The orientation of pyridine on Pd(110): An angle-resolved photoemission study

Abstract

The orientation of pyridine on Pd(110) has been studied by angle-resolved UV photoelectron spectroscopy (ARUPS) with use of synchrotron radiation in conjunction with low-energy electron diffraction (LEED) and work function measurements. The pyridine molecules in the saturation adlayer are arranged into an ordered c(4×2) LEED structure. The strong anisotropies of photoemission into the [001] and [11̄0] azimuths suggest azimuthal orientation. Analysis of ARUPS in terms of polarization-dependent symmetry-derived selection rules provides strong support for a near-parallel η6 configuration, and a surface bonding via the aromatic π electron system. Experiments utilizing photoemission into the mirror planes of the (110) surface allow to specify the azimuthal orientation of the molecules, viz., with the N atom aligned along the [001] direction. In combination with the ordered LEED pattern a structure model for the pyridine adlayer is presented.