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, 2ClO→ lim 4′Cl–O–O+Cland by ClO–N2O→N2+Cl–O–Ofollowed by Cl–O–O+M→Cl+O2+MIt 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 ΔHf0=21±2 kcal, Sf0=61 cal/mole—°K, with a bond-dissociation energy, D(Cl—OO)=8±2 kcal.