Surface-enhanced Raman spectra of 2,2'-bipyrimidine adsorbed on silver sol

The surface-enhanced Raman spectrum of 2,2’-bipyrimidine adsorbed on silver sol has been obtained and analyzed by using a vibrational assignment previously determined for this azoaromatic molecule. Evidence was found for Ag-N bond formation with the silver substrate and a model is proposed for the adsorption on the basis of a very close similarity of the SER data with the normal Raman spectrum of a 1:l complex with AgNO3. Normal-mode analysis suggests a planar conformation for the adsorbed species, with the molecule perpendicular to the metal, bound through N atoms. Variation of relative intensities of Raman bands with different exciting lines is consistent with a charge-transfer contribution to the enhancement of the scattering cross section.