Combustion chemistry of methoxymethanol. Part I: Chemical kinetics of hydrogen-abstraction reactions and the unimolecular reactions of the product [C₂H₅O₂] radicals

The reaction kinetics of hydrogen-abstraction reactions from methoxymethanol (CH₃OCH₂OH) by hydrogen (Ḣ) atom, hydroxyl (ȮH), hydroperoxyl (HȮ₂), methyl (ĊH₃) and methoxyl (CH₃Ȯ) radicals, and decomposition of the related hydroxyl-methoxyl-methyl (CH₃OĊHOH), hydroxymethoxyl-methyl (ĊH₂OCH₂OH) and methoxyl-methoxy (CH₃OCH₂Ȯ) radicals, have been investigated in this study through high-level ab initio calculations. The stationary points of the potential energy surfaces have been determined at the CCSD(T)/aug-cc-pVTZ level of theory corrected by MP2/aug-cc-pVT,QZ methods, based on the optimized geometries obtained from BHandHLYP/6–311++G(d,p) method. Rate constants at temperatures from 300 to 2000 K for H-abstraction reactions by Ḣ atom, HȮ₂, ĊH₃ and CH₃Ȯ radicals have been obtained using conventional transition state theory (TST), while those for H-abstraction reactions by ȮH radical have been calculated employing variation transition state theory (VTST). It is found that the H-abstraction reactions from the secondary carbon atom of methoxymethanol are the most favored pathways. Total rate constants for H-abstraction reactions by ȮH radical are the fastest among the title H-abstraction reactions at temperatures below 1000 K, while H-abstraction reactions by Ḣ atom are more competitive at temperatures above 1200 K. Pressure-dependent rate constants at temperatures in the range of 300–2000 K and at pressures from 0.01 to 100 atm for the unimolecular reactions of CH₃OĊHOH, ĊH₂OCH₂OH and CH₃OCH₂Ȯ radicals have been obtained from Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) calculations. Temperature-dependent thermochemical properties for methoxymethanol and related radicals have been computed using a combination of composite methods.