Rate constants for the gas–phase reactions of OH radicals with ethylene and halogenated ethylene compounds

Abstract

Rate constants are reported for the reactions of OH radicals with six different ethylene compounds: C2H4, C2H3Cl, CH2CF2, C2HCl3, C2F3Cl, and C2Cl4. Measurements are made with a discharge‐flow system using laser magnetic resonance detection of OH. Rate constants are given for the reactions in a helium buffer gas over the range 0.7–7 torr at 296 K. The mechanism for the reactions appears to involve an attack by the OH radical on one of the carbon atoms, thus breaking the pi bond. The resulting activated complex may be stabilized by collision with a buffer molecule or in some cases may form a new product by ejecting a Cl atom. All of the reactions show some mixed bimolecular and termolecular behavior with some becoming totally bimolecular within the range studied. The reactions are all very fast with rate coefficients in the range (2–6) ×10−12 cm3/molecule ⋅s, except for C2Cl4 which is about 1.7×10−13 cm3/molecule ⋅s. The application of these rates and mechanisms to atmospheric chemistry is discussed.