Raman spectroscopic study of vibrational and rotational relaxation of the NO-3ion in molten binary systems (Li-K)NO3and (Na-K)NO3

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Abstract
Polarized and depolarized Raman scattering spectra for the totally symmetric stretching v 1(A′ 1) mode of the NO- 3 ion in the molten binary systems (Li-K)NO3 and (Na-K)NO3 have been measured. The spectra were Fourier-transformed to obtain the vibrational and rotational autocorrelation functions G v(t) and G R(t), respectively. Plots of the vibrational relaxation time against the mole fraction of the smaller cation show a negative deviation from additivity in the whole concentration region for both systems. The deviation is larger for (Li-K)NO3 than for the (Na-K)NO3 system. On the other hand, the rotational relaxation time shows positive deviations in similar plots. In particular, the rotational relaxation rate is considerably reduced on adding a small amount of LiNO3 into pure KNO3 melt. This shows that the strong coordination of a Li+ ion to several NO- 3 ions in the bulky mixtures rich in K+ ions appreciably restricts the rotational motion of the NO- 3 ions.