The crystal structure of phase III of chloroiodomethane-d2 was determi
ned at 13 K using Rietveld refinement of neutron powder profiles. The
space group is Pnma (D2h16) and there are four molecules in its orthor
hombic unit cell with dimensions a = 6.383(4) angstrom, b = 6.706(1) a
ngstrom and c = 8.867(4) angstrom. The molecules form a 'herringbone'
pattern in layers perpendicular to the b axis, similar to that in the
halogen and the hydrogen halides crystals.