The kinetics and mechanism of aqueous ozone decomposition in alkaline solution

Ozone decomposition in aqueous solution was studied by the stopped-flow met hod in the pH 10.4 - 13.2 range at 25 +/- 0.1 degreesC and I = 0.5 M NaClO4 . The absorbance change of the reaction mixture was monitored at the charac teristic absorbance maximum of ozone (260 nm) and ozonide ion radical (430 nm). A detailed radical type chain mechanism is proposed for the interpreta tion of the results. The kinetic role of previously ignored reaction steps of the chain carriers was tested by comparing experimental and simulated ki netic traces. The rate constants for the initiation and the kinetically dom inant reaction steps were estimated by simultaneous evaluation of the exper imental traces using a GEAR-algorithm-based non-linear least squares method . The proposed mechanism predicts the lifetime of ozone as well as the kine tics of the formation and subsequent decay of the ozonide ion radical (O-3( -)) reasonably well. Various factors affecting ozone stability and the deco mposition rate are discussed in detail. It is shown that some of the unique phenomena and irreproducibilities of the kinetic traces are related to hyd rogen peroxide formed during the preparation of ozone stock solution under acidic conditions. On the basis of the results, some of the discrepancies f ound in earlier literature can be resolved.