Analysis of the Internal Rotation of the · CF2CONH2 Radical as Observed by ESR in Irradiated Trifluoroacetamide Single Crystals

The temperature-dependent ESR spectrum of the · CF2CONH2radical (found in x-irradiated single crystals of trifluoroacetamide) has been measured at both 9 and 35 GHz over the temperature range from 77 to 290°K. A model is proposed which explains the observed temperature dependence in terms of a torsional oscillatory motion about the C–C bond with a barrier height, V0=3100 cal. Nonadiabatic spin exchange is used to account for the doublet splitting of the central line at 77°K changing to a single sharp line at all angles at 290°K. The exchange rate is described by the empirical equation r−1=3.6 × 108 exp(−410 cal/RT).