Electron–electron double resonance study of magnetic energy transfer between trapped electrons and radicals in organic glasses: Relation between dipolar cross relaxation times and dipolar interaction distances

Electron–electron double resonance (ELDOR) has been used to measure cross-relaxation times between trapped electrons and trapped radicals produced by γ irradiation of 2-methyltetrahydrofuran and 3-methylhexane organic glasses. The cross-relaxation times are measured as a function of temperature, radiation dose, and the frequency difference Δf of the microwave frequencies used. The cross-relaxation times are nearly temperature independent and depend on Δf2 at doses where the spin concentrations approach uniformity; these features indicate the dominance of single step over multistep cross-relaxation processes. Equations have been derived to relate the dipolar cross-relaxation distance to the measured cross-relaxation times, and it is suggested that the cross-relaxation line shape is Lorentzian in magnetically dilute systems. Typical electron–radical correlation distances in these organic glasses are 10 Å.