ADSORPTION OF HYDROGEN ON PT(100) AT LOW-TEMPERATURES

We have investigated the structure of the hydrogen-covered Pt(100) sur face by high-resolution helium diffraction and compared it with the cl ean one. At surface temperatures below 250 K hydrogen adsorption leads to characteristic changes in the surface structure, as observed also by other authors [1-5]. While this structure was previously denoted as ''(1 x 1)-like'', our He-diffraction patterns clearly show, that the reconstruction is not removed at temperatures below 250 K. The diffrac tion patterns of the hydrogen-covered surface are compared to those ob tained for the reconstructed Pt(100)-hex surface and the unreconstruct ed clean Pt(100)(1 X 1) surface (hydrogen coverage < 1%) The corrugati on functions for these three surfaces were obtained using the eikonal approximation. The modified surface corrugation of the ''(1 X 1)-like' ' structure is interpreted as a charge redistribution caused by the ad sorbed hydrogen on the surface.