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Laboratory studies of atmospheric aqueous phase free radical chemistry: Kinetic and spectroscopic laboratory studies of reactions of NO3 and SO4- radicals with aromatic compounds

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Herrmann, H. , Exner, M. , Jacobi, H. W. , Raabe, G. , Reese, A. and Zellner, R. (1995): Laboratory studies of atmospheric aqueous phase free radical chemistry: Kinetic and spectroscopic laboratory studies of reactions of NO3 and SO4- radicals with aromatic compounds , Faraday discussions, 100 , pp. 129-153 .
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Abstract:

Recent results from kinetic and spectroscopic laboratory studies of reactions of free radicals such as NO3 and SO4- with aromaticcompounds in aqueous solution at T = 298 K are presented. Three different experimental approaches, (i) laser photolysis-visible long-pathlaser absorption, (ii) laser photolysis-UV long-path laser absorption and (iii) time-resolved broadband diode-array spectroscopy, havebeen used to investigate the kinetics of reactions of NO3 and SO4- with aromatics, as well as the formation of oxidation intermediates.For the reactions of NO3 with benzene (1), anisole (2), p-xylene (3), p-cresol (4), toluene (5), mesitylene (6) and 1,4-dimethoxybenzene(7), rate coefficients of k(1) = (4.0 +/- 0.6) x 10(8) 1 mol(-1) s(-1), k(2) = (1.0 +/- 0.4) x 10(9) 1 mol(-1) s(-1), k(3) (1.6 +/- 0.1) x10(9) 1 mol s(-1), k(2) = (1.0 +/- 0.4) x 10(9) mol(-1) 1 s(-1), k(3) = (1.6 +/- 0.1) x 10(9) 1 mol(-1) s(-1), k(4) = (8.4 +/- 2.3) x 10(8)1 mol s(-1) k(5) = (1.2 +/- 0.3) x 10(9) 1 mol(-1) s(-1), k(6) = (1.3 +/- 0.3) x 10(9) 1 mol(-1) s(-1) and k(7) = (1.0 +/- 0.3) x 10(9) 1mol(-1) s(-1) were obtained. For the corresponding reactions of SO4- with benzene (8), toluene (9), p-xylene (10), p-cresol (11) andmesitylene (12), rate coefficients of k(8) = (6.4 +/- 2.5) x 10(8) 1 mol(-1) s(-1), k(9) = (1.3 +/- 0.6) x 10(9) 1 mol(-1) s(-1), k(10) =(2.7 +/- 0.9) x 10(9) 1 mol(-1) s(-1)k(11) = (2.8 +/- 0.8) x 10(9) 1 mol(-1) s(-1) and k(12) = (1.3 +/- 0.4) x 10(9) 1 mol(-1) s(-1) weredetermined. Reactivity correlations for both radical species with the aromatic compounds are presented and potential applications of suchcorrelations are discussed. In addition, the effect of ionic strength in the reactions of NO3 with benzene and toluene has been investigated.Transient intermediates have been spectroscopically identified in the reactions of the sulfate radical anion in aerated as well as inoxygen-free solutions. The nature of these intermediates is discussed in view of the existing literature. Finally, possible impacts offree-radical reactions with aromatic compounds on the current understanding of chemical conversion processes within troposphericmultiphase systems are considered.

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