Knowledge Bank

The adsorbed molecule whose Raman spectrum has been most thoroughly studied is pyridine on Using secondary ion mass spectroscopy, we have been able to show that the silver surface are atomically quite clean, except for the adsorbed pyridine. The case of pyridine adsorbed on Ag is of interest because of the anomalously high intensity of some of its Raman lines. In comparison with the intensity of the same vibrations in liquid pyridine, the intensity is enhanced by a factor of $104$. Several theories of this enhancement have been analyzed, and we have concluded that the enhancement is in fact a demonstration of the resonance Raman effect in which the surface plasmons mix with molecular electronic states so as to form a \emph{continuum} of intermediate states for the scattering. Implication of the surface plasma states requires a particular dependence of the Raman intensity on the frequency of the exciting radiation. Studies of this frequency dependence using a cw dye laser will be reported.