Temperature dependence of the Raman spectra of NaClO4 in relation to the 581 K phase transition

Abstract
The evolution of the internal and external modes in the Raman spectra of NaClO4 has been studied in the neighbourhood of the transition temperature, at 581 K. Large changes in the frequencies of the external modes with temperature have been observed. These changes can be explained in terms of a model based on the reorientation of the perchlorate ions.