Abstract. The atmospheric reactions of halogenated formaldehydes with halogen atoms were investigated by high-accuracy molecular orbital calculation. Our studies showed that compared to X-addition pathway, the H-abstraction pathway was demonstrated to be more preferred to form halogenated formyl radicals and hydrogen halides (HX). In specific areas with abundant halogen atoms, such as the marine boundary layer (MBL), halogenated formyl radical was reacted easily with halogen atoms and finally transformed into HX and CO2 in the presence of water; otherwise, this radical was degraded to CO2, halogen gas, and halogenated oxide in the presence of O2 and halogen atoms. By using the canonical variational transition state theory, the kinetics calculations were performed within a wide atmospheric temperature range of 200–368 K, and theoretical values agreed well with the available experimental data. Under atmospheric conditions, rate constants decreased as altitude increased, and especially the rate constants of halogen atoms reacted with FCHO quickly reduced. The kinetic results showed that although the reactions of halogenated formaldehydes with F atoms occurred more easily than did those with Cl and Br atoms, the two latter reactions were still important atmospheric degradation process, especially in the MBL. The modified Arrhenius equations of rate constants within the atmospheric temperature range were fitted, which helped to understand the established atmospheric model and estimated the contribution of title reactions to atmospheric chemistry pollution.

The atmospheric reactions of halogenated formaldehydes with halogen atoms were investigated by high-accuracy molecular orbital calculation. Studies showed that halogen atoms could easily abstract hydrogen atom from halogenated formaldehydes to form halogenated formyl radical and hydrogen halide (HX). In specific areas with high concentration of halogen atoms, such as the marine boundary layer (MBL), halogenated formyl radical was easily to react with halogen atoms and finally transformed into HX and CO₂ in the presence of water; otherwise, this radical was degraded to CO₂, halogen gas, and halogenated oxide. By using the canonical variational transition state theory, the kinetics calculations were performed within a wide atmospheric temperature range of 200–368 K, and theoretical values agreed well with the available experimental data. Under atmospheric conditions, the rate constants decreased as altitude increased, and especially the rate constants of halogen atoms reaction with FCHO quickly reduced. Although the reactions of halogenated formaldehydes with F atoms were more easily occurred than did those with Cl and Br atoms, the two latter reactions were still important atmospheric degradation process, especially in the MBL. The modified Arrhenius formulas of rate constants within the atmospheric temperature range were fitted, which helped to understand the established atmospheric model and estimate the contribution of title reactions to atmospheric chemistry pollution

■ METHODSSelection of Methods. In this work, at least 40 pathways have been calculated for the title reactions. Although the calculated time of energies for every stationary point needed for high-accuracy methods were not too long, the cumulative time for all of these stationary points were huge and not neglectable. Thus, the developments of a suitable method to balance the relationship between the computational accuracy and the computational expensive were very necessary. (Table S1). The QCISD(T) method, a costly single-point energy (SPE) calculation method coupled with a large basis set [6-311+G(3df,2p)], could effectively minimize the error from the correlation of electrons and spin contamination effect in SPE calculation (Szabo et al., 1997). The computational results indicated that the values of PMP2//MP2 level are more closer to the values of QCISD(T) level than those of MP2//MP2 level, within the error limit of 0.47 kcal/mol. Thus, to meet the need of both high accuracy and low computational cost, the