| Chemical modification of Mo(100) surfaces by 1.0 - 1.5 monolayers of electronegative adatoms produces electronically deficient surface metal atoms as a result of charge transfer. Surface atom chemical states were measured by XPS. For Mo(100) surfaces modified by 1.0 monolayer of B, C, CO or O, the Mo oxidation number was linearly dependent on the adatom electronegativity. At oxygen coverages below one monolayer, a chemisorbed oxygen phase exists which produces a constant Mo oxidation number of 1.3. At higher coverages, a rapid increase in the Mo surface atom charge indicates the formation of a surface oxide layer.;Rapid pulsed laser heating of surfaces was used to examine molecular adsorption and desorption processes. Mass specific velocity distributions of CO and NO desorbed from Cu(100) were obtained by time-resolved quadrupole mass spectrometry. The resulting CO translational temperatures were dependent on the experimental variables which determine the integrated desorbed flux and on molecule-molecule collisions occurring above the surface on the desorption time scale. A variety of surface species resulting from the decomposition and reaction of NO on Cu(100) were observed. The leading edge of the 14 amu distribution is earlier than that observed for the possible parent molecules indicative of an atomic desorption or molecular decomposition process. Chemisorption of CO on Cu(100) is non-dissociative. Flight times corresponding to the leading edge of the 12 amu and 16 amu distributions are appropriate for atomic fragments of CO leaving the surface. Electron emission from the laser-irradiated surface was observed at light fluences comparable to those which can induce CO desorption. Adsorbate dissociation via interaction with these electrons is postulated to be the result of a surface-mediated process. (Abstract shortened with permission of author.).;The electron deficient Mo surfaces atoms are acidic sites for adsorption of gas phase Lewis bases. The adsorption of ethylene, propene, ammonia, dimethyl ether and 3,3,3-trifluoropropene on chemically modified Mo(100) surfaces and on MoO(,2) was investigated by XPS and UPS. The bonding modes of ethylene, propene and dimethyl ether were those which could be associated with a molecular charge transfer acid-base process. For 3,3,3-trifluoropropene, surface electron donation to unoccupied adsorbate levels was also observed. Adsorption on the oxide surface was initially molecular. |
