Nuclear quadrupole resonance line shape study of the orientationally disordered phase of p-chloro nitrobenzene

Abstract

An experimental study of the nuclear quadrupole resonance (NQR) line shape of p-chloro nitrobenzene in the temperature range 77–150 K is reported. The molecules of p-ClC6H4NO2 in the solid phase are arranged following an orientationally disordered pattern. The experimental NQR spectra at several temperatures are unusually broad for a molecular crystal and show a structure of peaks. Our measurements suggested that the line broadening is due to a static distribution of disordered molecules. In order to explain the nontypical resonance frequency dispersion, a simulation of the NQR line shapes is carried on. The model for the simulated crystal assumes that each molecule is an electric dipole and that the crystal is a disordered binary alloy of dipoles having two possible orientations. By calculating the intermolecular contribution to the electric field gradient (EFG) at the resonant nuclei sites, we get the expected EFG distribution in the sample. The approach we propose here explicitly involves the symmetry of the lattice.