ADSORPTION OF PYRIDINE ON NI(111) - A HIGH-RESOLUTION ELECTRON-ENERGY LOSS SPECTROSCOPY, ANGULAR-RESOLVED UV PHOTOEMISSION, AND X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY

High-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and angular-resolved UV photoemission are applied to the study of pyridine adsorbed on Ni(lll). Changes in the intensity of the in-plane versus out-of-plane vibrational modes show that an orientation phase transition occurs as a function of coverage at low temperature. The molecular plane is parallel to the surface at low coverages at 120 K, corresponding to π-bonded species. At higher coverages, the molecular plane tilts vertically with respect to the surface, indicating bonding through the N lone pair. This interpretation is consistent with ARUPS observations for pyridine exposures at 170 K. Heating results in desorption of weakly bound pyridine at 180 K and decomposition at 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. © 1990, American Chemical Society. All rights reserved.