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Transient dc conductivity is used to observe high-mobility ions in laser photolysis and pulse radiolysis of cyclohexane and decalins. While in decalins the scavenging of the dc conductivity signal from these ions by solutes is a pseudo-first-order reaction, in cyclohexane the behavior is more complex and is indicative of the involvement of two species. This bimodality is rationalized in terms of a dynamic equilibrium between the conformers of the solvent radical cation. A similar equilibrium between the isomer radical cations of decalin is needed to account for the results on photoinduced conductivity in the mixtures of cis-and trans-decalin. In both of these cases, the mechanism of the equilibrium is the reversible charge transfer.

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In several cycloalkanes, ionization of the solvent or photoexcitation of a solute radical cation results in the formation of rapidly hopping solvent holes. Here we report the temperature dependence of scavenging rate constants and conductivity signals (220 to 350 K) for the solvent holes in liquid cyclohexane, methylcyclohexane, and Decalins. Our results indicate that the hopping in Decalins and methylcyclohexane is thermally activated; the activation energies are of the same order as the energy of solvent reorganization. In cyclohexane, the hopping does not seem to be thermally activated. We discuss the hypothesis that the mobile solvent holes in cycloalkanes are small polarons migrating by phonon-assisted hopping.

The pulse radiolysis technique has been employed in studying charge-transfer reactions of anionic C2O4 -, and cationic C2O4 + species in supercritical carbon dioxide (scCO2) over a range of reduced densities ρr = 0.36−1.5 and at a reduced temperature of T r = 1.03. The absorption spectrum measured in the visible region with a maximum around 700 nm is assigned to the dimer cation C2O4 +. The pressure dependence of charge-transfer reactions was examined using dimethylaniline (DMA), benzoquinone (BQ), and oxygen as charge acceptors. The reaction rates of DMA with cations, and BQ with anions are at or near the diffusion-controlled limit. The rates decrease an order of magnitude with increase of pressure. The reaction of C2O4 + with oxygen is much slower with an almost constant rate over the pressure range examined. The measured rate constants of electron-transfer reactions are analyzed in terms of the diffusion constants of reactants in scCO2, and the dependence of measured and theoretical values on the bulk density is discussed.

In liquid cycloalkanes, single-photon excitation of solute radical cations leads to rapid transfer of a valence band electron and formation of a free solvent hole (“hole injection”). Quantum yields for this process upon 2.3 and 5 eV laser excitation of several aromatic radical cations in trans-decalin are reported and the photophysics of the hole injection in cycloalkane liquids is discussed.

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