STRUCTURES OF SOLID DEUTERIUM BROMIDE AND DEUTERIUM IODIDE

The structures of the three phases of DBr and DI were determined using neutron powder profile techniques. The highest temperature phases are cubic, Fm3m, with the deuteriums in twelvefold disordered positions about the halo-gens. The intermediate temperature phases are orthorhombic, Cmca, with the deuteriums in twofold disordered positions about the halogens in the mirror planes. In the lowest temperature phase of DBr, molecular ordering results in zigzag chains of molecules in the mirror planes of an orthorhombic structure with space group Cmc2(1). Molecular ordering appears in a different way in DI giving distorted diamonds (almost squares), rather than chains, and the rotational sense within the diamonds differs from one plane to the next. DI molecules are parallel or perpendicular to each other but the molecules point 6.27-degrees away from the lines joining the iodines. The structure is triclinic, with space group P1BAR.