Halogen-Catalyzed Decomposition of N2O and the Role of the Hypohalite Radical

Abstract

It is shown that the Cl₂ catalyzed decomposition of N₂O cannot be explained by a nonchain reaction but is consistent with a Cl atom chain in which Cl atoms are regenerated by the reactions, $$2\mathrm{ClO}\to {\displaystyle {lim}_{4^{\prime }}}\mathrm{Cl}–\mathrm{O}–\mathrm{O}+\mathrm{Cl}$$ and by $$\mathrm{ClO}–{\mathrm{N}}_2\mathrm{O}\to {\mathrm{N}}_2+\mathrm{Cl}–\mathrm{O}–\mathrm{O}$$ followed by $$\mathrm{Cl}–\mathrm{O}–\mathrm{O}+\mathrm{M}\to \mathrm{Cl}+{\mathrm{O}}_2+\mathrm{M}$$ It is proposed that the peroxy radical Cl–O–O is the unstable intermediate responsible for the high efficiency observed for O₂ in catalyzing the recombination of Cl atoms. It is also proposed that at low temperatures O₂ should be an efficient catalyst for the generation of Cl atoms via the reaction O₂+Cl₂→ O—O—Cl+Cl. The peroxy ClOO species is shown to be a reasonable one to account for the high‐rate constant observed for reaction 4′ and for the chain decompositions of Cl₂O and OClO. Its thermodynamic properties are estimated as ΔH_f⁰=21±2 kcal, S_f⁰=61 cal/mole—°K, with a bond‐dissociation energy, D(Cl—OO)=8±2 kcal.