Ab Initio Reaction Kinetics of CH ₃ O$$\dot{C}$$(=O) and $$\dot{C}$$H ₂ OC(=O)H Radicals

Journal Article · Thu Mar 03 00:00:00 EST 2016 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI:https://doi.org/10.1021/acs.jpcb.5b07959· OSTI ID:1369801

Tan, Ting; Yang, Xueliang; Ju, Yiguang; Carter, Emily A.

The dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonyl radical (CH3O$$\dot{C}$$(=O)) and (formyloxy)methyl radical ($$\dot{C}$$H2OC(=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 CH3O$$\dot{C}$$(=O) to $$\dot{C}$$H3 and CO2 is predicted to be much faster than dissociating to CH3$$\dot{O}$$ and CO, consistent with its greater exothermicity. Isomerization between CH3O$$\dot{C}$$(=O) and $$\dot{C}$$H2OC(=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$$\dot{O}$$ removal mechanisms under atmospheric conditions, the reaction kinetics of CH3$$\dot{O}$$ + CO was also studied along the PES of CH3O$$\dot{C}$$(=O); the resulting kinetics predictions are in remarkable agreement with experiments.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Combustion Energy Frontier Research Center (CEFRC)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: SC0001198
• OSTI ID: 1369801
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 120, Issue 8; Related Information: CEFRC partners with Princeton University (lead); Argonne National Laboratory; University of Connecticut; Cornell University; Massachusetts Institute of Technology; University of Minnesota; Sandia National Laboratories; University of Southern California; Stanford University; University of Wisconsin, Madison; ISSN 1520-6106
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY