Resonant charge transfer on the nanoscale:: studying doublet states of adsorbates by surface-enhanced Raman scattering

This paper summarizes a series of results where the main role of the charge-transfer (CT) mechanism in the surface-enhanced Raman scattering (SERS) of aromatic molecules is demonstrated. This mechanism consists on a photoinduced CT process between nanostructures of the metallic surface and the adsorbed molecules, giving rise to the transient formation of a radical anion of the adsorbate. A general methodology to detect the CT process in SERS is described. It is demonstrated that the SERS features are determined by the differences between the electronic properties of the neutral and the anionic molecular species. On the basis of these results, we propose to use SERS as a tool to characterize such doublet states. Copyright (c) 2005 John Wiley & Sons, Ltd.