Primary events in hydrocarbon radiolysis: real-time studies of radical-cation chemistry

Recent studies of the radiolysis of liquid alkanes by picosecond emission and absorption spectroscopy and by Fluorescence Detected Magnetic Resonance (FDMR) are discussed. These studies establish that the parent radical cations of smaller alkanes have short lifetimes (''less than''10 ns). Ion-molecule and fragmentation reactions of alkane radical cations exhibit surprising diversity. Cyclohexane and trans-decalin radical cation are the shortest-lived. Cyclohexane+. has a lifetime of ∼ 0.3 ns and also has a great propensity to transfer a proton, rather than a charge, to other additives. These observations are discussed in the context of past work on hydrocarbon radiolysis and recent measurements of G-values of solute excited states. An important conclusion is that such radical-cation reactions are quite important in any analysis of experiments designed to probe early events in hydrocarbon radiolysis where the method depends on the integrity of the solvent radical cation. Because geminate radical cation-electron recombination is typically faster than ion-molecule reactions of the radical cation, the effect of such radical cation reactions of final products is expected to be minor. (author)