The photolysis of ozone by ultraviolet radiation. VI. Reactions of O( 1 D)

Abstract

Tho reactions of O( 1 D) with O 3 , and with O 2 , have been studied by means of two essentially different techniques. Relative quantum yields for ozone decomposition after photolysis by λ = 254 nm radiation were measured by following changes in optical absorption. Relative concentrations of ground state oxygen atoms were measured by means of a resonance fluorescence technique. In both cases, measurements were made in the presence of O 2 , N 2 or He carrier gases in a flow system, at such time after photolysis that reactions involving O( 1 D) and O 2 ( 1 ∑ g + ) had gone to completion, whereas those involving O( 3 P) and O 2 ( 1 Δ g ) had not proceeded to a significant extent. The ‘intermediate’ quantum yields for ozone photolysis in helium and oxygen are 1.9 and 1.6 respectively, referred to an assumed intermediate quantum yield for photolysis in nitrogen of 1.0. In an oxygen carrier, for every ozone molecule decomposed in the primary step there results 1.5 ± 0.1 O( 3 P) atoms. For photolysis in helium this number is approximately 0.6. The results suggest that there are two pathways for the reaction between O( 1 D) and O 3 , in one of which the products are O 2 + 2O: two O atoms are formed on approximately one-third of reactive collisions. There is no evidence for production of an excited molecular product which is reactive on the concentration-time scale of these experiments. It is shown that both the intermediate quantum yield and the [O ( 3 P)] measurements are consistent with the formation of molecular oxygen in the 1 ∑ g + state on 50 to 60% of quenching collisions between O( 1 D) and O 2 .