Quantitative determination of molecular adsorption structures using photoelectron diffraction: The methoxy species

Photoelectron diffraction in the scanned-energy mode is now an accepted method in surface structural analysis. Here we demonstrate its use in the determination of the local adsorption geometry of the methoxy species CH3O- on a Ni(111) surface. The bonding site of the O atom at an ''fcc'' hollow site directly above a Ni atom in the third layer is obtained from the experimental data using direct methods, and the exact Ni-O spacing and degree of local substrate distortion, together with the molecular orientation, are found by the use of multiple scattering simulations. A re-analysis of earlier data obtained for the same species on Cu(111) confirms the results of this earlier study and has allowed an evaluation of possible subtle differences in the adsorbate-induced substrate distortion despite the occupation of the same adsorption site and very similar O-metal nearest neighbour distances.