Combustion chemistry of methoxymethanol. Part Ⅰ: Chemical kinetics of hydrogen-abstraction reactions and the unimolecular reactions of the product C_2H_5O_2 radicals

摘要

The reaction kinetics of hydrogen-abstraction reactions from methoxymethanol (CH_3OCH_2OH) by hydrogen(H) atom, hydroxyl (OH), hydroperoxyl (HO_2), methyl (CH_3) and methoxyl (CH_3O) radicals,and decomposition of the related hydroxyl-methoxyl-methyl (CH_3OCHOH), hydroxymethoxyl-methyl(CH_2OCH_2OH) and methoxyl-methoxy (CH_3OCH_2O) radicals, have been investigated in this study throughhigh-level ab initio calculations. The stationary points of the potential energy surfaces have been determinedat the CCSD(T)/aug-cc-pVTZ level of theory corrected by MP2/aug-cc-pVT,QZ methods, based onthe optimized geometries obtained from BHandHLYP/6-311 ++ G(d,p) method. Rate constants at temperaturesfrom 300 to 2000K for H-abstraction reactions by H atom, HO_2 , CH_3 and CH_3O radicals havebeen obtained using conventional transition state theory (TST), while those for H-abstraction reactionsby OH radical have been calculated employing variation transition state theory (VTST). It is found thatthe H-abstraction reactions from the secondary carbon atom of methoxymethanol are the most favoredpathways. Total rate constants for H-abstraction reactions by OH radical are the fastest among the titleH-abstraction reactions at temperatures below 1000K, while H-abstraction reactions by H atom aremore competitive at temperatures above 1200 K. Pressure-dependent rate constants at temperaturesin the range of 300-2000K and at pressures from 0.01 to 100 atm for the unimolecular reactionsof CH_3OCHOH, CH_2OCH_2OH and CH_3OCH_2O radicals have been obtained from Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) calculations. Temperature-dependent thermochemical properties formethoxymethanol and related radicals have been computed using a combination of composite methods.