Electron spin relaxation times and internal motions of radicals in the solid state investigated by ENDOR and pulsed EPR

The angular dependent ENDOR spectra of the radical formed by gamma-irradiated single crystal of 4-methyl-2,6-di-t-butylphenol have been studied and the full hyperfine tensors of all the t-butyl and the ring protons have been obtained at T = 190 K. Pie found six different tensors for the t-butyl protons. This result shows that the t-butyl groups are slowly rotating on the ENDOR time scale, whereas each methyl group rotates fastly. The dynamical parameters of the motions have been determined by pulsed EPR experiments. The longitudinal relaxation and the phase memory times have been measured in the temperature range 130-290 K. Three different kinds of motions have been detected and the resulting values of the dynamical parameters have been compared with those obtained for the undamaged molecule by previous NMR studies.