How are hydrogen bonds perturbed in aqueous NaClO4 solutions depending on the concentration?: A near infrared study of water

We have performed spectroscopic measurements on the vibrational combination bands of OH-bending (nu(2)) and asymmetric OH-stretching (nu(3)) modes of water in aqueous NaClO4 solutions with an absorption spectrometer in the near infrared region. The concentration dependence of the spectral shape of the nu(2) + nu(3) band around the wavelength of 2 mum was investigated, where the NaClO4 concentration was varied by a factor of 200. The spectral shape depends significantly on the concentration of NaClO4 and the spectral width of the saturated aqueous solution becomes narrower to about half of that of pure water. The concentration dependence is analyzed from the viewpoint of water molecules with a different number of hydrogen bonds. The perturbation effect of ions on hydrogen bonds between water molecules is discussed.