Structure of the D phase. II

Abstract Results are presented of a Fourier analysis of quantitative X-ray diffraction data obtained from a D phase single crystal, the structure of which has previously been shown to possess primitive cubic symmetry. The Fourier analysis method determines the distribution of electron density in the crystallographic unit cell from the intensities and phases of the Bragg reflections. Diffraction data provide no information on the phase factors, and the Fourier method is therefore practical only when the structure is centrosymmetric, as is shown to be the case for the D phase, since the phase factors are then either 0 or π. It is shown that there are essentially only four physically reasonable solutions for the electron density distribution. The physical interpretation of these models is discussed in terms of molecular packing in the unit cell.