Triplet-State Electron Spin Resonance of an H-Atom-Methyl-Radical Complex in a Solid Matrix

The electron spin resonance of paramagnetic species produced by γ irradiation of solid methane at 4.2^∘{}K has been observed. In addition to the expected signals from individual H and CH₃ radicals, weaker signals from exchange-coupled H and CH₃ radicals were observed. The exchange interaction is isotropic, but there is an anisotropic dipole-dipole interaction between the aligned electron spin moments which gives rise to a splitting of 91 G. Analysis of this interaction indicates the separation of the coupled H and CH₃ to be 6.76 {}. The hyperfine splitting by the H is 255 G and that by each proton of the CH₃ group is 11.5 G, or one-half those for the isolated H and CH₃. These features are shown to be in agreement with theoretical predictions. Similar effects were observed for CH₄ irradiated in a krypton matrix at 4.2^∘{}K.