Kinetics of the reactions of the HO2 radical with peroxyl radicals derived from hydrochlorofluorocarbons and hydrofluorocarbons

Abstract

Rate coefficients have been obtained for the reactions of HO₂ with peroxyl radicals, RO₂, derived from the hydrochlorofluorocarbons : HCFC-22 (CHF₂Cl), HCFC-141b (CH₃CFCl₂) and HCFC-142b (CH₃CF₂Cl), and the hydrofluorocarbons : HFC-125 (CF₃CHF₂) and HFC-134a (CF₃CH₂F). The kinetics of the reactions were studied at room temperature using the laser flash photolysis technique with UV absorption detection. The radicals were generated following the 248 nm laser photolysis of mixtures containing H₂O₂–O₂–N₂ and the HCFC or HFC of interest. From an analysis of the transient absorption profiles recorded, the following kinetic parameters were derived for the reaction, RO₂± HO₂→ products : k=(3.4 ± 1.7)× 10^–12 cm³ molecule^–1 s^–1(R = CF₂Cl), k=(9.2 ± 4.6)× 10^–12 cm³ molecule^–1 s^–1(R = CFCl₂CH₂), k=(6.8 ± 3.4)× 10^–12 cm³ molecule^–1 s^–1(R = CF₂ClCH₂), k=(1.2 ± 0.6)× 10^–12 cm³ molecule^–1 s^–1(R = CF₃CF₂) and k=(4.0 ± 2.0)× 10^–12 cm³ molecule^–1 s^–1(R = CF₃CHF). (The quoted uncertainties are ±2σ). An upper limit for the rate coefficient of CF₃O₂ with HO₂(k < 2 × 10^–12 cm³ molecule^–1 s^–1) was inferred from an analysis of the HFC-134a datasets.