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This study provides a detailed understanding of how the reaction between CH3NH, one of the primary products of the CH3NH2 + OH/Cl reactions, and NOx occurs in the atmosphere since the reaction is expected to be a dominant sink for the tropospheric CH3NH radical. First, we focus on the reaction of the aminyl radical CH3NH with NO2, complementing the known reaction between CH3NH and NO, to provide the overall picture of the CH3NH + NOx 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 CH3NH + NO2 reaction, which can proceed through O-addition or N-addition to form NO2, encompasses numerous steps, channels, and various intermediates and products. The temperature-/pressure-dependent kinetic behaviors and product distribution of the CH3NH + NO2 reaction are revealed under atmospheric and combustion conditions. The main products under atmospheric conditions are found to be CH3NHO and NO, as well as CH3NHNO2, while under combustion conditions, the primary products are only CH3NHO and NO. Given its stability under ambient conditions, CH3NHNO2, 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 CH3NH + NO system, this study shows that the reaction of CH3NH with NOx holds greater importance in urban areas with elevated NOx emissions than other oxidants like O2. Furthermore, this reaction occurs swiftly and results in the creation of various compounds, such as the carcinogenic nitrosamine (CH3NHNO), carcinogenic nitramine (CH3NHNO2), CH3NNOH, (CH3NN + H2O) and (CH3NHO + NO). [ABSTRACT FROM AUTHOR]

Cyclic saturated ethers are proposed as alternative fuels for future sustainability. In particular, dioxolanes have been identified as promising biofuel candidates. However, pyrolysis and oxidation of dioxolanes are not well understood. In this work, we measured the temperature-dependent absorption cross-section of 1,3-dioxolane (13DO) in the mid-IR region over 8.4 – 10.5 μm (950 –1190 cm−1). We applied the spectroscopic knowledge to investigate the temperature and pressure dependence of the rate coefficients of the unimolecular decomposition of 13DO over the temperature range of 1000–1400 K and pressures near 0.7 and 2.4 bar. We employed a rapidly tuning MIRcat-QT™ laser in conjugation with a shock tube to carry out high-temperature spectroscopic and pyrolysis measurements. Measured IR spectra of 13DO exhibited a strong temperature dependence. For the kinetic study, we employed the vibrational feature of 13DO near 1120.5 cm−1 to monitor the decay of 13DO quantitatively. The measured rate coefficients did not show any discernible pressure dependence. This indicates that the rate coefficients of the unimolecular decomposition of 13DO are close to the high-pressure limit under the present experimental conditions. In addition, we rationalized the temperature and pressure dependence of the reaction by employing electronic structure/RRKM-ME calculations. Our theoretical model accurately captured the experimental trends of the rate coefficients of the unimolecular decomposition of 13DO. [ABSTRACT FROM AUTHOR]

Alkylated aromatics are ubiquitous in transportation fuels. 1,3,5-Trimethyl benzene (135TMB) is a popular surrogate for the aromatic content of distillate fuels due to its symmetry (point group, C 3h), which facilitates the construction of an accurate chemical kinetic model. The reaction of OH radicals with 135TMB plays a crucial role in the oxidation kinetics of 135TMB. In this work, the reaction kinetics of OH-initiated oxidation of 135TMB were investigated behind reflected shock waves over 975–1318 K and atmospheric pressure. The reaction was followed by monitoring OH radicals near 307 nm. The rate coefficients were extracted from detailed chemical kinetic modeling of OH concentration-time profiles. Our measured data clearly showed a positive temperature dependence, in contrast to the negative temperature dependence of the literature low-temperature data. At 1000 K, our measured rate coefficient is 1.3 × 10−11 cm3 molecule−1 s−1, which is roughly a factor of 5 lower than the room-temperature data reported in the literature. This observation reflects the complex nature of the OH + 135TMB reaction, similar to that observed for various aromatics + OH chemical systems. Our measurements did not show any discernible pressure dependence over the narrow pressure range of 870 – 1148 Torr. The title reaction has several possible channels in the reactive potential energy surface. The importance of each channel was characterized using ab initio/RRKM-ME calculations over T = 200–2000 K and P = 0.76 -7600 Torr. Our analyses revealed that addition channels and hydrogen abstraction from the methyl site have negative energy barriers. The reaction was found to undergo almost exclusively (∼93%) via the addition channel under ambient conditions. However, beyond 600 K, the abstraction channels take the lead, yielding the positive T -dependence of the overall rate coefficient. Although addition channels display a sharp fall-off behavior beyond 500 K, the general rate coefficients are pressure-independent. The title reaction shows a complex kinetic behavior due to competing channels whose contribution changes significantly with temperature. Our theoretical calculations nicely reproduced the complex T -dependence of the reaction. After adjusting the barrier height, our theory remarkably captured the positive T -dependence of our high- T kinetic data and the negative T -dependence of the low- T literature data. To our knowledge, this is the first detailed study on the reaction kinetics of 135TMB with OH radicals. The reported rate data will be helpful for the combustion modeling of alkylated aromatic species. [ABSTRACT FROM AUTHOR]