Abstract

A study of the flash photolysis of chlorine monoxide and of its photosensitized decomposition by chlorine and bromine has yielded rate constants for the reactions Cl + Cl₂O --> Cl₂ + ClO, k₁ = 4.1 × 10⁸ l mol^-1 s^-1, Br + Cl₂O --> BrCl + ClO, k₉ = 6.1 × 10⁸ l mol^-1 s^-1, ClO + Cl₂O --> ClO₂ + Cl₂, k₃ = 2.6 × 10⁵ l mol^-1 s^-1, ClO + Cl₂O --> Cl₂ + O₂ + Cl, k₄ = 6.5 × 10⁵ l mol^-1 s^-1, 2ClO --> Cl₂ + O₂, k₂ = 2.8 × 10⁷ l mol^-1 s^-1. The quantum yield for the decomposition of chlorine monoxide was measured in each of the three systems and is quantitatively accounted for by the reactions given. The ClO free radical has been flash photolysed and the production of vibrationally excited oxygen in the reaction O + ClO --> Cl + O₂^* (v^{' '}<= 14), k₁₁ = 7.5 × 10⁹ l mol^-1s^-1 demonstrated. The same reaction is responsible for the production of O₂^* in the flash photolysis of Cl₂O with radiation below ~ 300 nm. The relaxation of O₂^* by chlorine atoms is exceptionally efficient, with a rate constant for v^{' '} = 12 in excess of 2 × 10⁹ l mol^-1 s^-1. The corresponding rate constant for relaxation by Cl₂O is < 10⁸ l mol^-1 s^-1.