Magnetic resonance line shapes in solids. III. Methyl group tunneling in low temperature glasses

Abstract
NMR line shapes are reported for the protons in CH3CD2OD, CH3CD2Cl, CH3CD2Br, and CH3CD2I dissolved in perchloropropene glass at liquid helium temperature. Spectra were also observed for the solutions containing CH3CD2Br and CH3CD2I up to 120°K. All of the low temperature spectra are anomalous in shape and appear to result from superimposed spectra for methyl groups having different rotational barriers. An analysis is presented, based on the tunneling calculation of Apaydin and Clough, which yields two rotational barrier heights for each compound.