AN IR STUDY OF THE HYDRATION OF CLO4-, NO3-, I-, BR-, CL-, AND SO42- ANIONS IN AQUEOUS-SOLUTION

The hydration of ClO4-, NO3-, I-, Br-, Cl-, and SO42- anions has been studied in aqueous solution. A double-difference IR spectroscopic method has been applied, whereby OD spectra of isotopically isolated HDO molecules in the hydration spheres of the anions are obtained after the contributions from H2O and HDO in the bulk are removed. Each anion is shown to interact with its neighboring water molecules, which gives rise to OD vibration bands with characteristic peak frequencies and bandwidths. The bandwidth is found to increase smoothly with increasing band position. The OD stretching intensity for hydrating water (HDO) molecules has been found to decrease linearly with band Position. Band positions have been converted to anion-water distances by means of correlation curves. These have been compared to available X-ray and neutron diffraction data on solutions and solid hydrates.