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

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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.