Investigation of the Atmospheric Oxidation Pathways of Bromoform:  Initiation via OH/Cl Reactions

The tropospheric oxidation pathways of bromoform, CHBr 3, initiated via reaction with OH and Cl, have been examined computationally with energetics calculated for each mechanistic step up to the liberation of all three bromine atoms. We have calculated the energetics associated with the addition of O 2 to CBr 3 and the subsequent addition of NO to CBr 3 O 2 to form an energized peroxy nitrite molecule. The peroxy nitrite molecule is predicted to dissociate rapidly to form CBr 3 O and NO 2, and the energetics and kinetics of this step were also determined. We find that the reaction of CBr 3 O 2 with HO 2 may directly lead to significant production of CBr 3 O, a pathway that is not important in alkyl analogues. We have examined the dissociation of the CBr 3 O radical at a higher level of theory to accurately quantify the activation energy and exothermicity of the dissociation. On the basis of our results, we predict that the CBr 3 O radical will dissociate rapidly to form Br and CBr 2 O. The tropospheric and stratospheric impact of bromoform oxidation is discussed in light of the present results.