| 1. |
- Savchenkova, Anna S., et al.
(författare)
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Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states : A theoretical study
- 2019
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Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 40:2, s. 387-399
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Tidskriftsartikel (refereegranskat)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 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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| 2. |
- Savchenkova, Anna S., et al.
(författare)
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Revisiting diacetyl and acetic acid flames : The role of the ketene + OH reaction
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 218, s. 28-41
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the reaction of ketene with hydroxyl radical has been studied by ab initio CCSD(T)-F12/cc-pVQZ-F12//B3LYP/6-311G(d,p) calculations of the potential energy surface. Temperature- and pressure-dependent reaction rate constants have been computed using the RRKM-Master Equation and transition state theory methods in the temperature range of 300–3000 K and in the pressure range of 0.01–100 atm. Three main channels have been analyzed: through direct abstraction of H atoms or starting with OH addition to the terminal carbon and to the central carbon atoms. Major products identified agree with the recent theoretical studies, however, significant difference was found with the rate constants derived by Xu et al. [13] and Cavallotti et al. [11]. To investigate the impact of the choice of reactions between CH2CO and OH radicals on the predicted burning velocities of the flames sensitive to ketene chemistry, namely diacetyl and acetic acid flames, a detailed kinetic mechanism was updated with pertinent reactions suggested in the literature. Then the rate constants of four most important product channels of reaction CH2CO + OH forming HCCO + H2O, CH2OH + CO, CH3 + CO2 and CH2COOH from the present and from the recent theoretical studies were tested. Good agreement with the burning velocities of diacetyl + air flames was found for the present model, while the expressions from the literature underestimate them. On the contrary, any combination of the rate constants of reactions between ketene and hydroxyl radical overpredicts burning velocities of acetic acid + air flames, which strongly indicates that the kinetic model of acetic acid is most probably incomplete and requires consideration of additional reactions.
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| 3. |
- Hayes, Michael, et al.
(författare)
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An improved potential energy surface for the F+H2 reaction
- 2005
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 308:3 Special Issue, s. 259-266
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Tidskriftsartikel (refereegranskat)abstract
- A new ground state potential energy surface has been developed for the F+H2 reaction. Using the UCCSD(T) method, ab initio calculations were performed for 786 geometries located mainly in the exit channel of the reaction. The new data was used to correct exit channel errors that have become apparent in the potential energy surface of Stark and Werner [J. Chem. Phys. 104 (1996) 6515]. While the entrance channel and saddlepoint properties of the Stark–Werner surface are unchanged on the new potential, the exit channel behavior is more satisfactory. The exothermicity on the new surface is much closer to the experimental value. The new surface also greatly diminishes the exit channel van der Waals well that was too pronounced on the Stark–Werner surface. Several preliminary dynamical scattering calculations were carried out using the new surface for total angular momentum equal to zero for F+H2 and F+HD. It is found that gross features of the reaction dynamics are quite similar to those predicted by the Stark–Werner surface, in particular the reactive resonance for F+HD and F+H2 survive. However, the most of the exit channel van der Waals resonances disappear on the new surface. It is predicted that the differential cross-sections at low collision energy for the F+H2 reaction may be drastically modified from the predictions based on the Stark–Werner surface.
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