Abstract
It is demonstrated unambiguously that a single methyl group can be responsible for two well resolved minima in the temperature dependence of its proton spin-lattice relaxation time. The analysis of seven infrared absorption bands verifies that these minima are due to (i) hindered threefold reorientation of the methyl group and (ii) transitions of the methyl group between its ground and first excited torsional state. The investigations were made on the isolated methyl group in p-tert-butyltoluene, which was found to have a threefold potential barrier hindering its reorientation of amplitude (4.13+or-0.07)kJ mole-1.