Abstract
Radical cations derived from saturated hydrocarbons are highly reactive oxidizing species, and the rates of their bimolecular reactions are often determined by the frequency of diffusion collisions in solution. It is known that reactions of primary radical cations (holes) arising in cyclohexane, methylcyclohexane, and cis and trans -decalins on exposure to ionizing radiation can be 10 to 100 times faster than molecular diffusioncontrolled reactions [1, 2]. Investigations have shown that the high reaction rates in these cycloalkanes are due to the very high mobility of the primary holes of the solvent, which is caused by degenerate electron transfer between the radical cation and surrounding solvent molecules. No highly mobile holes have been observed in other cycloalkanes or in normal and branched alkanes [1, 2]. In this study, the methods of time-resolved magnetic field [3, 5] and electric field [4] effects in recombination fluorescence of geminate radical-ion pairs, developed in our previous works, were used to detect highly mobile solvent holes. Owing to the high time resolution ( ~1 ns), these methods provide the detection of highly mobile holes having shorter lifetimes than those detectable by the techniques used previously. For the formation mechanism of the magnetic field effect, it is significant that ionizing irradiation of alkane solutions produces geminate radical-ion pairs mainly in the singlet spin state. The singlet‐triplet transitions in the pairs induced by hyperfine coupling (HFC) and the differences in the radical g -factors or paramagnetic relaxation modulate the yields of the singlet-excited molecules resulting from recombination of radical ions. The time variation of the recombination fluorescence I ( t ) of the irradiated solutions can be written as follows:
Published Version
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