Quantum mechanical tunneling in NMR: Effects of a potential barrier having sixfold symmetry on the spectrum of a methyl group

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Abstract
The Apaydin and Clough model of quantum tunneling rotation for a methyl group in a threefold symmetric hindering potential has been extended to potentials having sixfold symmetry. The spectra predicted by this extension have been generated for representative single crystal and powder patterns and the results compared with those of the threefold model. It is shown how misinterpretation of spectra which appear to fit the threefold tunneling description is possible, but significant differences occur only in a very limited range of tunneling frequencies which correspond to rather unrealistically high sixfold barrier heights. Some experiments are suggested which could possibly lead to experimental verification of the predicted effects directly in the NMR spectrum.