Tilted adsorption of benzene on Pt(110)1x2

The adsorption of benzene on the reconstructed Pt(110)1 x 2 surface was studied by temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), angle-resolved UV photoemission (ARUPS) and near-edge X-ray absorption spectroscopy (NEXAFS). At 100 K, benzene is molecularly adsorbed on the Pt(110)1x2 surface. The saturated layer is disordered and corresponds to a coverage of similar to 0.28 ML. Annealing 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 adsorbate structure and the existence of two molecules per unit cell. In this layer, benzene adsorbs with the molecular plane tilted by similar to 30 degrees in the [001] direction, as determined from ARUPS and NEXAFS. This geometry corresponds to a nearly flat adsorption on the (111) microfacets of the troughs of the reconstructed surface. The molecules have 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 disordered layer with the same coverage as the ordered layer (theta=0.25 ML), the molecules are also tilted into the troughs, a preferential azimuthal orientation is, however, not observed. (C) 1995 Elsevier Science B.V.