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Atmospheric chemistry of the phenoxy radical, C6H5O(•): UV spectrum and kinetics of its reaction with NO, NO2, and O2

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  • J. Platz
  • Nielsen, Ole John
  • T. J. Wallington
  • J. C. Ball
  • M. D. Hurley
  • A. M. Straccia
  • W. F. Schneider
  • J. Sehested

Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C6H5O(•) radicals. Pulse radiolysis experiments gave σ(C6H5O(•))235 nm = (3.82 ± 0.48) × 10-17 cm2 molecule-1, k(C6H5O(•) + NO) = (1.88 ± 0.16) × 10-12, and k(C6H5O(•) + NO2) = (2.08 ± 0.15) × 10-12 cm3 molecule-1 s-1 at 296 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(•) radicals with O2 was observed in smog chamber experiments, and we derive an upper limit of k(C6H5O(•) + O2) < 5 × 10-21 cm3 molecule-1 s-1 at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NOx. Density functional calculations and gas chromatography-mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C6H5O(•) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C6H5OH) = (1.93 ± 0.36) × 10-10], several chlorophenols [k(Cl + 2-chlorophenol) = (7.32 ± 1.30) × 10-12, k(Cl + 3-chlorophenol) = (1.56 ± 0.21) × 10-10, and k(Cl + 4-chlorophenol) = (2.37 ± 0.30) × 10-10], and benzoquinone [k(Cl + benzoquinone) = (1.94 ± 0.35) × 10-10], all in units of cm3 molecule-1 s-1. A reaction between molecular chlorine and C6H5OH to produce 2- and 4-chlorophenol in yields of (28 ± 3)% and (75 ± 4)% was observed. This reaction is probably heterogeneous in nature, and an upper limit of k(Cl2 + C6H5OH) ≤ 1.9 × 10-20 cm3 molecule-1 s-1 was established for the homogeneous component. These results are discussed with respect to the previous literature data and to the atmospheric chemistry of aromatic compounds.

OriginalsprogEngelsk
TidsskriftJournal of Physical Chemistry A
Vol/bind102
Udgave nummer41
Sider (fra-til)7964-7974
Antal sider11
ISSN1089-5639
StatusUdgivet - 8 okt. 1998

ID: 225755061