The EPR spectra are complicated by the appearance of a large number of forbidden lines due to the presence of a chlorine quadrupole interaction similar in magnitude to the proton hyperfine coupling. Spectral assignment is not possible by considering the EPR spectra alone. Although ENDOR spectra are difficult to obtain, it is possible to obtain an ENDOR spectrum along one of the crystal axis that identifies the spectra as due to radical I. Furthermore, rather intense and highly resolved ELDOR spectra are obtained at - 60°C as a function of angle enabling the chlorine and proton magnetic hyperfine tensor components of the -CHCI fragment to be determined as - 15.4, - 8.3, + 45.6 MHz and - 26.5, - 52.5, - 80.0 MHz, respectively. The Q_n components of the chlorine quadrupole tensor is - 11.2 MHz.