Raman spectra of pyridine adsorbed on Ni(111)

We have measured the intensities of the 992 cm^?1 (ν₁) and 1032 cm^?1 (ν₁₂) lines in the Raman spectra of pyridine multilayers adsorbed on a Ni(111) surface, as a function of multilayer thickness. These experiments have been carried out in a standard ultra high vacuum chamber with Auger electron spectroscopy and mass spectroscopy capabilities. We find that the intensity of the 992 cm^?1 line decreases linearly with multilayer thickness down to ～ 5 layers. From these data and spectra of submonolayer quantities of Nitrobenzene on Ni(111) we predict an observable intensity for unenhanced spectra for monolayer amounts of pyridine on Ni(111). Attempts at observation of monolayer pyridine on this surface have been unsuccessful. We conclude that the scattering intensity of chemisorbed pyridine on Ni(111) is not enhanced and is likely less than would be predicted from the gas phase cross section.