Evidence for Ag cluster vibrations in enhanced Raman scattering from the Ag/electrolyte interface

Low-frequency vibrational features are observed in the enhanced Raman spectra from an electrochemically roughened Ag electrode. Evidence is found that these features are related to resonant Raman scattering from the internal vibrations of small Ag clusters stabilized on the surface. Comparison of the experimental data with the results of a simple normal mode calculation suggests that a possible identity for such clusters is pyramidal Ag⁺₄. These clusters may be responsible for some of the “chemical” factor in SERS from coadsorbed molecules.