The Ordered Phase of p-Chloronitrobenzene Studied by Raman Spectroscopy

Abstract

p-Chloronitrobenzene exhibit an order-disorder phase transition at 282, K. The high temperature disordered phase has P2₁/c symmetry with two molecules per unit cell. A statistically centrosymmetric array results from the superposition of molecules occupying regular lattice sites but facing randomly opposite directions. The ordered low temperature phase structure could not be resolved yet. In the present work, Raman spectroscopy measurements were carried out as a function of temperature in the range 5, K--300, K in ordered and disordered phases of p-chloronitrobenzene. Symmetry information of the ordered unknown phase was obtained. A comparison of experimental results with Raman spectra of p-dihalobenzenes and p-dinitrobenzene has been carried out and possible molecular arrangements are discussed through lattice dynamics calculations.