A MOLECULAR-BEAM INVESTIGATION INTO THE DYNAMICS AND KINETICS OF DISSOCIATIVE O-2 ADSORPTION ON PT(100)-(1X1)

The dissociative chemisorption of oxygen on Pt{100}-(1X1) has been inv estigated using supersonic molecular beams with incident translational energies between 0.04 and 0.90 eV over the surface temperature range 300 to 380 K. The adsorption process on the Pt{100}-(1X1) surface is f ound to differ from that on the reconstructed Pt{100}-hex-R surface in both magnitude and mechanism. The initial dissociative sticking proba bility is >0.2 on the (1X1) surface for all beam energies and surface temperatures investigated, whereas on the reconstructed Pt{100}-hex-R surface, under corresponding conditions, the initial sticking probabil ity never exceeds 0.003. The initial sticking probability On the (1X1) surface at first decreases with increasing incident energy and then i ncreases as the incident energy exceeds 0.1 eV, in a manner typical of an adsorption process that is precursor mediated at low incident ener gies and direct at higher incident energies. Precursor-mediated adsorp tion at low energies is also indicated by scattering measurements and by the angular variation of the initial sticking probability. At high incident energies the angular variation of the initial sticking probab ility indicates that adsorption is an activated process. Sticking prob ability measurements as a function of coverage indicate no extrinsic p recursor involvement over the energy range studied; repulsive lateral interactions exist between adsorbed oxygen atoms. Thermal energy atom scattering measurements show an absence of island formation upon adsor ption, in contrast to adsorption on the hex-R face. (C) 1996 American Institute of Physics.