Physisorbed, chemisorbed and dissociated O sub 2 on Pt(111) studied by different core level spectroscopy methods

For O sub 2 /Pt(111) we have found four different adsorption phases which are formed at different substrate temperatures. At approx25K the oxygen molecules physisorb on the surface. Two chemisorbed phases are observed at 90 and 135K, respectively. An atomic phase, characterized by a sharp (2x2) LEED...

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Bibliographic Details
Published in:Surface science 1995-11, Vol.342 (1-3), p.119-133
Main Authors: Puglia, C, Nilsson, A, Hernnas, B, Karis, O, Bennich, P, Martensson, N
Format: Article
Language:English
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Summary:For O sub 2 /Pt(111) we have found four different adsorption phases which are formed at different substrate temperatures. At approx25K the oxygen molecules physisorb on the surface. Two chemisorbed phases are observed at 90 and 135K, respectively. An atomic phase, characterized by a sharp (2x2) LEED pattern exists at a temperature above 150K. Different spectroscopic techniques have been used to characterize the four different adsorption states: XPS studies of adsorbate and surface core level shifts UPS, NEXAFS autoionization and Auger spectroscopy. We conclude that O adsorbs in two different molecular chemisorbed states which can be considered to be precursors for the thermally activated atomization process. The first of these molecular states is weakly chemisorbed at 90K. It is adsorbed in a hollow site with a saturation coverage of 0.23 (molecules per Pt surface atom). We have identified this phase as a superoxo-like configuration. The second phase is more strongly bonded to the platinum substrate. It is characterized by a longer and weaker molecular sigma bonding due to more charge transfer from the metallic substrate to the antibonding molecular 1 pi sub g orbitals than for the first chemisorbed phase. With a coverage of 0.15 the O molecules seem to be adsorbed in hollow or hollow-bridge sites. We have characterized this phase as a peroxo-like configuration of the O molecular. For atomic O on Pt we have found a coverage of 0.25 (O atoms per Pt surface atom) and a three-fold adsorption site in agreement with previous studies. We discuss the XAS results according to a model for the density of states induced by the hydridization of the 2p atomic orbitals with the 6sp states and 5d band of the metal.
ISSN:0039-6028