SERS investigation of interfacial water at a silver electrode in acetonitrile solutions

Surface-enhanced Raman scattering from a silver electrode in solution of 0.1 M LiClO4 in acetonitrile has been analyzed as a function of applied potential. Three ν(O–H) bands associated with the interfacial water and two ν(O–H) bands associated with the OH− ion species were observed depending on the electrode potential. The band at 3487 cm−1 is favored at relatively positive potentials and assigned to H2O molecules interacting with the electrode surface via the oxygen atoms. Another band at 3586 cm−1 appears in a wider potential region and is assigned to the H2O molecules with one or both of the hydrogen atoms facing the electrode surface. Additionally, evidence for the possible surface ion pair, Li+OH−, which is closely associated with H2O molecules and the quasi-crystalline form of LiOH are also presented in this paper.