Evidence for thermal quenching of methyl-group tunnelling rotation
- 7 October 1975
- journal article
- Published by IOP Publishing in Journal of Physics C: Solid State Physics
- Vol. 8 (19), 3115-3120
- https://doi.org/10.1088/0022-3719/8/19/011
Abstract
The proton spin-lattice relaxation time of 4-methyl-2,6-ditertiarybutylphenol is measured over the temperature range 12-50K where the relaxation is almost entirely due to rotation of the 4-methyl group. The object is to search for a feature predicted to occur when 2 pi nu t tau approximately , where nu t is the frequency of coherent tunnelling rotation and tau is the time constant for randomly occurring rotations. A feature of the expected kind is found near 33K leading to a value at this temperature of nu t=1.6+or-0.3 GHz. This is much less than the value of 9.4+or-0.1 GHz found by different methods in the range 4-9K. This result is in good quantitative agreement with the theoretical expectation that with increasing temperature, admixture of excited methyl-group torsional oscillator states leads to a reduction of nu t through a process of thermal averaging.Keywords
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