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Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states : A theoretical study

Savchenkova, Anna S.; Semenikhin, Alexander S.; Chechet, Ivan V.; Matveev, Sergey G.; Konnov, Alexander A. LU and Mebel, Alexander M. (2019) In Journal of Computational Chemistry 40(2). p.387-399
Abstract

Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH2 with ketene CH2CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH3 and C2H4 + CO... (More)

Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH2 with ketene CH2CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH3 and C2H4 + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C2H4 + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH2COCH2 intermediate or along the pathway of CO elimination from the initial CH2CH2CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C2H4 + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH3CHCO and cyclic CH2COCH2 intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
ketene, methylene, potential energy surface, reaction rate constant, triplet-singlet crossing MSX
in
Journal of Computational Chemistry
volume
40
issue
2
pages
387 - 399
publisher
John Wiley & Sons
external identifiers
  • scopus:85054561760
ISSN
0192-8651
DOI
10.1002/jcc.25613
language
English
LU publication?
yes
id
60696aa2-bbf9-4b2a-835e-77cfbceb30dd
date added to LUP
2018-11-13 11:00:06
date last changed
2019-01-15 04:30:00
@article{60696aa2-bbf9-4b2a-835e-77cfbceb30dd,
  abstract     = {<p>Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH<sub>2</sub> with ketene CH<sub>2</sub>CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH<sub>3</sub> and C<sub>2</sub>H<sub>4</sub> + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C<sub>2</sub>H<sub>4</sub> + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH<sub>2</sub>COCH<sub>2</sub> intermediate or along the pathway of CO elimination from the initial CH<sub>2</sub>CH<sub>2</sub>CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C<sub>2</sub>H<sub>4</sub> + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH<sub>3</sub>CHCO and cyclic CH<sub>2</sub>COCH<sub>2</sub> intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion.</p>},
  author       = {Savchenkova, Anna S. and Semenikhin, Alexander S. and Chechet, Ivan V. and Matveev, Sergey G. and Konnov, Alexander A. and Mebel, Alexander M.},
  issn         = {0192-8651},
  keyword      = {ketene,methylene,potential energy surface,reaction rate constant,triplet-singlet crossing MSX},
  language     = {eng},
  month        = {01},
  number       = {2},
  pages        = {387--399},
  publisher    = {John Wiley & Sons},
  series       = {Journal of Computational Chemistry},
  title        = {Mechanism and rate constants of the CH<sub>2</sub> + CH<sub>2</sub>CO reactions in triplet and singlet states : A theoretical study},
  url          = {http://dx.doi.org/10.1002/jcc.25613},
  volume       = {40},
  year         = {2019},
}