Nuclear quadrupole resonance of Cl35 nuclei in glassy solution of chlorobenzene in pyridine

Abstract

Pulsed nuclear quadrupole resonance (NQR) measurements of Cl35 nuclei were performed on 43.5 mol % chlorobenzene solution in pyridine (a) in glassy state (Tg=131 K) after quenching in liquid nitrogen and (b) in crystalline precipitate under slow cooling starting from liquid phase. In both cases the NQR line shape, obtained by the fast Fourier transform (FFT) method, consisted of a structure of two peaks, interpreted as contributions of two nonequivalent nucleus35 sites. A theoretical model is proposed for the line-shape analysis and the best-fit parameters yield excellent agreement with experimental spectra. It is suggested that the nonequivalent sites consist of nearly parallel and antiparallel alignment of chlorobenzene and pyridine molecules and that the line-broadening mechanism is due to a random distribution of angular displacements from these positions. Our data are in agreement with Goldstein studies of molecular-relaxation processes related to the changes observed on physical properties of amorphous materials at Tg. © 1990 The American Physical Society.