AN NMR INVESTIGATION OF THE DYNAMICS OF A METHYL-GROUP WITH TUNNELINGFREQUENCY 3.4 MHZ

The ground state tunneling frequency (nu(t) = 3.39 MHz) of the methyl groups in 2,5-dimethyl-1,3,4-thiadiazole has been measured using low f ield NMR-spectroscopy. Using a variety of rapid field cycling NMR tech niques the temperature dependence of nu(t) and the correlation time fo r incoherent reorientation tau(c) have also been measured. These have enabled the dynamics of the methyl groups to be studied from the quant um regime into the classical regime. These dynamics can be well descri bed with a purely threefold barrier of V/K(B) = 1175 K.