Ab initio kinetics of the CH 3 NH + NO 2 reaction: formation of nitramines and N -alkyl nitroxides.

This study provides a detailed understanding of how the reaction between CH 3 NH, one of the primary products of the CH 3 NH 2 + OH/Cl reactions, and NO x occurs in the atmosphere since the reaction is expected to be a dominant sink for the tropospheric CH 3 NH radical. First, we focus on the reaction of the aminyl radical CH 3 NH with NO 2 , complementing the known reaction between CH 3 NH and NO, to provide the overall picture of the CH 3 NH + NO x system. The reaction was meticulously examined across the extended range of temperature (298-2000 K) and pressure (0.76-76 000 torr) using quantum chemistry calculations and kinetic modeling based on the framework of the Rice-Ramsperger-Kassel-Marcus (RRKM)-based master equation. Highly correlated electronic structure calculations unveil that the intricate reaction mechanism of the CH 3 NH + NO 2 reaction, which can proceed through O-addition or N-addition to form NO 2 , encompasses numerous steps, channels, and various intermediates and products. The temperature-/pressure-dependent kinetic behaviors and product distribution of the CH 3 NH + NO 2 reaction are revealed under atmospheric and combustion conditions. The main products under atmospheric conditions are found to be CH 3 NHO and NO, as well as CH 3 NHNO 2 , while under combustion conditions, the primary products are only CH 3 NHO and NO. Given its stability under ambient conditions, CH 3 NHNO 2 , a nitramine, is believed to have the potential to induce DNA damage, which can ultimately result in severe cancers. Secondly, by building upon prior research on the CH 3 NH + NO system, this study shows that the reaction of CH 3 NH with NO x holds greater importance in urban areas with elevated NO x emissions than other oxidants like O 2 . Furthermore, this reaction occurs swiftly and results in the creation of various compounds, such as the carcinogenic nitrosamine (CH 3 NHNO), carcinogenic nitramine (CH 3 NHNO 2 ), CH 3 NNOH, (CH 3 NN + H 2 O) and (CH 3 NHO + NO).