Effect of Underpotentially Deposited Lead on the Surface-Enhanced Raman Scattering of Interfacial Water at Silver Electrode Surfaces

Abstract

The influence of underpotentially deposited Pb monolayers and submonolayers on the surface enhanced Raman scattering (SERS) of interfacial H2O at roughened Ag electrodes in aqueous chloride and bromide solutions is presented. With laser excitation at 5145 Å, the SERS intensity of the ν(OH) vibration of interfacial H2O at 3495 cm-1 and 3505 cm-1 in aqueous chloride and bromide, respectively, decreases as the first monolayer of Pb is deposited. The rate of the decrease is essentially independent of the nature of the supporting electrolyte anion and is significantly different than the rate of decrease of the ν(Ag-X) (X=Cl-, Br-) vibrations in these media. The presence of interfacial H2O at all coverages of UPD Pb precludes interpretation of these results strictly in terms of a decrease in adsorbate surface coverage. The results are interpreted as a combination of changes in electromagnetic enhancement resulting from alteration of the surface optical properties of the electrode in the presence of UPD Pb and decreased efficiency of photoassisted charge transfer resulting from alteration of the Fermi level at microscopic surface active sites in the presence of UPD Pb.