TILTED ADSORPTION OF BENZENE ON PT(110)1X2

The adsorption of benzene on the reconstructed Pt(110)1 x 2 surface wa s studied by temperature-programmed desorption (TPD), low-energy elect ron diffraction (LEED), angle-resolved UV photoemission (ARUPS) and ne ar-edge X-ray absorption spectroscopy (NEXAFS). At 100 K, benzene is m olecularly adsorbed on the Pt(110)1x2 surface. The saturated layer is disordered and corresponds to a coverage of similar to 0.28 ML. Anneal ing to 280 K leads to partial benzene desorption and to the formation of a well-ordered (4x2) layer (relative to the unreconstructed surface ) with a coverage of 0.25 ML. The missing ((2n+1)/4, 0) adsorbate LEED spots along [1 (1) over bar 0] indicate a glide plane in the adsorbat e structure and the existence of two molecules per unit cell. In this layer, benzene adsorbs with the molecular plane tilted by similar to 3 0 degrees in the [001] direction, as determined from ARUPS and NEXAFS. This geometry corresponds to a nearly flat adsorption on the (111) mi crofacets of the troughs of the reconstructed surface. The molecules h ave a well-defined azimuthal orientation with a C-H bond along the [1 (1) over bar 0] azimuth For dilute layers (theta=0.12 ML) and a disord ered layer with the same coverage as the ordered layer (theta=0.25 ML) , the molecules are also tilted into the troughs, a preferential azimu thal orientation is, however, not observed. (C) 1995 Elsevier Science B.V.