Adsorption of carbon monoxide on Au(110)-(1 x 2)

The adsorption of carbon monoxide on a gold (11 0)-(l x 2) surface was studied between 28 and 300 K by means of TDS, UPS, DeltaPhi, NEXAFS, and LEED. Below 150 K, CO adsorbs non-dissociatively with high initial sticking probability (S-0 = 0.9 at 28 K). The isosteric heat of CO adsorption is 59 kJ/mol for Theta(CO) --> 0 and decreases strongly with coverage, indicating weak chemisorption and substantial CO-CO repulsion, in agreements with TDS results. Thermal desorption spectra show at least five desorption states corresponding to desorption energies between 38 and 8 kJ/mol. According to TDS, chemisorbed and physisorbed CO coexist in the first layer, a result that is corroborated by UV photoemission spectra. CO adsorption has a complex influence on DeltaPhi and leads to a work function reduction of -0.95 eV at monolayer coverage. TDS and entropy measurements suggest that the state of chemisorbed CO at 160 K is best described by the model of a two-dimensional gas. No ordered CO overlayer structures were observed in the whole coverage and temperature range. (C) 2003 Elsevier Science B.V. All rights reserved.