Difference in the Nonlinearity of Absorption in Natural and Synthetic Coals

It is established that on an increase in the super high frequency (SHF) radiation power for powder anthracite, a more rapid increase in the amplitude of the EPR line is observed in comparison to the case of linear absorption, whereas for carbon obtained by deposition of the products of pyrolysis of deuterobenzene (C{sub 6}D{sub 6}) on the surface of {gamma}-Al{sub 2}O{sub 3} there occurs saturation of absorption. At an air pressure of about 10{sup -3} mm Hg, saturation of resonance absorption is observed in both samples. The linear effects observed can be understood within the framework of the formalism of a three-level scheme possible in the case of the triplet ground state of the paramagnetic centers of powder anthracite.