Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states : A theoretical study
(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
- Savchenkova, Anna S. ; Semenikhin, Alexander S. ; Chechet, Ivan V. ; Matveev, Sergey G. ; Konnov, Alexander A. LU and Mebel, Alexander M.
- organization
- publishing date
- 2019-01-15
- 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 Inc.
- external identifiers
-
- pmid:30299558
- 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
- 2024-07-08 23:37:34
@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}}, keywords = {{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 Inc.}}, 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}}, doi = {{10.1002/jcc.25613}}, volume = {{40}}, year = {{2019}}, }