Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 21: Adsorption an Oberfl
ächen II

O 21.11: Vortrag

Dienstag, 25. März 2003, 17:30–17:45, HSZ/03

Adsorption and Reaction of Carbon Monoxide on Au(110)-(1x2) — •J. Michael Gottfried, Klaus J. Schmidt, and Klaus Christmann — Institut für Chemie der Freien Universität Berlin, D-14195 Berlin, Takustr. 3

The adsorption of carbon monoxide on a Au(110)-(1x2) surface was studied between 28 K and 300 K by means of TDS, UPS, NEXAFS, LEED, and work function measurements. Below 150 K, CO adsorbs non-dissociatively with high initial sticking probability (S₀ = 0.9 at 28 K). The initial isosteric heat of CO adsorption is 59 kJ/mol and decreases strongly with coverage, indicating weak chemisorption and marked repulsive CO-CO interactions. TD spectra show at least five desorption states corresponding to desorption energies between 38 and 9 kJ/mol. Accordingly, chemisorbed and physisorbed CO coexist in the first layer, a result that is corroborated by the coexistence of signals due to chemisorbed and physisorbed species in the UV photoemission spectra. CO adsorption has a complex influence on the surface potential 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 overlayer structures were observed in the whole coverage and temperature range. CO reacts vigorously with chemisorbed oxygen even below 100 K. The reaction rate reaches a maximum around 175 K and depends on the instantaneous, but also on the initial oxygen coverage. At 175 K and an O coverage of 0.45 ML, we found a CO/CO₂ conversion probability of 0.07.