Electron spin resonance studies of elementary processes in radiation- and photo-chemistry. Part 12.—Fluorinated carboxylic acids at cryogenic temperatures

Abstract

Some information concerning the mechanism of the radiolysis of perfluorinated carboxylic acids is presented from an examination of the e.s.r. spectra of radicals trapped in polycrystalline samples of the acids between 77 and 300 K. Three types of radicals have been identified in γ-irradiated samples of RCF₂COOH (R = F, CF₃, CF₃CF₂, C₆H₁₃, CF₂COOH, CF₂CF₂COOH). These are (1) parent radical anions RCF₂ĊOOH^–, (2) primary fluoralkyl radicals RĊF₂, and (3) secondary radicals RĊFCOOH. The radical anions lose F^– on thermal annealing to yield additional RĊFCOOH radicals, but when samples containing RCF₂ĊOOH^– are u.v.-irradiated at 77 K these species disappear without the appearance of any identifiable radical product, as do the corresponding species in non-fluorinated carboxylic acids. The RĊF₂ radicals are believed to originate from the cationic species formed in the initial ionization following proton transfer and elimination of CO₂.