High-accuracy theoretical studies on the gas-phase reaction mechanisms of sulfur mustard with reactive oxygen species (OH/O ₂ /HO ₂ /O)

The gas-phase reaction mechanisms of sulfur mustard (HD) under oxygenated conditions constitute the theoretical foundation for understanding its environmental evolution processes and evaluating its incineration efficiency. In this work, the gas-phase reaction mechanisms and kinetics between HD and reactive oxygen species (OH, O₂, HO₂, O) were investigated at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(d,p) theoretical level. The study reveals that all four oxygen species can participate in hydrogen abstraction reactions with HD, with the OH-mediated and O-mediated pathways being the most favorable. Furthermore, the research demonstrates that O₂ and O can directly oxidize HD to form mustard sulfoxide, which can be further oxidized to mustard sulfone - a compound exhibiting comparable toxicity to HD itself. The HD-OH adduct can be converted to mustard sulfoxide in the presence of O₂, and the resulting sulfoxide-OH adduct can subsequently be oxidized to mustard sulfone. Computational analysis of the reaction pathways employing the RS2C method indicates that both steps proceed <i>via</i> substantially high energy barriers. Kinetic simulations show that under typical incineration conditions, OH and O play dominant roles in HD degradation.