A conclusive study on the SERS band of pyridine occurring at about 1025 cm(-1) was performed by a density functional theory (DFT) approach, by considering the ligand molecules bound to silver adclusters. The existence of (Ag-3)(+2) surface active-sites, ascertained in Ag/SiO2 colloids as metal adclusters stabilised by the interaction with the silica nanoparticles, was confirmed by DFT calculations, which satisfactorily account for the experimental findings. (c) 2007 Elsevier B.V. All rights reserved.