KINETICS AND MECHANISMS OF THE GAS-PHASE REACTIONS OF THE NO3 RADICAL WITH AROMATIC-COMPOUNDS

The kinetics and nitrated products of the gas-phase reactions of the NO3 radical with methoxybenzene, 1,2-, 1,3-, and 1,4-dimethoxybenzene, dibenzofuran and dibenzo-p-dioxin have been investigated at 297 +/-2 K and in the presence of one atmosphere of air. A relative rate method was used for the kinetic measurements. No reactions of methoxybenzene or dibenzofuran with the NO3 radical were observed. The dimethoxybenzenes were observed to react by H-atom abstraction and NO3 radical addition to the aromatic ring, while dibenzo-p-dioxin reacted by NO3 radical addition to the aromatic rings. For these compounds, the NO3 radical addition pathways were observed to be reversible. At the NO2 concentrations employed, the NO3-aromatic adducts reacted with NO2 and the observed rate constants increased with increasing NO2 concentration. However, for dibenzo-p-dioxin the observed rate constant became independent of the NO2 concentration for concentrations greater-than-or-equal-to 4.8 x 10(13) molecule cm-3, and under these conditions the rate constant of 6.8 x 10(-14) cm3 molecule-1 s-1 was taken to be that for addition of the NO3 radical to the aromatic rings. The proposed NO3 radical reaction mechanisms are discussed. (C) 1994 John Wiley & Sons, Inc.