Ab Initio Reaction Kinetics of CH3O(C) over dot(=O) and CH2O(C) over dot(=O)H Radicals

作者：Tan Ting; Yang Xueliang; Ju Yiguang; Carter Emily K

来源：Journal of Physical Chemistry B, 2016, 120(8): 1590-1600.

DOI：10.1021/acs.jpcb.5b07959

The dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonyl radical (CH3O(C) over dot(=O)) and (formyloxy)methyl radical ((C) over dotH(2)OC(=O)H) are investigated theoretically using high-level ab initio methods and Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) theory. Geometries obtained at the hybrid density functional theory (DFT) and coupled cluster singles and doubles with perturbative triples correction (CCSD(T)) levels of theory are found to be similar. We employ high-level ab initio wave function methods to refine the potential energy surface: CCSD(T), multireference singles and doubles configuration interaction (MRSDCI) with the Davidson-Silver (DS) correction, and multireference averaged coupled-pair functional (MRACPF2) theory. MRSDCI+DS and MRACPF2 capture the multiconfiguratonal character of transition states (TSs) and predict lower barrier heights than CCSD(T). The temperature- and pressure dependent rate coefficients are computed using RRKM/ME theory in the temperature range 300-2500 K and a pressure range of 0.01 atm to the high-pressure limit, which are then fitted to modified Arr.henius expressions. Dissociation of CH3O(C) over dot(=O) to (C) over dotH(3) and CO2 is predicted to be much faster than dissociating to CH3(O) over dot and CO, consistent with its greater exothermicity. Isomerization between CH3O(C) over dot(=O) and (C) over dotH(2)OC(=O)H is predicted to be the slowest among the studied reactions and rarely happens even at high temperature and high pressure, suggesting the decomposition pathways of the two radicals are not strongly coupled. The predicted rate coefficients and branching fractions at finite pressures differ significantly from the corresponding high-pressure-limit results, especially at relatively high temperatures. Finally, because it is one of the most important CH3(O) over dot removal mechanisms under atmosp

• 出版日期2016-3-3