Variation of the Near-Infrared Spectrum of Water from Dissolved Salts

摘要

In order to investigate the effect of dissolution of salts on the hydrogen-bonded network in liquid water, near-infrared absorption spectra of aqueous solutions of 16 salts, containing Na+ as common cation, were measured in the region where the first overtone of the -OH stretching mode of water is observed. Although the spectral variations of water resulting from dissolution of a salt is dependent on the kind of salt, principal component analysis of the observed spectra revealed that all spectral variations for the 16 salts were almost reproducible with only three components. The first component corresponds to the average of the observed spectra, while the other two components are responsible for the variations. The second component, which almost coincides with the component of the spectral variation of water from changes in temperature, was found to explain mainly the spectral changes by salts that destroy the hydrogen-bonded network. On the other hand, the third component, which includes the spectral changes at a lower wavenumber region than the second component, was found to mainly explain the spectral variation from the salts that expand the hydrogen-bonded network. These results suggest that observed spectral variations are not due to direct interaction between ions and water molecules, but due to the change of the hydrogen-bonded network because all variations produced by these 16 salts can be explained by only two components. The results suggest also that the mechanisms of destruction and expansion of the hydrogen-bonded network by the anions may be different.