On optically detected ESR spectra from radical cations of liquid hydrocarbon solvents

The optically detected electron spin resonance (OD ESR) method has been employed to study the origin of radical-cation ESR signals in some saturated hydrocarbons with small amounts of 2.5-diphenyloxazol or p-terphenyl under radiolysis. In cyclohexane, the ESR, signal with resolved hyperfine structure was ascribed to c-C₆H₁₀⁺/PPO^? radical-ion pairs produced from primary c-C₆H₁₂⁺/PPO^? ones by monomolecular decay, of cyclohexane radical cations to cyclohexene radical cations. Cis- and trans-decalin under radiolysis accumulate 9,10-octalin which captures solvent holes and form 9,10-octalin radical cations giving a resolved OD ESR spectrum. 9,10-octalin is present in non-irradiated commercial decalin as an impurity. The OD ESR technique has been shown to be very sensitive to some impurities in hydrocarbon solvents.