Vibrational Relaxation in the Solid NaNO3–NaClO4, NaNO3–NaNO2, and Na2CO3–Na2SO4 Binary Systems

Abstract

Molecular relaxation processes in the solid binary systems NaNO₃–NaClO₄, Na₂CO₃–Na₂SO₄, and NaNO₃–NaNO₂ have been studied by Raman spectroscopy. It has been shown that the relaxation time of the ν₁(A) vibrational mode of the NO₃^- and CO₃^2- anions in the binary systems is shorter than that in individual (nitrate or carbonate) crystals. The increase in the relaxation rate can be accounted for by an additional mechanism for the relaxation of excited vibrational states of the anions in the binary systems. The mechanism involves the excitation of vibrations in a different anion (ClO₄^-, SO₄^2- or NO₂^-) and the “generation” of a lattice phonon. This relaxation mechanism is possible when the difference in frequency between the vibrational modes involved corresponds to a region with a sufficiently high density of states in the phonon spectrum.