STRUCTURE OF SOLID FLUOROFORM

The structure of fluoroform, CHF3, was determined at 4 . 2, 40 and 70 K using neutron powder profile analysis. There is only one phase with a monoclinic space group P2(1)/c. At the lowest temperature the lattic e parameters are: a = 4 . 7561(1) Angstrom, b = 6 . 6280(2) Angstrom, c = 8 . 5232(2) Angstrom beta = 122 . 02(2)degrees. Starting positions and orientations of the four molecules in the unit cell were determin ed to high accuracy using an energy minimization process with atom-ato m potentials. The structure is made up of weakly hydrogen bonded sheet s with adjacent sheets related by centres of symmetry.