EPR of Matrix Isolated Methyl Radicals

High-resolution EPR spectra of CH3 radicals have been observed in Ar, Kr, Ne and CO matrices in the temperature range 1.6-4.2 K. These spectra manifested an anisotropy of both A-tensor and g-tensor. It is shown that the experimental spectrum can be simulated as a spectrum of a powder sample with axially symmetric g and A tensors. Having compared the spectra in various matrices as well as studied samples of both pure matrices and mixed matrices, we found a significant contribution of the radical-matrix interaction to the anisotropy. The contribution of the radical rotation at helium temperatures to the CH3 spectrum shape and the role it plays in the spectrum averaging are also discussed.