is seen. With increasing alkali coverage Auger processes involving core excited atomic states (above 0.2 ML) and Feshbach resonances (above 0.55 ML) produced by the resonant transfer of one or two electrons to the projectile, respectively, dominate. For excited O+ ions we see also Auger processes in which the respective core excited states and Feshbach resonances do not decay to multiplet states of the neutral ground state configuration, but rather to lower core excited states. These processes require a rearrangement of the core state of the parent ion.