Relaxation of vibrationally excited states in solid “nitrate–nitrite” binary systems

Abstract

The processes of molecular relaxation in the solid NaNO₃–NaNO₂ and KNO₃–KNO₂ “nitrate–nitrite” binary systems have been investigated by Raman spectroscopy. The relaxation time of the vibration ν₁(A) of an NO^-₃ anion in the binary system is found to be shorter than that in individual nitrate. The increase in the relaxation rate is explained by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is related to the excitation of vibration of another anion (NO^-₂) and generation of a lattice phonon. It has been established that this relaxation mechanism is implemented provided that the difference between the frequencies of the aforementioned vibrations correspond to the range of sufficiently high density of states in the phonon spectrum.