Vibrational Relaxation in LiNO3–LiClO4, Na2CO3–Na2SO4, and KNO3–KNO2 Solid Binary Systems

Abstract

Molecular relaxation in solid binary systems LiNO₃–LiClO₄, Na₂CO₃–Na₂SO₄, and KNO₃–KNO₂ was studied by Raman spectroscopy. The relaxation time of the ν₁(A) vibrations of the anion (NO₃⁻, CO₃²⁻) in the binary system was found to be smaller than in the individual crystal (nitrate or carbonate). The increase in the relaxation rate was explained by the presence of an additional relaxation mechanism of the vibrationally excited states of the anion in the binary system. This mechanism is associated with excitation of vibrations of another anion (ClO₄^-, SO₄^2-, NO₂^-) and generation of a lattice phonon. It was found that this relaxation mechanism takes place if the frequency difference of these vibrations corresponds to the region of sufficiently high density of states of the phonon spectrum.