H Atom Abstractions from C₁-C₄ Alcohols, Aldehydes, and Ethers by NO₂: Ab Initio and Comprehensive Kinetic Modeling

As crucial additives and intermediates, alcohols, ethers, and aldehydes play significant roles in the combustion process. However, the chemistry of NO_X/hydrocarbon interactions and the rate rules governing these interactions remain largely unexplored in this combustion system. To address this gap, this study provides a comprehensive investigation of H atom abstraction by NO₂ from C₁-C₄ alcohols, aldehydes, and ethers that leads to the formation of three HNO₂ isomers (i.e., trans-HONO, HNO₂, and cis-HONO), encompassing nine hydrocarbons and over 50 reactions. Utilizing the DLPNO-CCSD(T)/cc-pVDZ//M06-2X/6-311++g(d,p) method, the electronic structures, single-point energies, C-H bond dissociation energies, and 1D hindered rotor potentials of the reactants, transition states, complexes, and products in each reaction are computed. The potential energy surfaces and energy barriers for each reaction are determined based on these calculations. Subsequently, the rate coefficients for all studied reactions are derived using transition state theory, implemented with the Master Equation System Solver program, across a temperature range from 298.15 to 2000 K. A thorough analysis of branching ratios highlights the differences and similarities between species, HNO₂ isomers, and abstraction sites, leading to the establishment of consistent rate rules that can be used for rate estimation by analogy for a wider range of oxygenated species. Adding these H atom abstractions to the chemical kinetic model improves the model reactivity and advances the ignition, as indicated by the reduction in the ignition delay time for species that initially lacked these reactions. Further sensitivity and flux analyses highlight the crucial role of H atom abstraction by NO₂. The findings underscore the importance of accurately incorporating these kinetic parameters into newly developed chemical models for alcohols, aldehydes, and ethers. Additionally, this study highlights the need for future experimental efforts to investigate the effects of NO₂ on the combustion systems of these compounds.