Temperature Dependence of the Chlorine Pure Quadrupole Resonance Frequency in Molecular Crystals

Abstract

The Cl³⁵ pure quadrupole resonance frequency has been observed in polycrystalline CH₂Cl₂, CHCl₃, CCl₄, (CH₃)₃CCl, and CH₃CCl₃ at temperatures of 77°K and above. In all cases, the resonance frequency decreases at higher temperatures, in qualitative agreement with Bayer's theory for the torsional motions of the molecules. However, a quantitative comparison of the theory with experiment, including Livingston's results at 4 and 20°K, reveals significant discrepancies which are discussed and attributed mainly to the decrease in torsional frequencies at higher temperatures. The resonance was found to ``fade out'' at temperatures below the transition points in those solids, CCl₄, (CH₃)₃CCl, and CH₃CCl₃, where internal or molecular reorientations are known to occur. In the other compounds the resonance was observable up to the melting point. The origin of this phenomenon is discussed briefly.