Direct ionization-driven observational approaches for radical cation formation in solution for pulse radiolysis

Abstract

Radical cations’ dynamics in early stage reactions in the ionizing radiation induced reaction is essential to understanding the whole reaction scheme. The observation of radical cations in tetrahydrofuran (THF) solutions was demonstrated for time-resolved measurements using pulse radiolysis. The designedly concentrated solutions enabled the observation of the direct ionization-driven radical cations. In THF, the transient absorption spectra of the biphenyl radical cations, which were generated through direct ionization of biphenyl under electron beam irradiation, were found to be associated with the biphenyl radical anions generated by the attachment of an excess electron to the biphenyl. Furthermore, when polystyrene (PS) was used as the solute in THF solutions, transient absorption spectra of the dimer radical cations containing solvated electrons of PS were observed. The findings, therefore, indicate that the time-resolution-based limitation on the radical cation-forming process observation, which was imposed by the diffusion-limited reactions of the solvent radical cations with the solute, could be overcome by employing direct ionization in THF. This method can be employed to study the reactivity of radical cations with solvents and the stability of radical cations in fluid media.