Raman study of rotational motion and vibrational dephasing dynamics of NO3-in molten nitrates

Abstract

The Raman spectra of the symmetric stretching v 1(A′1) mode of NO3 - ions have been measured in a series of molten nitrates, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, AgNO3, TlNO3, at a temperature 10–20 K above each melting point. Temperature dependence of the Raman spectrum was also measured in molten NaNO3. Reorientation of the symmetry axis of an nitrate ion is represented by the inertial motion of an associated ion cluster for short times and by rotational diffusion for longer times. One observes a point of inflection between two types of rotational motion at 0·2–0·5 ps. The speeds of inertial rotation and rotational diffusion decrease in the order, CsNO3, RbNO3, KNO3, NaNO3, TlNO3, LiNO3, AgNO3. The ratio of the effective moment of inertia obtained from moment analysis to the theoretical moment of inertia for a free NO3 - ion, I/I 0, increases in the same order, from 2·0 for CsNO3 to 20 for AgNO3. The vibrational correlation functions are analysed on the basis of a model of simultaneous homogeneous and inho...