Peculiarities of EPR spectra of methyl radicals in quench-condensed krypton films

Methyl radicals are trapped in the solid Kr film by simultaneous condensation of gaseous Kr and the products of a gas discharge in CH(4)-doped Kr on a low-temperature (4.2 K) substrate located at the center of the microwave cavity. The observed EPR spectrum is a superposition of broad-line and narrow-line series. At a low resonance microwave power, the latter series consists of four hyperfine components with nearly equal intensities and shows small axial anisotropy of both the g and A tensors. At a sufficiently high power the two central narrow lines split, so that the narrow-line series takes on the appearance recorded elsewhere for CH(3) in Ar at higher temperatures above 12 K. Simultaneously, the intensity of the two central broad lines increases dramatically, while the outer components become saturated. A possible explanation is discussed.