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| 2. |
- Savchenkova, A. S., et al.
(författare)
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Formation of Pyridyl Radicals by Hydrogen Atom Abstraction : Theoretical Study
- 2023
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Ingår i: Combustion, Explosion and Shock Waves. - 0010-5082. ; 59:2, s. 125-128
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Specific features of the pyridine structure make it a convenient model system to describe coal combustion; however, the main attention of researchers has been paid to the formation of the ortho-pyridyl, whereas the formation of meta- and para-pyridyls has been yet poorly studied. The rate constants of the formation of three pyridyl radicals originating from pyridine by hydrogen atom abstraction by another hydrogen atom are compared. The geometry of the reactants is optimized within the framework of the density functional theory with subsequent refinement of single-point energies by the ab initioG3(MP2,CC) hybrid method. The calculations show that the formation of ortho-pyridyl is more favorable, though the formation and further transformations of all three radicals should be taken into account for a detailed description of the coal combustion process.
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| 3. |
- Semenikhin, A. S., et al.
(författare)
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Mechanism and Rate Constants of the CH3+ CH2CO Reaction : A Theoretical Study
- 2018
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Ingår i: International Journal of Chemical Kinetics. - : Wiley. - 0538-8066. ; 50:4, s. 273-284
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the reaction of ketene with methyl radical has been studied by ab initio CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations of the potential energy surface. Temperature- and pressure-dependent reaction rate constants have been computed using the Rice-Ramsperger-Kassel-Marcus (RRKM)-Master Equation and transition state theory methods. Three main channels have been shown to dominate the reaction; the formation of the collisionally stabilized CH3COCH2 radical and the production of the C2H5 + CO and HCCO + CH4 bimolecular products. Relative contributions of the CH3COCH2, C2H5 + CO, and HCCO + CH4 channels strongly depend on the reaction conditions; the formation of thermalized CH3COCH2 is favored at low temperatures and high pressures, HCCO + CH4 is dominant at high temperatures, whereas the yield of C2H5 + CO peaks at intermediate temperatures around 1000 K. The C2H5 + CO channel is favored by a decrease in pressure but remains the second most important reaction pathway after HCCO + CH4 under typical flame conditions. The calculated rate constants at different pressures are proposed for kinetic modeling of ketene reactions in combustion in the form of modified Arrhenius expressions. Only rate constant to form CH3COCH2 depends on pressure, whereas those to produce C2H5 + CO and HCCO + CH4 appeared to be pressure independent.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Veinger, A.I., et al.
(författare)
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Low temperature transformation from antiferromagnetic to ferromagnetic order in impurity system Ge:As near the insulator-metal phase transition
- 2014
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Ingår i: 15th International conference on transport in interacting disordered systems (TIDS15). - : American Institute of Physics (AIP). - 9780735412460 ; , s. 129-134
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Konferensbidrag (refereegranskat)abstract
- The low-temperature transformation from antiparallel to parallel spin orientation in a nonmagnetic compensated system Ge:As semiconductor near the metal-insulator phase transition has been experimentally observed. This effect is manifested in the temperature dependences of the impurity magnetic susceptibility obtained by integration of the spin resonance absorption line. These dependences show that the spin density falls in the medium temperature range (10-100 K) and grows at low temperatures. The effect is confirmed by the specific temperature features of the g-factor and inverse magnetic susceptibility. As the relative content of a compensating impurity (gallium) is made lower than 0.7, the transition temperature begins to decrease and, at a degree of compensation < 0.3, falls outside the temperature range under study (i.e., below 2 K). © 2014 AIP Publishing LLC.
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| 7. |
- Veinger, A. I., et al.
(författare)
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Low-temperature variation of magnetic order in a nonmagnetic n-Ge:As semiconductor in the vicinity of the metal-insulator phase transition
- 2013
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Ingår i: Journal of Experimental and Theoretical Physics. - : MAIK Nauka/Interperiodica/Springer. - 1063-7761 .- 1090-6509. ; 116:5, s. 796-799
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of the low-temperature transition from antiferro- to ferromagnetic ordering of impurity spins in a nonmagnetic compensated n-Ge:As semiconductor near the metal-insulator phase transformation has been experimentally observed. The effect is manifested by rather sharp changes in the spin density and g-factor in the electron spin resonance spectra. As the relative content of a compensating impurity (gallium) is reduced below 0.7, the transition temperature begins to decrease and, at a degree of compensation below 0.3, drops below the studied temperature range (i.e., below 2 K).
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