Raman spectral studies of ionic motion and ionic interaction in aqueous nitrate solutions

Abstract

The Raman spectra of the totally symmetric ν1(A 1′) mode of an NO3 - ion have been recorded in aqueous LiNO3, NaNO3, KNO3 and NH4NO3 solutions at various concentrations. The vibrational and rotational correlation functions have been calculated from the Fourier transform of the Raman profiles. Reorientation of the symmetry axis of an NO3 - ion in the aqueous solutions may be represented by the inertial motion for short times (t ≲ 0·15 ps, jump angle 17°), and by the rotational diffusion for longer times (t ≳ 0·3 ps). An effective moment of inertia for short times has been found to be I ⊥ = 20 × 10-39 g cm2, which suggests, as compared with the free NO3 - value I ⊥ 0 = 6 × 10-39 g cm2, some association with the surrounding water molecules or cations. The mean-square torque acting on an NO3 - ion from the moment analysis has been found to increase linearly with nitrate concentration. The torque on an NO3 - ion in concentrated nitrate solutions is predominantly from other ions, while the contribution from an ...