Electronic absorption spectra of benzoyl radicals produced from benzoyl halides by irradiation with γ-rays in organic glass

Abstract

Benzoyl radicals, formed by dissociative electron attachment to substituted benzoyl bromides and iodide in γ-irradiated organic glasses at 77 K, were identified by optical absorption bands centred in the region 600–700 nm, although benzoyl chloride produced its radical anion by a non-dissociative process. Under visible light illumination, the absorption due to benzoyl radicals in a rigid matrix decreased owing to the cleavage of the bond between the phenyl ring and carbonyl carbon. The decay of benzoyl radicals under visible light illumination was faster than that of the alkyl-ĊO. This indicates that the conjugation of an electron between the phenyl ring and carbonyl group is not important; consequently, an unpaired electron may be localized mainly on the σ-orbital of the carbonyl group. Other optical spectral characteristics which should be caused by the localization of an unpaired electron on the σ-orbital of the carbonyl group are discussed.