ATMOSPHERIC CHEMISTRY OF THE PHENOXY RADICAL, C6H5O(CENTER-DOT) - UV SPECTRUM AND KINETICS OF ITS REACTION WITH NO, NO2, AND O-2

Pulse radiolysis and FT-IR smog chamber experiments were used to inves tigate the atmospheric fate of C6H5O(.) radicals. Pulse radiolysis exp eriments gave sigma(C6H5O())(235 nm) = (3.82 +/- 0.48) x 10(-17) cm(2) molecule(-1), k(C6H5O(.) + NO) = (1.88 +/- 0.16) x 10(-12), and k(C6H 5O(.) + NO2) = (2.08 +/- 0.15) x 10(-12) cm(3) molecule(-1) s(-1) at 2 96 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(.) radicals with O-2 was observed in smog chamber experiments, and we der ive an upper limit of k(C6H5O(.) + O-2) < 5 x 10(-21) cm(3) molecule(- 1) s(-1) at 296 K. These results imply that the atmospheric fate of ph enoxy radicals in urban air masses is reaction with NO,. Density funct ional calculations and gas chromatography-mass spectrometry are used t o identify 4-phenoxyphenol as the major product of the self-reaction o f C6H5O(.) radicals. As part of this study, relative rate techniques w ere used to measure rate constants for reaction of Cl atoms with pheno l [k(Cl + C6H5OH) = (1.93 +/- 0.36) x 10(-10)], several chlorophenols [k(Cl + 2-chlorophenol) = (7.32 +/- 1.30) x 10(-12), k(Cl + 3-chloroph enol) = (1.56 +/- 0.21) x 10(-10), and k(Cl + 4-chlorophenol) = (2.37 +/- 0.30) x 10(-10)], and benzoquinone [k(Cl + benzoquinone) = (1.94 /- 0.35) x 10(-10)], all in units of cm(3) molecule(-1) s(-1). A react ion between molecular chlorine and C6H5OH to produce 2- and 4-chloroph enol in yields of (28 +/- 3)% and (75 +/- 4)% was observed. This react ion is probably heterogeneous in nature, and an upper limit of k(Cl-2 + C6H5OH) less than or equal to 1.9 x 10(-20) cm(3) molecule(-1) s(-1) was established for the homogeneous component. These results are disc ussed with respect to the previous literature: data and to the atmosph eric chemistry of aromatic compounds.