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REEVALUATION OF THE SPECTRAL AND KINETIC PROPERTIES OF HO 2 AND O 2 ‐ FREE RADICALS
Author(s) -
Bielski Be H. J.
Publication year - 1978
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1978.tb06986.x
Subject(s) - radiolysis , radical , chemistry , reaction rate constant , formate , analytical chemistry (journal) , aqueous solution , molar absorptivity , dissociation (chemistry) , kinetic energy , chemical reaction kinetics , kinetics , chemical kinetics , physics , chromatography , organic chemistry , quantum mechanics , optics , catalysis
— The spectra and molar absorbances of the HO 2 and O 2 ‐ free radicals have been redetermined in aqueous formate solutions by pulse and stopped‐flow radiolysis as well as by 60 Co gamma‐ray studies. The extinction coefficients at the corresponding maxima and 23°C are 225 = 1400 ± 80 M ‐1 cm ‐1 and 225 = 2350 ± 120 M ‐1 cm ‐1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO 2 and O 2 ‐ : K Ho2+HO2 = (8.60 ± 0.62) × 10 5 M ‐1 s ‐1 ; K Ho2+O2‐ = (1.02 ± 0.49) × 10 8 M ‐1 s ‐1 ; K Ho2+O2‐ < 0.35 M ‐1 s ‐1 . For the equilibrium HO 2 → O 2 ‐ + H + the dissociation constant is K Ho2 = (2.05 ± 0.39) × 10 ‐5 M or p K HO2 = 4.69 ± 0.08. G (O 2 ‐ ) has been evaluated as a function of formate concentration.