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 a bout the halo-gens. The intermediate temperature phases are orthorhomb ic, Cmca, with the deuteriums in twofold disordered positions about th e halogens in the mirror planes. In the lowest temperature phase of DB r, molecular ordering results in zigzag chains of molecules in the mir ror planes of an orthorhombic structure with space group Cmc2(1). Mole cular ordering appears in a different way in DI giving distorted diamo nds (almost squares), rather than chains, and the rotational sense wit hin the diamonds differs from one plane to the next. DI molecules are parallel or perpendicular to each other but the molecules point 6.27-d egrees away from the lines joining the iodines. The structure is tricl inic, with space group P1BAR.