Electron spin resonance study of radiation-induced radicals in polycrystalline aromatic carboxylic acids containing a thioether group

Radicals and radical ions formed on γ-radiolysis of aromatic carboxylic acids containing a thioether group in the polycrystalline state at 77 K and on subsequent warming over the temperature range of 95-293 K were identified using the electron spin resonance technique. In all carboxylic acids studied, monomeric sulfur radical cations (X-S+-Y-COOH) and radical anions formed by an addition of an electron to the carboxyl group (X-S-Y-COOH)− were detected at 95 K. On further warming over the 150-293 K range various S-centered radicals (XS) and C-centered radicals were observed. The results are discussed in terms of the following competitive reaction pathways: fragmentation, decarboxylation, and deprotonation of the parental monomeric sulfur radical cations. Carbon dioxide was identified and quantified (G=0.2-3.5) in all carboxylic acids exposed to γ-radiation.