Ion–ion–solvent interactions in solution. Part 4.—Raman spectra of aqueous solutions of some nitrates with monovalent cations

Abstract

The profile of the band due to the symmetric stretching of the nitrate ion in the Raman spectra of solutions of NH₄NO₃, Me₄N·NO₃, LiNO₃, KNO₃ and RbNO₃ has been component analysed. For the cations NH⁺₄ and Me₄N⁺ only one component was present. The bandwidth indicates that the ammonium ion causes enhanced dephasing while the tetramethylammonium ion produces essentially no perturbation. Solutions of LiNO₃ gave evidence of four concentration-dependent species identified as aquated ions, solvent-separated ion pairs, contact ion pairs and ion aggregates. Solutions of KNO₃ and RbNO₃ gave evidence of three species identified as aquated ions, ion pairs and ion aggregates. It was not possible to distinguish between contact ion pairs and solvent-separated ion pairs. Association quotients calculated for LiNO₃ solutions were K₁(1 mol dm^–3)= 1.34 dm³ mol^–1 and K₂(6 mol dm^–3)= 1.5, for KNO₃ solutions K(1 mol dm^–3)= 2.0 dm³ mol^–1 and for RbNO₃ solutions K(1 mol dm^–3)= 1.0 dm³ mol^–1.