NEUTRON-DIFFRACTION STUDY OF 1,2,3-TRICHLOROBENZENE-D3

In order to explain the observed Cl-35-NQR anomaly of the title compou nd, a neutron diffraction study on single crystals was carried out at 295 K and 158 K. No significant structural changes concerning phase tr ansitions or molecular disorder between the two experiments were obser ved. The space group is P2(1)/c = C-2h(5) with 8 molecules per unit ce ll. The asymmetric unit contains 2 molecules. The cell parameters were deteriyiined to a = 1264(4) pm, b = 825 (2) pm, c = 1503 (3) pm, beta = 14.3(3)-degrees at 295 K and a = 1243(2) pm, b = 815(1) pm, c = 149 4(2) pm, beta = 114.3(1)-degrees at 158 K. The molecules show rigid-bo dy behaviour. No significant changes of the molecular geometry were ob served. A strong variation of the temperature factors as function of t he temperature was detected. An anharmonicity of the librational poten tial of the molecules was found by evaluation of the thermal parameter s as function of temperature. For verifying the existence of dynamic p rocesses which lead to a bleaching out of the Cl-35-NQR lines differen ce, Fourier syntheses were calculated. A reorientation or an order-dis order process as suggested by Cl-35-NQR spectroscopy above 230 K could not be confirmed within the error of the experiments. The degree of d euteration of the samples was determined by refinement of the occupati on factors of the deuterium sites.