AN ENDOR STUDY OF THE TEMPERATURE-DEPENDENCE OF METHYL TUNNELING

We have studied the motion of the methyl group in the free radical obt ained by gamma-irradiation of 4-methyl-2,6-di-t-butylphenol (MDBP). Th e ENDOR spectra have been measured in the temperature range 4.5 to 200 K. The positions of the methyl proton lines are temperature dependent . Their variation is accounted for by considering the transition from the quantum regime of motion of the methyl group at low temperature to the classic regime at higher temperature. This transition is found to occur in a temperature range narrower than that anticipated by Allen' s theory.