Electron emission in low-energy grazing collisions of CO + ions with W(110) partially covered by cesium atoms

Abstract

Electron energy spectra from slow CO + ions (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 clean W(110) and up to a Cs coverage of 0.2 ML (in terms of one completed adlayer at room temperature) an unique identification of the electronic transition processes could not be made on the basis of the electron spectra. Some observations indicate however that, besides direct Auger capture into the CO ground state, also Auger deexcitation of excited CO molecules (a 3Π) to the CO ground state and autodetachment of the CO − X 2Π shape resonance contribute to the spectra. With increasing Cs coverage excited states up to c 3Π become populated manifesting themselves by a variety of Auger deexcitation processes. For Cs coverages larger than 0.6 monolayers the resonant capture of an electron from the surface by CO b,B 3,1Σ + leads to the formation of the Feshbach resonance CO −* B 2Σ +. Again the formation of the resonance is detected by its decay via autodetachment.