THE 2 SOLID-PHASES OF CHLORODIFLUOROMETHANE

The crystal structure of the two phases of chlorodifluoromethane (CHCl F2) were determined at 70 K and 10 K using Rietveld refinement of neut ron powder profiles. The upper phase is tetragonal P4(2)/n (C-4h(4)) w ith eight molecules in the unit cell occupying general positions. The lattice constants are a = 10 . 3711(1) Angstrom and c = 5 . 5915(2) An gstrom. The lower phase is monoclinic P112/n (C-2h(4)) with eight mole cules in the unit cell with dimensions a = 10 . 1106(2), b = 10 . 4830 (2), c = 5 . 5868(2) Angstrom and gamma = 90 . 319(2)degrees. The asym metric unit has two molecules in general positions. The phase transiti on is of a displacive type but there are no large changes in the molec ular positions or orientations at the transition.