Surface-enhanced Raman scattering spectra of 2,4,6-trimethylpyridine recorded on silver at different electrode potentials have been analyzed on the basis of a charge transfer enhancement mechanism. The main feature of surface-enhanced Raman scattering is the enhancement of the band corresponding to the 8a mode at negative electrode potentials. This behavior can be explained by Franck-Condon factors related to a photoinduced electron transfer process between the metal and the adsorbate. The selective surface-enhanced Raman scattering enhancement is related to the differences between the ab initio equilibrium geometries of the electronic levels involved in the resonant mechanism, i.e., the ground states of the neutral adsorbate and the respective radical anion. (C) 2003 Elsevier B.V. All rights reserved.