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Title: Ab Initio Unimolecular Reaction Kinetics of CH 2C(=)OCH 3 and CH 3C(=O)OCH 2 Radicals

Abstract

The unimolecular dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonylmethyl (CH 2C(=O)OCH 3) and acetyloxylmethyl (CH 3C(=O)OCH 2) are theoretically investigated using high-level ab initio methods and the Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) theory. Potential energy surfaces (PESs) are obtained using coupled cluster singles and doubles with perturbative triples correction (CCSD(T)), multireference singles and doubles configuration interaction (MRSDCI) with the Davidson–Silver (DS) correction, and multireference averaged coupled pair functional (MRACPF2) theory. The transition states exhibit high T1 diagnostics in coupled cluster calculations, suggesting the need for a multireference correlated wave function treatment. MRSDCI+DS and MRACPF2 capture their multiconfigurational character well, yielding lower barrier heights than CCSD(T) for these reactions. Additionally, the rate coefficients are computed using the RRKM/ME theory over a 500–2500 K temperature range and at a pressure range of 0.01 atm to the high-pressure limit. The temperature- and pressure-dependent rate coefficients are given in modified Arrhenius expressions. The β-scission of CH 2C(=O)OCH 3 is predicted to have a much higher barrier than the corresponding isomerization reaction and the β-scission of CH 3C(=O)OCH 2. Consequently, the rate coefficients for β-scission of CH 2C(=O)OCH 3 are the smallest among the three reactions and the isomerization followed by decompositionmore » to CH 3C(=O) and HCHO is the dominant reaction pathway for CH 2C(=O)OCH 3. Furthermore, both radicals CH 2C(=O)OCH 3 and CH 3C(=O)OCH 2 are predicted to mainly decompose to CH 3C(=O) + HCHO rather than to the bimolecular product CH 2C(=O) + CH 3O. A newly developed MA combustion mechanism, using our theoretical rate coefficients for the MA-related reactions, predicts combustion properties in good agreement with available experimental data.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Princeton Univ., NJ (United States)
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Combustion Energy Frontier Research Center (CEFRC)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1369802
Grant/Contract Number:  
SC0001198
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 119; Journal Issue: 42; 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; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Tan, Ting, Yang, Xueliang, Ju, Yiguang, and Carter, Emily A. Ab Initio Unimolecular Reaction Kinetics of CH2C(=)OCH3 and CH3C(=O)OCH2 Radicals. United States: N. p., 2015. Web. doi:10.1021/acs.jpca.5b08331.
Tan, Ting, Yang, Xueliang, Ju, Yiguang, & Carter, Emily A. Ab Initio Unimolecular Reaction Kinetics of CH2C(=)OCH3 and CH3C(=O)OCH2 Radicals. United States. doi:10.1021/acs.jpca.5b08331.
Tan, Ting, Yang, Xueliang, Ju, Yiguang, and Carter, Emily A. Mon . "Ab Initio Unimolecular Reaction Kinetics of CH2C(=)OCH3 and CH3C(=O)OCH2 Radicals". United States. doi:10.1021/acs.jpca.5b08331. https://www.osti.gov/servlets/purl/1369802.
@article{osti_1369802,
title = {Ab Initio Unimolecular Reaction Kinetics of CH2C(=)OCH3 and CH3C(=O)OCH2 Radicals},
author = {Tan, Ting and Yang, Xueliang and Ju, Yiguang and Carter, Emily A.},
abstractNote = {The unimolecular dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonylmethyl (CH2C(=O)OCH3) and acetyloxylmethyl (CH3C(=O)OCH2) are theoretically investigated using high-level ab initio methods and the Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) theory. Potential energy surfaces (PESs) are obtained using coupled cluster singles and doubles with perturbative triples correction (CCSD(T)), multireference singles and doubles configuration interaction (MRSDCI) with the Davidson–Silver (DS) correction, and multireference averaged coupled pair functional (MRACPF2) theory. The transition states exhibit high T1 diagnostics in coupled cluster calculations, suggesting the need for a multireference correlated wave function treatment. MRSDCI+DS and MRACPF2 capture their multiconfigurational character well, yielding lower barrier heights than CCSD(T) for these reactions. Additionally, the rate coefficients are computed using the RRKM/ME theory over a 500–2500 K temperature range and at a pressure range of 0.01 atm to the high-pressure limit. The temperature- and pressure-dependent rate coefficients are given in modified Arrhenius expressions. The β-scission of CH2C(=O)OCH3 is predicted to have a much higher barrier than the corresponding isomerization reaction and the β-scission of CH3C(=O)OCH2. Consequently, the rate coefficients for β-scission of CH2C(=O)OCH3 are the smallest among the three reactions and the isomerization followed by decomposition to CH3C(=O) and HCHO is the dominant reaction pathway for CH2C(=O)OCH3. Furthermore, both radicals CH2C(=O)OCH3 and CH3C(=O)OCH2 are predicted to mainly decompose to CH3C(=O) + HCHO rather than to the bimolecular product CH2C(=O) + CH3O. A newly developed MA combustion mechanism, using our theoretical rate coefficients for the MA-related reactions, predicts combustion properties in good agreement with available experimental data.},
doi = {10.1021/acs.jpca.5b08331},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
issn = {1089-5639},
number = 42,
volume = 119,
place = {United States},
year = {2015},
month = {10}
}

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