Temperature Dependences of the Spectra of Aqueous Solutions of Alkali Metal Chlorides in the Mid-IR Range

Temperature dependences of the spectra of aqueous solutions of LiCl, KCl, RbCl, CsCl with concentrations of 3 M in the mid-IR range in the temperature range of 39 to 2 degrees C are studied. Average rate Delta v/Delta T of the temperature shift of the wavenumber of the maximum of absorption bands of valence (nu(1), 2 nu(2), nu(3)), composite nu(2) + nu(L), and deformation nu(2) vibrations of the water molecule for the studied solutions of alkali metal chlorides are obtained. Based on the observed patterns of the displacement of these absorption bands as the temperature changes, a conclusion is drawn regarding structural changes in these solutions. Values Delta v/Delta T for solutions with similar values of distilled water are compared, showing that there are differences between the structural variations in water and in the studied solutions as the temperature changes. The numerical values of the energy and the length of hydrogen bonds between water molecules are calculated with decreasing temperature for all studied solutions; the energy of hydrogen bonds rises as the temperature falls, while their length is reduced in all of the studied solutions.