Cidep after laser flash irradiation of benzil in 2-propanol. Electron spin polarization by the radical-triplet pair mechanism

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Abstract
Benzil ketyl radicals are generated by laser flash irradiation of benzil in 2-propanol at T = -50 °C and are observed by time-resolved ESR spectroscopy. Their electron spin polarization is found to consist of a fast and slowly rising emissive component. The fast component is due to polarized ketyl radicals formed by a two-photon process from an excited triplet state. The slow one is attributed to ketyl radicals which are generated by a slow photoreduction of benzil in its lowest triplet state. Their emissive polarization stems predominantly from the radical-triplet pair mechanism (RTPM). Rate constants of the relevant processes are determined.