An NMR Study of Molecular Reorientation in Solid Hexafluorobenzene (C6F6).
ILLINOIS UNIV URBANA NOYES CHEMICAL LAB
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Continuous wave and pulsed NMR studies were carried out on solid hexafluorobenzene C6F6 from 270 to 77K. The temperature dependence of the second moment exhibits two regions of motional narrowing, and that of the spin-lattice relaxation time shows minima at 142.5 and 260K. The spin-lattice relaxation in the rotating frame has a minimum at 172K and decreases toward a second minimum at low temperature. Although the line shape is asymetric in the entire temperature range, it differs between 100 and 145K from that at higher and lower temperatures. This intermediate region line shape is interpreted as a superposition of two components from motionally inequivalent hexafluorobenzene molecules. The second moment and relaxation time data are consistent with a model in which two different sets of C6F6 molecules reorient around their sixfold axis at different frequencies. Using BPP expressions, we obtain from our T1 and T1 rho data the following parameters for the low and high temperature motions. Author
- Physical Chemistry