The resonance Raman (RR) and surface-enhanced resonance Raman (SERRS) spectra of M(PAN)2 complexes (M = Cd and Hg, PAN(-) = 1-(2-pyridylazo)-2-naphtholate) are reported and assigned, and the nature of the adsorbed species are determined. Vibrational assignments are supported by ab initio calculations at the B3-LYP/LanL2DZ level. There is clear evidence for chemisorption of these complexes on the silver surface, which gives rise to substantial alteration of the Raman spectrum. Comparison of the variation of Raman intensities with excitation wavelength for the RR and SERRS spectra indicates that there is a modification of electronic structure upon adsorption. Alterations in the Raman spectrum upon adsorption were successfully interpreted by ab initio calculations of the interaction of M(PAN)(2) complexes with surface silver atoms binding through the azo group alpha-nitrogen atoms.