The Energetic Aspect of the Formation of Molecular Hydrogen During Gamma Irradiation of Liquid Cyclohexane

Molecular hydrogen, the basis of hydrogen energy, is formed in many physical and chemical processes, including the absorption of gamma-ray energy by liquid cyclohexane. From the point of view of energy consumption, the stages of gamma radiolytic formation of molecular hydrogen have not been quantified. By means of a new energy method, we analyzed the amounts of released molecular hydrogen during gamma irradiation of liquid cyclohexane in the absence and presence of small additives of bicyclic mono- and dienes RH (initial concentrations of C0(RH) ≈ 5 × 10−3 M/L), depending on the first ionization potentials of the components of solutions determined in the gas phase. Using the new energy method, four primary intermediates—radical anion, electronically excited molecule, radical cation, and superexcited molecule—of liquid cyclohexane gamma radiolysis were identified. Energy, mechanistic, and spin relationships and connections between these four cyclohexane intermediates were established. The experimental value of the adiabatic electron affinity of the cyclohexane molecule is −2.01 eV. The energy of formation of the superexcited cyclohexane molecule is 18 eV (gas phase). Using the energy method, it is shown that an increase in C0(RH) concentrations from 5 × 10−3 to 0.1 M/L leads to a change in the mechanism of RH consumption. Instead of RH activation, as a result of the single electron transfer reaction, RH polymerization begins, which is initiated by cyclohexyl radicals.