Theoretical study of H-atom abstraction by CH3OȮ radicals from aldehydes and alcohols: Ab initio and comprehensive kinetic modeling

Abstract

Reaction kinetics of H-atom abstraction from C1C3 alcohols, including CH3OH, C2H5OH, NC3H7OH, IC3H7OH, and C1C2 aldehydes, including CH2O, CH3CHO, by CH3OȮ radicals is investigated in this work through high-level ab initio calculations. Electronic structure optimizations are performed for all the stationary points with M06–2X/6−311++g(d,p) method. Quadratic configuration interaction method QCISD(T)/cc-pVXZ (where X = D and T) and Møller–Plesset perturbation theory MP2/cc-pVXZ (where X = D, T, and Q) are used to calculate single point energies. Subsequently, rate coefficients for all H-atom abstraction channels are determined using conventional transition state theory with unsymmetric tunneling corrections. These calculated results are updated to a recently updated model and then compared against expansive experimental datasets to investigate their influence on the model prediction performance. The updated model shows obvious discrepancies with the original model, where the updated model is less reactive for CH3CHO, C2H5OH, NC3H7OH, and IC3H7OH, while showing negligible differences for CH3OH and CH2O due to the lack of CH3OȮ radical formation. Sensitivity and flux analyses are further conducted, through which the difference between the studied species in their oxidation pathways and the relative importance of H-atom abstraction by CH3OȮ radicals is highlighted. With the updated rate parameters, the branching ratios of H-atom abstractions from CH2O and CH3CHO are significantly altered for CH3CHO, C2H5OH, NC3H7OH and IC3H7OH, with an obvious shift away from the abstraction channel by CH3OȮ. Further analyses highlight the critical roles of CH2O and CH3CHO chemistry as core chemistries for large hydrocarbons (e.g., carbon number > 1), which have been inadequately described in existing chemistry models. Systematic efforts are urgently needed to improve the existing CH2O and CH3CHO chemistries.