Ion-molecule reactions of primary radical cations in the liquid-phase radiolysis of n-alkanes: An EPR study

Radiation-chemical yields the liquid-phase radiolysis of C5–C12n-alkanes were measured using the spin trap technique. The yields of n-alkyl radicals depended only slightly on the chain length in C5–C9 alkanes and amounted up to 30% of the total yield of trapped radicals; they were inhibited by the addition of charge scavengers. An analysis of the experimental results together with data on radicals in irradiated crystalline alkanes and radical cations in freon matrices showed that n-alkyl radicals results from the ion-molecule reactions of primary radical cations, whereas the protonated ions RH2+ as products of these reactions are a source of sec-alkyl radicals. At least 60% of primary radical cations are consumed via these reaction pathways. A part of sec-alkyl radicals is due to gauche-conformers. The relative amount of primary alkyl radicals formed in the degradation of excited states and the subsequent charge neutralization processes should be insignificant.