The temperature dependence of quantum mechanical tunneling effects in the nmr spectrum of a methyl group

NMR line shapes have been obtained for CH₃CD₂I in CD₃CD₂I from 4.2 to 127°K. At 4.2°K tunneling is evident, at 87°K neither tunneling nor classical rotation can be detected, and at 127°K there is rapid, thermally activated rotation. The apparent tunneling frequency is found to decrease with increasing temperature.