THE AB-INITIO CRYSTAL-STRUCTURE DETERMINATION OF PERDEUTERODIMETHYLACETYLENE BY HIGH-RESOLUTION NEUTRON POWDER DIFFRACTION

The low-temperature crystal structure of dimethylacetylene-d(6) (2-butyne-d(6), CD3-C=C-CD3) has been solved ab initio from high-resolution neutron powder diffraction data. The structure is monoclinic, space group C2/m, with two molecules per unit cell. At 5 K, the cell dimensions are a = 7.15889 (4), b = 6.45529 (2), c = 4.07818 (9) Angstrom and beta = 101.0535 (5)degrees; V = 184.97 Angstrom(3). The powder diffraction pattern for the material exhibits hkl-dependent line broadening, apparently as a result of stacking faults intrinsic to the structure. Novel analysis techniques have been used to model line broadening and enable accurate structural parameters to be obtained.