TY - JOUR
T1 - Ab Initio Reaction Kinetics of CH3OC(=O) and CH2OC(=O)H Radicals
AU - Tan, Ting
AU - Yang, Xueliang
AU - Ju, Yiguang
AU - Carter, Emily A.
N1 - Funding Information:
This work was supported by the Combustion Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, and the Office of Basic Energy Sciences under Award Number DE-SC0001198. The authors thank Dr. S. J. Klippenstein for very helpful discussions.
Publisher Copyright:
© 2015 American Chemical Society.
PY - 2016/3/3
Y1 - 2016/3/3
N2 - The dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonyl radical (CH3OC(=O)) and (formyloxy)methyl radical (CH2OC(=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 multiconfigurational 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 Arrhenius expressions. Dissociation of CH3OC(=O) to CH3 and CO2 is predicted to be much faster than dissociating to CH3O and CO, consistent with its greater exothermicity. Isomerization between CH3OC(=O) and CH2OC(=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 CH3O removal mechanisms under atmospheric conditions, the reaction kinetics of CH3O + CO was also studied along the PES of CH3OC(=O); the resulting kinetics predictions are in remarkable agreement with experiments.
AB - The dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonyl radical (CH3OC(=O)) and (formyloxy)methyl radical (CH2OC(=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 multiconfigurational 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 Arrhenius expressions. Dissociation of CH3OC(=O) to CH3 and CO2 is predicted to be much faster than dissociating to CH3O and CO, consistent with its greater exothermicity. Isomerization between CH3OC(=O) and CH2OC(=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 CH3O removal mechanisms under atmospheric conditions, the reaction kinetics of CH3O + CO was also studied along the PES of CH3OC(=O); the resulting kinetics predictions are in remarkable agreement with experiments.
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U2 - 10.1021/acs.jpcb.5b07959
DO - 10.1021/acs.jpcb.5b07959
M3 - Article
C2 - 26413728
AN - SCOPUS:84957542761
SN - 1520-6106
VL - 120
SP - 1590
EP - 1600
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 8
ER -