Reaction of O(1D) with H2 and the Reactions of H and OH with Ozone

The reaction of O(1D) with H2 (and D2) has been studied by photolysis of O3–H2 and O3—D2 mixtures dissolved in liquid argon at 87°K. Quantum yields of O3 decomposition and product yields (as water) based on O3 decomposed were measured both with and without added O2 as a scavenger. O(1D) reacts with H2 with zero Ea and at a rate slightly less than the previously studied O(1D)—CH4 reaction. A major path is O(1D)+H2→H+OH. H atoms from this reaction can be scavenged by added_O2 by the reaction H+O2+M→HO2+M. Neither OH nor HO2 reacts with O3 under the conditions of these experiments. By contrast, H atoms not scavenged by O2 react with O3 in a manner which leads to chain decomposition of at_least 25 O3 molecules per H atom. The proposed chain is H+O3→OH*+O2,OH*+O3→H+2O2.The symbol OH* represents vibrationally excited OH, and therefore the process is an energy chain. If the proposed mechanism is correct, OH* must be produced in the reaction of H with O3 with essentially 100% efficiency in order to account for the observed chain lengths. Also, OH* reacts with O3 at least 103 faster than with H2 under the conditions of these experiments.