VALENCE-LEVEL PHOTOEMISSION SPECTROSCOPY AND PHOTON-STIMULATED ION DESORPTION STUDIES OF CH3CL ADSORBED ON AL(111) SURFACE USING SYNCHROTRON-RADIATION

The interaction of CH3Cl adsorbed on Al(111) surface at similar to 90 K has been investigated by means of valence-level photoemission spectr oscopy (PES), work function change and photon-stimulated ion desorptio n (PSID) using synchrotron radiation. The one-to-one correspondence be tween the gas-phase and the condensed-phase CH3Cl PES spectra suggests that the molecules are molecularly adsorbed without decomposition. Ad sorption of CH3Cl leads to a decrease in work function of Al(111) (Del ta phi similar to-0.6 eV at a monolayer), indicating a dipole pointing away from the substrate and Cl is in direct contact with the metal. I n the H+ PSID spectra, three weak thresholds are observed, at similar to 9.6, similar to 13.9 and similar to 16.5 eV, and a major threshold appears at similar to 18.9 eV. CH3+ PSID spectra show a weak threshold at similar to 13.2 eV and two major thresholds near 9.0 and 16.7 eV. The desorption threshold below 18 eV may be due primarily to the singl e-hole excitation or Rydberg transition, whereas the ion desorption ab ove 18 eV may result predominantly from excitations of C 2s electron c orrelation states. (C) 1997 Elsevier Science B.V.