Structural investigation of water and aqueous solutions by Raman spectroscopy

Abstract

In the context of a long study of the dynamical properties of water and inorganic aqueous solutions using infrared (IR) and Raman spectroscopy, we present here recent results of the influence of salt concentration on the dynamics of water molecules. The main systems studied were salts of XnYm type (where X = Li+, Na+, K+, Rb+, Cs+, Mg2+, Zn2+ and Y = Cl-, ClO4-, NO3-, SO4-2). The whole spectrum reflects the molecular and ionic interactions between solvent molecules and solvent-solute and solute-solute molecules. Nevertheless, each spectral region supplies different information about these intermolecular interactions. The strong modifications in intensity and band profile undergone by the v(OH) band depends mainly on the nature of anions while cations have a weak influence. A picture of these different situations in a particular salt solution needs the support of a model of the dynamic structure of the water solvent. A discussion of the current state of the dynamical models of liquid water and new ideas on water dynamics are presented on the basis of the results obtained from the study of internal OH/OD vibrations of water in diluted mixtures of D2O/H2O. Finally, a comparative analysis of the influence on the dynamics of water molecules under the concentration of perchlorate and chloride salts of monovalent cations in water and isotopic D2O/H2O mixtures was undertaken using Raman spectroscopy.