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Title: The multichannel n -propyl + O 2 reaction surface: Definitive theory on a model hydrocarbon oxidation mechanism

Abstract

The n-propyl + O2 reaction is an important model of chain branching reactions in larger combustion systems. In this work, focal point analyses (FPAs) extrapolating to the ab initio limit were performed on the n-propyl + O2 system based on explicit quantum chemical computations with electron correlation treatments through coupled cluster single, double, triple, and perturbative quadruple excitations [CCSDT(Q)] and basis sets up to cc-pV5Z. All reaction species and transition states were fully optimized at the rigorous CCSD(T)/cc-pVTZ level of theory, revealing some substantial differences in comparison to the density functional theory geometries existing in the literature. A mixed Hessian methodology was implemented and benchmarked that essentially makes the computations of CCSD(T)/cc-pVTZ vibrational frequencies feasible and thus provides critical improvements to zero-point vibrational energies for the n-propyl + O2 system. Two key stationary points, n-propylperoxy radical (MIN1) and its concerted elimination transition state (TS1), were located 32.7 kcal mol−1 and 2.4 kcal mol−1 below the reactants, respectively. Two competitive β-hydrogen transfer transition states (TS2 and TS2′) were found separated by only 0.16 kcal mol−1, a fact unrecognized in the current combustion literature. Incorporating TS2′ in master equation (ME) kinetic models might reduce the large discrepancy of 2.5 kcal mol−1 betweenmore » FPA and ME barrier heights for TS2. TS2 exhibits an anomalously large diagonal Born-Oppenheimer correction (ΔDBOC = 1.71 kcal mol−1), which is indicative of a nearby surface crossing and possible nonadiabatic reaction dynamics. The first systematic conformational search of three hydroperoxypropyl (QOOH) intermediates was completed, uncovering a total of 32 rotamers lying within 1.6 kcal mol−1 of their respective lowest-energy minima. Our definitive energetics for stationary points on the n-propyl + O2 potential energy surface provide key benchmarks for future studies of hydrocarbon oxidation.« less

Authors:
 [1];  [1];  [2];  [1];  [1]
  1. Center for Computational Chemistry and Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
  2. College of Chemistry &, Pharmacy, Northwest A&,F University, Yangling, Shaanxi 712100, People’s Republic of China
Publication Date:
Research Org.:
Univ. of Georgia, Athens, GA (United States); Univ. of California, Oakland, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1540155
Alternate Identifier(s):
OSTI ID: 1423507
Grant/Contract Number:  
SC0018412; AC02-05CH11231; SC0015512
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 148; Journal Issue: 9; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
Chemistry; Physics

Citation Formats

Bartlett, Marcus A., Liang, Tao, Pu, Liang, Schaefer, Henry F., and Allen, Wesley D. The multichannel n -propyl + O 2 reaction surface: Definitive theory on a model hydrocarbon oxidation mechanism. United States: N. p., 2018. Web. doi:10.1063/1.5017305.
Bartlett, Marcus A., Liang, Tao, Pu, Liang, Schaefer, Henry F., & Allen, Wesley D. The multichannel n -propyl + O 2 reaction surface: Definitive theory on a model hydrocarbon oxidation mechanism. United States. doi:10.1063/1.5017305.
Bartlett, Marcus A., Liang, Tao, Pu, Liang, Schaefer, Henry F., and Allen, Wesley D. Wed . "The multichannel n -propyl + O 2 reaction surface: Definitive theory on a model hydrocarbon oxidation mechanism". United States. doi:10.1063/1.5017305. https://www.osti.gov/servlets/purl/1540155.
@article{osti_1540155,
title = {The multichannel n -propyl + O 2 reaction surface: Definitive theory on a model hydrocarbon oxidation mechanism},
author = {Bartlett, Marcus A. and Liang, Tao and Pu, Liang and Schaefer, Henry F. and Allen, Wesley D.},
abstractNote = {The n-propyl + O2 reaction is an important model of chain branching reactions in larger combustion systems. In this work, focal point analyses (FPAs) extrapolating to the ab initio limit were performed on the n-propyl + O2 system based on explicit quantum chemical computations with electron correlation treatments through coupled cluster single, double, triple, and perturbative quadruple excitations [CCSDT(Q)] and basis sets up to cc-pV5Z. All reaction species and transition states were fully optimized at the rigorous CCSD(T)/cc-pVTZ level of theory, revealing some substantial differences in comparison to the density functional theory geometries existing in the literature. A mixed Hessian methodology was implemented and benchmarked that essentially makes the computations of CCSD(T)/cc-pVTZ vibrational frequencies feasible and thus provides critical improvements to zero-point vibrational energies for the n-propyl + O2 system. Two key stationary points, n-propylperoxy radical (MIN1) and its concerted elimination transition state (TS1), were located 32.7 kcal mol−1 and 2.4 kcal mol−1 below the reactants, respectively. Two competitive β-hydrogen transfer transition states (TS2 and TS2′) were found separated by only 0.16 kcal mol−1, a fact unrecognized in the current combustion literature. Incorporating TS2′ in master equation (ME) kinetic models might reduce the large discrepancy of 2.5 kcal mol−1 between FPA and ME barrier heights for TS2. TS2 exhibits an anomalously large diagonal Born-Oppenheimer correction (ΔDBOC = 1.71 kcal mol−1), which is indicative of a nearby surface crossing and possible nonadiabatic reaction dynamics. The first systematic conformational search of three hydroperoxypropyl (QOOH) intermediates was completed, uncovering a total of 32 rotamers lying within 1.6 kcal mol−1 of their respective lowest-energy minima. Our definitive energetics for stationary points on the n-propyl + O2 potential energy surface provide key benchmarks for future studies of hydrocarbon oxidation.},
doi = {10.1063/1.5017305},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 9,
volume = 148,
place = {United States},
year = {2018},
month = {3}
}

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