Theoretical study of the NO3 radical reaction with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2

The potential reaction of nitrate radical (NO3), the main nighttime atmospheric oxidant, with five alkyl halides, halons (CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2) has been studied theoretically. The most favorable reaction corresponds to a hydrogen transfer. The stationary points on the potential energy surfaces of these reactions have been characterized. The reactions can be classified into two groups based on the number of hydrogen atoms in the halon molecules (1 or 2). The reactions with halons with only one hydrogen atom show more exothermic profiles than those with two hydrogens. The kinetics of the reaction of NO3 + CH2BrI was then studied using a multi-well Master Equation solver, since this is the reaction that should be fastest at tropospheric temperatures. These results indicate that, in the case of NO3-polluted atmospheric conditions this reaction would be much slower than NO3 radical photodissociation.