STRUCTURAL STUDIES OF CYCLOHEXANE, C6D12, BY NEUTRON-DIFFRACTION .2. THE PLASTIC CRYSTAL PHASE

Neutron diffraction measurements have been made on the plastic crystal phase of C6D12 at temperatures of -10, -5 and 0-degrees-C. The results show a rapid attenuation of the intensity in the crystalline structure factor peaks as a function of Q such that the high Q-value pattern is identical with that of the liquid phase and determined entirely by the conformation of the molecule. Transformation of the data to a real-space representation gives an orientational average which can be directly compared with the spatial distribution of the disordered liquid phase. The general characteristics of the distribution cannot be interpreted by a model based on a free rotator phase and are more directly related to a disordered fcc lattice. Certain features indicate local orientational correlations between adjacent molecules.