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

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.