NMR tunnelling effects in solid methyl fluoride

Proton and fluoride second moments and relaxation times have been measured as functions of temperature over the temperature range 131>T>7K. The results are dominated by the tunnelling of the CH3groups. The activation energy associated with the splitting between the ground torsional state and the first excited level was found to be 670 J mol-1. An estimate of the temperature dependence of the average tunnelling frequency is obtained from the results. The fluorine spins relax through the tunnelling system of the protons. In the rotating frame the very high tunnelling frequency ( approximately=44 GHz) gives rise to a serious discrepancy between calculated and experimental values since a common spin temperature is not attained.