Raman Spectral Studies of the Effects of Electrolytes on Water

Photoelectric Raman spectra of water at temperatures from 2° to 94°C have been obtained for the spectral region of about 0–4000 cm—1. Comparisons of these spectra, with Raman spectra of bromide and chloride solutions, indicate that certain intensities, which are increased by lowering the temperature of water, are also increased by electrolyte addition. Such intensity increases of Raman bands of the bromide and chloride solutions appear to be related to the ordering of water and ions. Other Raman bands of water, for which intensity increases occur with lowering of temperature, decrease in intensity with electrolyte addition. Those effects apparently are related to O–H···O bonds. The intensities of various bands studied, e.g., the librational bands, were observed to increase linearly with electrolyte concentration. In addition, marked intensity increases with increasing anionic size, i.e., Br—>Cl—, were observed, but the effects of the cations, while similar with respect to increasing size, appear to be relatively small. The linear intensity increases have been explained in terms of the concentration of ordered water-electrolyte units. The size effects have been considered in terms of the polarities of the bonds of those units.