SERS STUDIES ON ELECTRODE ELECTROLYTE INTERFACIAL WATER .1. ION EFFECTS IN THE NEGATIVE POTENTIAL REGION/

Utilizing a special roughening procedure and a difference spectrum met hod, we have studied electrolyte ion effect on surface enhanced Raman scattering (SERS) of interfacial water molecules at silver electrodes, for the first time, in solutions free of (pseudo-) halide ions. The S ERS obtained from alkali sulfate or perchlorate solutions in the negat ive potential range (- 2.0 to - 1.3 V) reveals that the cation effect of water on SERS falls into two groups according to the O-H stretching frequencies: Cs+ and Li+ are in one group, while K+ and Na+ are in th e other. The formation of electrolyte ion pairs and localized hydrolys is of water molecules around the cation were used to interpret the res ults. By using a flow cell to replace the electrolyte under potential control, we found that the effect of the anion (e.g. SO42-, ClO4- and OH-) on the SERS of water is not negligible, even at very negative pot entials, which may be due to the formation of ion pairs at the electro chemical interface.