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At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiation

Abstract

Formation yields of OH radicals were precisely determined in aqueous solutions of coumarin-3-carboxylic acid and ferrous sulfate (i.e., Fricke dosimeter) exposed to 253.7-nm radiation delivered from a continuous source. Quantum yield of OH radicals was determined as  0.08, i.e. roughly one of twelve photons efficiently absorbed in UV - illuminated solutions produces one OH radical. Energetically, a water molecule should undergo a correlated action of at least two 4.9-eV photons delivering enough energy for direct H-OH dissociation, i.e., 5.0-5.4 eV. We suggest a mechanism based on an interaction of two water molecules, both in long-living triplet states. An intermolecular transfer of excitation energy provides an amount of energy sufficient for the dissociation of one molecule into OH and H. In an aqueous solution of phospholipids, quantum yields of hydroperoxides formed under these irradiation conditions decrease with total effectively absorbed energy (i.e. a dose), similarly as the radiation chemical yields behave during an exposure to ionizing radiation, e.g., gamma rays from radionuclide sources. Under 253.7-nm irradiation, one OH radical causes a peroxidation of 34 phospholipid molecules. It implicates chain mechanism of the reaction.

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Publication details

The article was received on 28 Jul 2017, accepted on 09 Oct 2017 and first published on 10 Oct 2017


Article type: Paper
DOI: 10.1039/C7CP05125E
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiation

    K. Tomanová, M. Přeček, V. Múčka, L. Vysin, L. Juha and V. Čuba, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP05125E

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