Infra-red spectroscopic studies of aqueous systems. Part 2.—Fundamental infra-red spectrum of the ammonium ion in aqueous solutions and effect of anions on water absorptions

Abstract

The effect of concentration on the infra-red active vibrational frequencies of the ammonium ion in the range 4000–1100 cm^–1 has been studied in aqueous solutions of NH₄F, NH₄Cl, NH₄Br, NH₄I, NH₄ClO₄, NH₄NO₃, NaClO₄. The frequencies for the NH⁺₄ ion reach a constant value on dilution to [graphic omitted] 2 M, and with increasing concentration approach the values for the crystalline solids. The effect of the larger anions on the contour of the water absorption near 3420 cm^–1 and on the apparent relative intensity of the water band near 1640 cm^–1 are discussed.