FREE RADICAL FORMATION IN HYDROCARBON CRYSTALS BY GAMMA IRRADIATION . ELECTRON SPIIN RESONANCE SPECTRA OF SOME ALKYL RADICALS

Single crystals and polycrystalline samples of the n-alkanes, pentane, hexane, heptane, nonane, decane, and undecane, were prepared by a freezing technique. The crystals were irradiated at 77°K with 60Co γ rays to a dose of 3 Mrads. Electron spin resonance in the X band and Q band demonstrated that CH3-CH-CH2-R is the predominant radical species in all hydrocarbons except for undecane. The measured coupling constants found are the isotropic a1 = 25 ± 1 G (quartet), a2 = 33 ± 1 G (triplet), and the orientation dependent doublet splitting a3 = 12.5 -33 G. A complexity in the central region of the spectrum from undecane is thought to indicate the presence of additional alkyl radicals. Cleavage of the carbon chain is improbable. An irreversible decrease in line width with temperature has been explained in terms of a disappearance of the dipolar interaction between radicals some 30 Å apart. In single crystals indications of radical pair formation have been found.