Kinetic and Mechanistic Study of the Reactions of Atomic Chlorine with C2H5Br, n- C3H7Br, and 1,2-C2H4Br2

Halogenated alkanes are present in our atmosphere as a result of both natural and anthropogenic sources. The bromoalkanes ethyl bromide (CH3CH2Br), n-propylbromide (CH3CH2CH2Br), and 1,2-dibromoethane (CH2BrCH2Br) are emitted into the atmosphere from anthropogenic sources, and are thought to play a role in stratospheric ozone depletion. While the primary tropospheric sink for the above bromocarbons is reaction with OH radicals, reaction with chlorine atoms may also represent a non-negligible sink. We have coupled production of Cl by laser flash photolysis with time-resolved monitoring of Br atom appearance by atomic resonance fluorescence spectroscopy to study the kinetics of the title reactions over a wide range of temperature and pressure. Atomic Br is generated by rapid dissociation of the CH2CH2Br product of Cl + CH3CH2Br, the CH3CHCH2Br product of Cl + CH3CH2CH2Br, and the only possible H-abstraction product of Cl + CH2BrCH2Br. By comparing product Br signal strengths with those obtained when Cl removal is dominated by reaction with Br2, temperature-dependent branching ratios for abstraction of the â hydrogen are obtained for the Cl + CH3CH2Br and Cl + CH3CH2CH2Br reactions.