The gas-phase reaction between O3 and HO radical: a theoretical study.

We report a theoretical study on the reaction of ozone with hydroxyl radical, which is important in the chemistry of the atmosphere and in particular participates in stratospheric ozone destruction. The reaction is a complex process that involves, in the first stage, a pre-reactive hydrogen-bonded complex (C1), which is formed previous to two transition states (TS1 and TS2) involving the addition of the hydroxyl radical to ozone, and leads to the formation of HO4 polyoxide radical before the release of the products HO2 and O2. The reaction is computed to be exothermic by 42.72 kcal mol(-1), which compares quite well with the experimental estimate, and the energy barriers of TS1 and TS2 with respect to C1 are computed to be 1.80 and 2.26 kcal mol(-1) at 0 K. A kinetic study based on the variational transition state theory (VTST) predicts a rate constant, at 298 K, of 7.37 x 10(-14) cm3 molecule(-1) s(-1), compared to the experimentally recommended value of 7.25 x 10(-14) cm3 molecule(-1) s(-1).