Factor analysis of the attenuated total reflection (ATR) absorbance spectra of aqueous saline solutions has shown that these spectra are linear combinations of two eigenspectra: pure water and salt-solvated water. This paper outlines the general equations needed to formalize these experimental results. In the case of binary salts in aqueous solutions, the equations allow interpolation and extrapolation from one concentration to another. The accuracy of the calculation method was adequately verified on aqueous solutions of KCl. The equations made it possible to calculate the ATR absorbance spectrum of a "pure" KCl-solvated water. The latter, which contains no ordinary water, enabled us to determine that solvated water forms clusters made up of a pair of ions with five molecules of water. The same results were obtained with NaCl aqueous solutions.
Jean-Joseph Max and Camille Chapados, "Interpolation and Extrapolation of Infrared Spectra of Binary Ionic Aqueous Solutions," Appl. Spectrosc. 53, 1601-1609 (1999)