SPECTROSCOPIC INVESTIGATIONS OF THE STRUCTURE OF LIQUID WATER AND AQUEOUS-SOLUTIONS

IR spectroscopy is a powerful tool for investigating the structure of aqueous systems. Changes in vibrational frequencies and intensities of the absorption band provide information about the structure of the associated water molecules. The water molecule has C2v symmetry when the intermolecular interaction is symmetrical to both OH bonds as in 2:1 complexes. In this case the frequency difference of the two stretching vibrations ν3 and ν1 is nearly constant. If the intermolecular interaction is unsymmetric to the OH bonds as in 1:1 complexes the band separation of ν3 and ν1 increases markedly in relation to the increase of the unsymmetry. The IR overtone region is more suitable for the study of the structure of liquid water or aqueous solutions than the IR fundamental region. The reason is the higher intensity of the absorption bands of the free" OH vibration compared to the H-bonded OH groups. The ratio of the intensities is inverse in the fundamental region. Furthermore it is possible to measure quantitatively in the overtone region and there are no experimental difficulties. The results are estimations of the H-bonded and the free OH groups in different aqueous systems. © 1979."