Theory of Critical-Fluctuation-Enhanced Raman Scattering by Phonons in NH4Br

The hypothesis due to Wang and Fleury that the Raman scattering from the ${56-\mathrm{c}\mathrm{m}}^{-1\mathrm{}}$ phonon in N${\mathrm{H}}_4$Br is enhanced by critical fluctuations in the neighborhood of the transition temperature is derived from a theory of Raman scattering from phonons in a system with partially disordered force constants, by making some reasonable assumptions about the behavior of the polarizability as a function of ammonium-ion orientation.