The local adsorption geometry of benzene on Ni(110) at low coverage

Using scanned-energy mode photoelectron diffraction we have determined the local adsorption geometry of benzene adsorbed on Ni(110) at a coverage of approximately 0.1 monolayers. The molecule is found to adsorb with its molecular plane parallel to the surface, centred on a four-fold coordinated hollow site, with two opposite C-C bonds perpendicular to the close-packed [110] rows of surface nickel atoms and a C-Ni nearest-neighbour layer spacing of 1.81 +/- 0.02 Angstrom. The unusually high precision in the determination of the C-C distance in the benzene ring (1.45 +/- 0.03 Angstrom) if the molecule is assumed to retain its full gas-phase symmetry shows that there is a significant increase in this distance relative to the free molecule (1.39 Angstrom). (C) 2000 Elsevier Science B.V. All rights reserved.