The determination of the effective rotational potential in the plastic phase of C₂Cl₆from neutron Bragg scattering data

The effective rotational potential V(ω) in the plastic phase of C2Cl6 is computed from neutron diffraction Bragg data. The formalism used applies the Boltzmann factor exp (- βV(ω)) in order to describe the orientational pair distribution function of the smeared nuclear scattering density. A model potential calculated from atom-atom interactions in an (8 + 1) cluster of molecules reproduces the potential V exp(ω) determined from the experiment fairly well. From this we conclude that V exp(ω) is due to the time independent crystalline potential rather than due to the averaged random rotational torque. The lowest rotational barrier height is approximately 1000 K.