Molecular beam‐laser induced fluorescence experiments on hydrogen abstraction from amines by O(3P)

Insights into the role of the H-abstraction reaction kinetics of amines in understanding their degeneration fates under atmospheric and combustion conditions

Amines, a class of prototypical volatile organic compounds, have garnered considerable interest within the context of atmospheric and combustion chemistry due to their substantial contributions to the formation of hazardous pollutants in the atmosphere. In the current energy landscape, the implementation of carbon-neutral energy and strategic initiatives leads to generation of new amine sources that cannot be overlooked in terms of the emission scale. To reduce the emission level of amines from their sources and mitigate their impact on the formation of harmful substances, a comprehensive understanding of the fundamental reaction kinetics during the degeneration process of amines is imperative. This perspective article first presents an overview of both traditional amine sources and emerging amine sources within the context of carbon peaking and carbon neutrality and then highlights the importance of H-abstraction reactions in understanding the atmospheric and combustion chemistry of amines from the perspective of reaction kinetics. Subsequently, the current experimental and theoretical techniques for investigating the H-abstraction reactions of amines are introduced, and a concise summary of research endeavors made in this field over the past few decades is provided. In order to provide accurate kinetic parameters of the H-abstraction reactions of amines, advanced kinetic calculations are performed using the multi-path canonical variational theory combined with the small-curvature tunneling and specific-reaction parameter methods. By comparing with the literature data, current kinetic calculations are comprehensively evaluated, and these validated data are valuable for the development of the reaction mechanism of amines.

Effects of Anharmonicity, Recrossing, Tunneling, and Pressure on the H-Abstractions from Dimethylamine by Triplets O and O2

Rate constants of the H-abstraction reactions from dimethylamine (DMA) by triplets O and O₂ are theoretically determined with the canonical variational transition-state theory (CVT). By comparing the barrier heights and reaction energies obtained from different density-functional theory methods to those computed from the gold-standard method CCSD(T)/CBS(T-Q), we identify the M08-HX/ma-TZVP method as the best with a mean unsigned deviation of 1.0 kcal mol^-1. On the basis of the optimized geometries and frequencies with the selected method, the rate constants are calculated using the CVT method combined with the multistructural torsional anharmonicity and small-curvature tunnelling (MS-CVT/SCT) options in the temperature range 200-2000 K. The calculations show that OH and HO₂ are mainly produced from the direct abstraction from the C-H bond. The multistructural torsional anharmonicity has a large contribution to the rate constants, and the effects of recrossing and tunneling at the N-site are more important than those at C-site. Additionally, given the formation of reactant complex between DMA and triplet O, the H-abstraction channel is not favored at high pressure. Our calculations with both the Polyrate and MESS codes agree with the reported data within the uncertainty.

The Dynamics of Reactions of O(3P) Atoms with Saturated Hydrocarbons and Related Compounds

We review the experimental and theoretical work which has been carried out on the dynamics of reactions of O(3P) with saturated hydrocarbons and related systems. We concentrate primarily on gas phase reactions, but also cover in less detail the more limited work on condensed phase and interfacial reactions. Although O(3P) + saturated alkane reactions are the primary focus, the dominant features of their dynamics are compared and contrasted with those of unsaturated alkanes, functionalised alkanes, and inorganic hydrides (including silanes, germanes, H2S, and hydrogen halides). The principal experimental techniques are reviewed. The experimentally determined quantities are identified, including excitation functions, OH rovibrational and fine-structure partitioning, the rather limited equivalent results for the organic radical co-product, and differential cross-sections. The dynamical conclusions that have been inferred are discussed and compared with the predictions of various levels of theory from semi-empirical models through to rigorous ab initio treatments. For many organic systems, most of the evidence points to OH being formed via a direct abstraction mechanism in which the O(3P) atom attacks along an isolated C–H bond. Outstanding problems with this basic interpretation and gaps in the current knowledge base are identified.

State-to-state dynamics of the Cl+CH3OH→HCl+CH2OH reaction

Molecular chlorine, methanol, and helium are co-expanded into a vacuum chamber using a custom designed "late-mixing" nozzle. The title reaction is initiated by photolysis of Cl2 at 355 nm, which generates monoenergetic Cl atoms that react with CH3OH at a collision energy of 1960 +/- 170 cm(-1) (0.24 +/- 0.02 eV). Rovibrational state distributions of the nascent HCl products are obtained via 2 + 1 resonance enhanced multiphoton ionization, center-of-mass scattering distributions are measured by the core-extraction technique, and the average internal energy of the CH3OH co-products is deduced by measuring the spatial anisotropy of the HCl products. The majority (84 +/- 7%) of the HCl reaction products are formed in HCl(v = 0) with an average rotational energy of [Erot] = 390 +/- 70 cm(-1). The remaining 16 +/- 7% are formed in HCl(v = 1) and have an average rotational energy of [Erot] = 190 +/- 30 cm(-1). The HCl(v = 1) products are primarily forward scattered, and they are formed in coincidence with CH2OH products that have little internal energy. In contrast, the HCl(v = 0) products are formed in coincidence with CH2OH products that have significant internal energy. These results indicate that two or more different mechanisms are responsible for the dynamics in the Cl + CH3OH reaction. We suggest that (1) the HCl(v = 1) products are formed primarily from collisions at high impact parameter via a stripping mechanism in which the CH2OH co-products act as spectators, and (2) the HCl(v = 0) products are formed from collisions over a wide range of impact parameters, resulting in both a stripping mechanism and a rebound mechanism in which the CH2OH co-products are active participants. In all cases, the reaction of fast Cl atoms with CH3OH is with the hydrogen atoms on the methyl group, not the hydrogen on the hydroxyl group.