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 reported. The surface work function was varied by the exposure to cesium atoms. The electron energy spectra are interpreted in terms of various inter- 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 capture 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 states manifest themselves by their decay via Auger deexcitation and autodetachment, respectively. We observe one additional rather sharp feature which we tentatively attribute to the decay of the metastable negative ion state N-(2s(2)2p41D). For N2+ besides Auger capture into the N2 ground state also Auger deexcitation of excited N2 molecules (B; a3,1PI(g)) to the ground state seems to contribute to the spectra (below 0.2 ML). With increasing Cs coverage higher excited (Rydberg) states, in particular N2* E3SIGMA(g)+, become populated manifesting themselves by a variety of Auger deexcitation processes. For Cs coverages larger 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 Feshbach resonance N2-* E2SIGMA(g)+ (parent state N2* E).