Structure of aqueous solutions: Infrared spectra of the water librational mode in solutions of monovalent halides

The variations of the infrared librational mode of water with concentration of added salt have been examined at 30°C for solutions of NH4F, NH4Cl, NH4Br, NH4I, LiCl, LiBr, NaCl, NaBr, NaI, KCl, KBr and KI. The data indicate that water in the primary hydration sheath can be distinguished from the remainder of the water and primary hydration numbers have been estimated. It is shown that in general the larger the ion the greater the change to the spectral band. The ammonium fluoride is shown to be unique in producing little disturbance of the water structure