Primary radical ions in irradiated carbonates†

This study focuses on primary radical ionic species created in liquid carbonates upon high-energy radiation. We studied the radiation-induced fluorescence intensity decays observed from solutions of luminophores in dimethyl, diethyl, ethylene, and propylene carbonates. Based on the effects of external magnetic and electric fields on the fluorescence decays on a timescale of 1–60 ns and quantum chemical calculations, we found that in all studied carbonates, solvent ionization was rapidly followed by the formation of comparatively long-lived positive charge and unpaired electron spin carriers. These carriers are complexes in which two carbonate molecules are oriented to each other by carbonyl groups, with the charge and spin density primarily distributed over these two CO groups. In the case of diethyl carbonate, the formation of such a complex occurs with a probability that depends on the conformation of ionized molecules and on the rate of parallel reaction of intramolecular proton transfer from the methyl or methylene groups to the carbonyl oxygen atom. In low-polarity carbonates, evidence for the existence of solvent radical anions with molecular mobility was found.