ELECTRON-EMISSION IN LOW-ENERGY GRAZING COLLISIONS OF N+ AND N(2)+ WITH W(110) PARTIALLY COVERED BY CS ATOMS

Electron energy spectra from slow nitrogen ions N+ and N2+ (50 and 500 eV) colliding under grazing incidence with W(110) surfaces are report ed. The surface work function was varied by the exposure to cesium ato ms. The electron energy spectra are interpreted in terms of various in ter- and intra-atomic Auger processes: For N+ Auger capture dominates up to a Cs coverage of about 0.2 ML (in terms of a completed monolayer (ML) at room temperature). For larger Cs coverages the resonant captu re of one or two electrons from the surface leads to the formation of core excited states of the neutralized projectile (beyond 0.3 ML) and of the Feshbach resonance N- (2s(2)2p(2)3s2) (beyond 0.5 ML). These s tates manifest themselves by their decay via Auger deexcitation and au todetachment, respectively. We observe one additional rather sharp fea ture which we tentatively attribute to the decay of the metastable neg ative ion state N-(2s(2)2p41D). For N2+ besides Auger capture into the N2 ground state also Auger deexcitation of excited N2 molecules (B; a 3,1PI(g)) to the ground state seems to contribute to the spectra (belo w 0.2 ML). With increasing Cs coverage higher excited (Rydberg) states , in particular N2 E3SIGMA(g)+, become populated manifesting themselv es by a variety of Auger deexcitation processes. For Cs coverages larg er than 0.6 ML the resonant capture of an electron from the surface by the Rydberg state N2 E3SIGMA(G)+ leads to the formation of the Feshba ch resonance N2- E2SIGMA(g)+ (parent state N2* E).