We have investigated the adsorption of CO and CO2 on epitaxially grown Cr2O3(111) by means of EELS. LEED, ARUPS, NEXAFS and XPS. CO is found to adsorb on the oxide surface in an ordered (√3 × √3)R30° structure with the molecular axis oriented approximately parallel to the surface. CO2 on the other hand reacts with the chromium oxide to form a surface carbonate. Adsorption of CO, respectively reaction of CO2 only takes place on a clean, freshly flashed oxide surface. Preadsorption of oxygen leads to a surface which is rather inert to adsorption, likely due to electronic or steric reasons.
Near-edge X-ray absorption spectroscopy with linearly polarized synchrotron radiation has been applied to study the orientation of the helically shaped polyaromatic hydrocarbon P-heptahelicene (C 30 H 12 ) on a Ni(100) surface under ultrahigh vacuum (UHV) conditions. By measuring the polarization dependence of the C1s f π* transitions the local adsorption geometry was determined. Between the helical axis of the molecule and the surface plane an angle of 43 ( 5°was observed for a saturated monolayer.
The adsorption of benzene on Rh(lll) was investigated by using low-energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS).Under very good vacuum conditions we found a (\/l9 x \/l9)R23.4°pure benzene adsorption structure which could be converted to the c(2-3 x 4)rect and (3 x 3) structures by admission of CO. The adsorption symmetry, the possible adsorption sites, the orientation of the benzene molecules, and the molecular interaction in the adsorbate layer were investigated with ARUPS. The structure exhibits a work function change of Ae(i> = -1.47 eV, indicating one of the highest benzene densities on Rh(l 11) observed so far. A considerable dispersion of the 2aig-derived band of the adsorbate layer was observed.
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