ESR of radicals in γ-irradiated mono and polycyclic olefin-I Cyclopentadiene: identification of a new radical species

In addition to cyclopentenyl radicals, the γ-irradiation of solid cyclopentadiene at 77°K results in the formation of polymeric radicals whose ESR h.f. structure has been isolated by progressive thermal annealing of glassy samples. Ultra-violet irradiation experiments suggest that the polymeric radicals have an ionic origin. Experimental evidence is also given regarding the absence of cyclopentenyl radicals arising from hydrogen atom addition to the double bonds. A reaction mechanism is proposed.