Low-temperature resonance Raman scattering from iodide adsorbed on nanostructured silver surfaces

An overtone progression was observed in Raman scattering spectra from iodide-modified, electrochemically roughened silver surfaces at low temperatures. Spectral intensities of the bands were found to vary with the degree of surface roughening, whereas vibrational frequencies remained highly conserved. Both surface-enhanced and resonance scattering phenomena contribute to observed band intensities when excited in the spectral region between 406 and 415 nm. It is suggested that the progression originates from I-2-like species that are formed on small silver clusters at low temperatures under irradiation. This complex can be viewed as a supermolecule in which the electronic resonance is determined by the size of the cluster and I-I stretch represents a normal mode of the molecule.