THE GEOMETRIC STRUCTURE OF THE SURFACE METHOXY SPECIES ON CU(111)

The adsorption geometry of the surface methoxy species (-OCH3) on Cu(111) has been determined quantitatively using scanned energy mode photoelectron diffraction in a two-step approach. First, using direct methods it was established that the fragment adsorbs via the oxygen atom at the ''fcc'' three-fold adsorption site. Subsequently, the structural parameters were refined by a search in multi-parameter space using diffraction spectra obtained in different emission geometries. The oxygen atom is found to be situated 1.32(+/-0.05) angstrom above the three nearest-neighbour copper atoms with the O-C axis essentially perpendicular to the surface. The O-C distance is 1.42(-0.03/+0.10) angstrom; a relaxation as well as a rumple of the outermost Cu layer occur.