ELECTRON-EMISSION IN LOW-ENERGY GRAZING COLLISIONS OF CO+ IONS WITH W(110) PARTIALLY COVERED BY CESIUM ATOMS

Electron energy spectra from slow CO+ ions (50 and 500 eV) colliding u nder 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-a tomic 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 ma de on the basis of the electron spectra. Some observations indicate ho wever that, besides direct Auger capture into the CO ground state, als o Auger deexcitation of excited CO molecules (a 3PI) to the CO ground state and autodetachment of the CO- X2 PI shape resonance contribute t o the spectra. With increasing Cs coverage excited states up to c 3PI become populated manifesting themselves by a variety of Auger deexcita tion processes. For Cs coverages larger than 0.6 monolayers the resona nt capture of an electron from the surface by CO b,B 3,1SIGMA+ leads t o the formation of the Feshbach resonance CO- B 2SIGMA+. Again the fo rmation of the resonance is detected by its decay via autodetachment.