Hydration structure of Na+ in concentrated aqueous solutions

X-Ray diffraction and Raman spectroscopic measurements have been carried ou t for aqueous 10mol% NaX (X = Cl, Br, ClO4, and NO3) solutions in order to determine the hydration structure of Na+ in concentrated aqueous solutions. Isotropic Raman spectra for NaX-H2O solutions exhibit a polarized peak cen tered at 183-187 cm(-1). The corresponding peak in the isotropic spectra fo r NaX-D2O solutions is shifted to the lower frequency side by ca. 10 cm(-1) , indicating that the peak can be assigned to the totally symmetric vibrati onal mode of hydrated Na+, Na+(H2O)(n). The least-squares fitting analysis was applied to the X-ray interference term observed for these solutions in order to discuss the hydration number of Na+ in concentrated aqueous soluti ons.