HREELS, ARUPS AND XPS OF PYRIDINE ON NI(110)

High-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and angular-resolved UV photoemission are applied to investigate the adsorption of pyridine on Ni(110). At low temperature, changes in the intensity of in-plane versus out-of-plane vibrational modes show a change in the surface orientation of the molecule as a function of coverage. The molecular plane is parallel to the surface at low coverages, indicating bonding through the pi molecular orbitals. At high coverages the molecular plane tilts toward normal with respect to the surface. This interpretation is consistent with ARUPS observations at normal emission. Heating results in desorption of weakly adsorbed pyridine at 180 K, with chemisorbed pyridine remaining in its low temperature orientation through room temperature. Decomposition occurs by 520 K, where the C-C and C-H stretching modes and the C-H deformation modes which are observed are uncharacteristic of molecular pyridine.