Raman spectra of electrolyte solutions in light and heavy water

Abstract

The Raman spectra of light water, heavy water and mixtures of these have been obtained, and vibrational frequency assignments have been made for H 2O, HDO, and D 2O. Changes in frequency, intensity and band width of the solvent bands have been determined for KF, KCl, KBr, KI and LiBr dissolved in H 2O-HDO mixtures at concentrations up to 6M. All of the salts except KF increased the stretching frequencies, while the bending frequency remained practically unchanged. The shape of the O-H stretching band was changed and the intensity was slightly increased by added salts, while the intensity of the bending band increased by as much as an order of magnitude. Band widths of both bands were generally decreased by dissolved salts. These effects increased monotonically with increasing concentration, and the influence of different anions was in the order F − < Cl − < Br − < I −, with the fluoride ion generally having an effect opposite to that of the others. No difference was found between the effects of LiBr and KBr. Changes in the spectrum similar to those found in salt solutions were noted when the temperature of the pure solvent was raised from 12° to 82°C. The change in shape of the O-H stretching band can be attributed to a Fermi resonance between ν 1 and 2ν 2. Other changes in the spectra are attributed to a combination of electrostatic interaction between ions and solvent dipoles and a decrease in hydrogen-bonding of the solvent.