CL-35 NQR STUDY OF THIOUREA-CCL4 AND THIOUREA-CCL3BR INCLUSION-COMPOUNDS

The Cl-35 nuclear quadrupole resonance (NQR) spectrum of the (thiourea)(3)-CCl4 inclusion compound has been determined at several temperatures in the range 5-20 K. The ratio of intensities of the two resonances was found to be 1:1, indicating that the tetrahedral CCl4 molecule sites in the trigonal thiourea channel with the molecular and site 2-fold axes coinciding. NQR frequency-swept spin-echo measurements of the (thiourea)(3)- CCl3Br inclusion compound reveal broad resonances at 40.995 and 40.690 MHz at 9.9 K, with a 1:2 ratio of intensities. The similar to 300-kHz separation and the temperature dependence of the resonance frequencies are the same as that observed in the thiourea-CCl4 compound, indicating that the two compounds are isomorphic at low temperatures. Cl-35 NQR relaxation times T-1 have been measured over the temperature range 4.3-25 K in the thiourea-CCl4 inclusion compound. These measurements indicate that above 18 K jump reorientation of the CCl4 molecules is the dominant relaxation mechanism, with an observed activation energy of 3.8 kJ mol(-1). T-1 has also been measured for the thiourea-CCl3Br compound over the temperature range 6-29 K. Above 21 K, jump reorientation of the CCl4Br molecules determines T-1.