Raman and nuclear quadrupole resonance studies of the phase transition in pentachlorophenol

Abstract

Raman and nqr spectra of pentachlorophenol (PCP) have been recorded at temperatures above and below the transition at 62 + 2 °C. The complete loss of structure in the Raman external mode region and the disappearance of the 35Cl nuclear quadrupole resonances above the transition temperature indicate a disordered structure for the high temperature phase. Super-cooling is observed in nqr and Raman spectra when the sample is cooled through the transition temperature. No evidence for any new crystal phase is observed on cooling the sample to liquid nitrogen temperature. Eleven of the 12 external modes predicted from the reported crystal structure of PCP have been observed in the Raman spectrum at 77 K.