NEAR-INFRARED SPECTROSCOPIC STUDIES OF AQUEOUS-ELECTROLYTE SOLUTIONS

The near-infrared difference spectra of aqueous solutions of NaCl. KCl and Bu(4)NBr have been reported in the concentration range of 0.5 to 3.0 m at 22 +/- 1 degrees C. The combination band (nu(1),+ nu 2 + nu 3) of water has been mainly studied. Some measurements for the first overtone of -CH band in Bu(4)NUr solutions have also been presented. The combination water band is subjected to analysis by applying McCabe and Fisher method to yield the hydration spectra which can be resolved into two components for all the salt solutions studied except for Bu(4)NBr solutions. The low frequency component centered at 1200 nm is assigned to anion-water hydrogen bond, while the high frequency band at 1160 nm is assigned to non-hydrogen bonded water molecules in the hydration sphere of the cation. The hydration numbers for the salts have been calculated and compared to those obtained from other techniques. The results are explained in terms of ion-solvent interactions. The case of Bu(4)NBr appears to be anomalous and has been explained on the basis of its peculiar structure stabilization properties in aqueous solutions.