ON THE MECHANISM OF THE DECOMPOSITION OF ACIDIC O-3 SOLUTIONS, THERMALLY OR H2O2-INITIATED

Thermal or hydrogen peroxide initiated decomposition of acidic aqueous ozone is described as a chain process propagated by OH and O-2(-)/HO2 radicals. In the absence of H2O2 added, the chain is initiated by sur face-catalyzed formation of H2O2. Surface-dependent formation of H2O2 is experimentally verified. Since homogeneous radical-radical reaction s are much too inefficient to account for the termination, a heterogen eous chain termination is strongly suggested. Without addition of H2O2 no dependence of the decay on the surface-to-volume ratio could be ob served. However, on initial addition of H2O2 in amounts sufficient for homogeneous initiation to prevail, the rate of O-3 decay becomes prop ortional to the surface of the reaction vessel. These findings strongl y suggest that the decomposition of acidic aqueous O-3 is governed by initiation and termination processes occurring at the reaction-vessel surface, while its apparent appearance of a homogeneous solution-phase reaction results from the counteractive nature of these two processes .