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

Savchenkova, Anna S. (författare)
Samara National Research University
Semenikhin, Alexander S. (författare)
Samara National Research University
Chechet, Ivan V. (författare)
Samara National Research University
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Matveev, Sergey G. (författare)
Samara National Research University
Konnov, Alexander A. (författare)
Lund University,Lunds universitet,Förbränningsfysik,Fysiska institutionen,Institutioner vid LTH,Lunds Tekniska Högskola,Combustion Physics,Department of Physics,Departments at LTH,Faculty of Engineering, LTH
Mebel, Alexander M. (författare)
Samara National Research University,Florida International University
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 (creator_code:org_t)
2018-10-09
2019
Engelska.
Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 40:2, s. 387-399
  • Tidskriftsartikel (refereegranskat)
Abstract Ämnesord
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  • 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.

Ämnesord

NATURVETENSKAP  -- Kemi -- Analytisk kemi (hsv//swe)
NATURAL SCIENCES  -- Chemical Sciences -- Analytical Chemistry (hsv//eng)

Nyckelord

ketene
methylene
potential energy surface
reaction rate constant
triplet-singlet crossing MSX

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