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Atmospheric Oxidation of CH 3 Br: Chemistry of the CH 2 BrO Radical

1996; American Chemical Society; Volume: 100; Issue: 17 Linguagem: Inglês

10.1021/jp951813q

1541-5740

John J. Orlando, Geoffrey S. Tyndall, Timothy J. Wallington,

Atmospheric and Environmental Gas Dynamics

The Cl-atom-initiated photooxidation mechanism of CH3Br has been investigated in chamber experiments conducted under conditions applicable to the lower atmosphere. Major carbon-containing products obtained in the presence of O2 and NO, as determined by FTIR absorption spectroscopy, are CH2O and CO. In addition, HC(O)Br is observed in the absence of NO. At low temperature, in the presence of NO, CH2BrO2NO2 was also identified as a reaction product. The results are used to determine the fate of the alkoxy radical, CH2BrO. It is found that unimolecular decomposition of CH2BrO to CH2O + Br is the dominant process in 1 atm of O2 at all temperatures studied (between 228 and 298 K), while reaction with O2, CH2BrO + O2 → HC(O)Br + HO2, and the three-centered elimination of HBr, CH2BrO → HCO + HBr, are found to be minor pathways under these conditions (less than 5% each). Assumption of a rate constant of 6 × 10-14 cm3 molecule-1 s-1 for the reaction of CH2BrO with O2 (DeMore, W. B., et al. NASA JPL Publ. 1994, No. 94-26) provides a lower limit to the rate of Br-atom elimination of 3 × 107 s-1 at 228 K, 1 atm of pressure.