Enhanced Raman characterization of adsorbed water at the electrochemical double layer on silver

Surface enhanced Raman scattering (SERS) from molecular water adsorbed on silver in an aqueous electrolyte is reported. The SERS active water is most probably associated with active sites on the metal which are stabilized by the double layer structure. The line shapes of the primary vibrations associated with the O-H stretch and the H-O-H bend are strong functions of the applied voltage, the electrolyte pH, and the bulk concentration of cations. At least two types of adsorbed water are observed. These data directly demonstrate that the structure of the first layer of water is significantly influenced by interaction with adjacent layers.