Atmospheric Chemistry of the Phenoxy Radical, C_6H_5O(·): UV Spectrum and Kinetics of Its Reaction with NO, NO_2, and O_2

摘要

Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C_6H_5O(·) radicals. Pulse radiolysis experiments gave σ(C_6H_5O(·))_(235 nm) = (3.82 ± 0.48) * 10~(-17) cm~2 molecule~(-1), k(C_6H_5O(·) + NO) = (1.88 ± 0.16) * 10~(-12), and k(C_6H_5O(·) + NO_2) = 2.08 ± 0.15 * 10~(-12) cm~3 molecule~(-1) s~(-1) at 296 K in 1000 mbar of SF_6 diluent. No discernible reaction of C_6H_5O(·) radicals with O_2 was observed in smog chamber experiments, and we derive an upper limit of k(C_6H_5O(·) + O_2) < 5 * 10~(-21) cm~3 molecule~(-1) s~(-1) at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NO_x. Density functional calculations and gas chromatography-mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C_6H_5O(·) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C_6H_5OH) = (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 cm~3 molecule~(-1) s~(-1). A reaction between molecular chlorine and C_6H_5OH 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(Cl_2 + C_6H_5OH) ≤ 1.9 * 10~(-20) cm~3 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.