HYDROGEN ADSORPTION ON THE PT(111)(ROOT-3X-ROOT-5)R30-DEGREES-SN SURFACE ALLOY STUDIED BY HIGH-RESOLUTION CORE-LEVEL PHOTOELECTRON-SPECTROSCOPY

Investigation of the clean and atomic hydrogen covered Pt(111)(root 3 x root 3)R30 degrees-Sn surface alloy has been carried out using high resolution core level photoelectron spectroscopy, The Pt 4(7/2) spectr um recorded from the clean surface alloy shows a single surface peak s hifted - 0.25 eV relative to the bulk. Its interpretation by means of a thermodynamical model using Born-Haber cycles confirms the surface a lloy model. Adsorption of H does not change the line shape of the Sn 4 d core level while a new surface component shifted by 0.59 eV compared to the bulk peak appears in the Pt 4(7/2) spectrum. These results are discussed in the light of the thermodynamical calculations, H atoms a re believed to bind only to Pt atoms, and their adsorption site seems to be influenced by the tin present in the surface layer.