On the occurrence of the central line (similar to 1025 cm(-1)) in the SERSspectra of pyridine adsorbed on silver hydrosols

The occurrence of a central line at similar to 1025 cm(-1) between the surf ace-enhanced Raman scattering (SERS) bands of pyridine at 1008 and 1036 cm( -1) has been first detected in silver hydrosols. This band, which has no co unterpart in the Raman spectrum of the free ligand, is observed in acidic a queous suspension as corresponding to that observed in an electrochemical c ell and attributed to adsorption of pyridinium cation. When pyridine is ads orbed on an aged colloid in an alkaline medium two different species are de tected. A central band at about the same wave number occurs, attributable t o pyridine bound to silver ion cluster on the metal surface, oxidised by am bient air. (C) 2001 Elsevier Science B.V. All rights reserved.