Adduct Formation of OH Radicals with Benzene, Toluene, and Phenol and Consecutive Reactions of the Adducts with NO_<i>x</i> and O₂

Abstract

Abstract The formation of the adducts of OH with benzene, toluene and phenol and consecutive reactions of the adducts with NO, NO 2 and O 2 are investigated in the temperature range from ∼298–374 K employing the flash photolysis/resonance fluorescence technique in Ar at 133 mbar. Biexponential decays of OH can be observed over at least 2 orders of magnitude in the presence of the aromatics, and the three reaction channels: abstraction of H by OH, addition of OH and unimolecular decomposition of the adduct are distinguished in overlapping temperature ranges. Rate constants and preliminary Arrhenius parameters are obtained for these channels for benzene, toluene, and phenol. The reactions of the adducts with NO are very slow and can be neglected (&lt;10 −13 cm 3 s −1 ) in all three cases. Values of ∼3·10 −11 cm 3 s −1 are obtained for the rate constants of the reactions of the adducts with NO 2 , almost independent of reactant and temperature. Preliminary determinations of the adduct reactivities against O 2 ∼ 2 · 10 −16 (benzene‐OH) and ∼5 · 10 −16 cm 3 s −1 (toluene‐OH) near room temperature indicate that this path predominates under tropospheric conditions. The results for O 2 are confirmed by direct observations of the adduct benzene‐OH by the cw UV‐laser longpath absorption technique.