Adduct formation of OH radicals and consecutive reactions of the adducts with NOx and OX

The formation of the adducts of OH with benzene, toluene and phenol and consecutive reactions of the adducts with No, NO2 and O2 are investigated in the temperature range from 300 to 350 K employing the flash photolysis/resonance fluorescence technique in Ar at 133 mbar. Observation of biexponential decays of OH over at least 2 orders of magnitude in the presence of the aromatics enables us to distinguish the three reaction channels in overlapping temperature ranges: abstraction of H by OH, addition of OH and unimolecular decomposition of the adduct. The reactions of the adducts with NO are observed to be negligible in all cases in contrast to previous data on benzene-OH values of approximately 3 x 10 high minus 11 cbm s high minus 1 are obtained for the rate constants of the reactions of the adducts with NO2, almost independent of reactant and temperature. Preliminary determinations of the adduct reactivities against benzene OH and toluene OH indicate that this path predominates under tropospheric conditions. The results for O2 are confirmed by direct observations of the adduct benzene-OH by the cw UV-laser longpath absorption technique.