Adventures on the C3H5O potential energy surface: OH + propyne, OH + allene and related reactions

Zádor, Judit; Miller, James A.

doi:10.1016/j.proci.2014.05.103

Cited by 52 publications

(69 citation statements)

References 39 publications

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“…Modified Arrhenius expressions for the ketene + CH 3 ⇆ acetonyl rate constants in both directions are presented in Table S2 in the Supporting Information. The values calculated here for acetonyl dissociation agree with those generated by Zador and Miller in their study of the allene/propyne + OH reactions within factors of 2–3, with the present results being higher; the agreement is better than a factor of 2 at lower pressures and higher temperatures. We do not compare the a‐/p‐C 3 H 4 + OH → CH 2 CO + CH 3 rate constants in our study with the results by Zador and Miller because we did not consider all possible channels for these reactions, but only those relevant to the reverse CH 2 CO + CH 3 → a‐/p‐C 3 H 4 + OH reaction.…”

Section: Resultssupporting

confidence: 88%

“…This radical intermediate, if stabilized, can participate in bimolecular reactions with other molecules or radicals available or undergo unimolecular dissociation, also preferably back to ketene + CH 3 . The reverse reactions for channel 1, propyne/allene + OH were recently studied by Zador and Miller using a similar UCCSD(T)‐F12/cc‐pVQZ‐f12//M06‐2X/6‐311++G(d,p) level of theory for PES and RRKM–ME for kinetics calculations. The calculated relative energies of the species and transition states common for the two studies agree within few tenths of a kcal/mol.…”

Section: Resultsmentioning

confidence: 99%

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Mechanism and Rate Constants of the CH₃+ CH₂CO Reaction: A Theoretical Study

Semenikhin

Shubina

Savchenkova

et al. 2018

Int J of Chemical Kinetics

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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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Section: Resultssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Mechanism and Rate Constants of the CH₃+ CH₂CO Reaction: A Theoretical Study

Semenikhin

Shubina

Savchenkova

et al. 2018

Int J of Chemical Kinetics

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“…The C 2 H 3 + HO 2 reaction forms CH 2 CHO + OH as well as C 2 H 4 + O 2 , and both the rate constant and the branching fraction are uncertain; we use a rate constant for C 2 H 4 + O 2 obtained from theory by Hua et al . The rate constant for C 2 H 3 + CH 2 O → C 2 H 4 + HCO was drawn from the recent theoretical work of Zador and Miller who studied reactions on the C 3 H 5 O potential energy surface. Ethane is only formed in small quantities, mainly through the sequence C 2 H 2

\overset{+ normalO}{⟶}

CH 2

\overset{+ normalH}{⟶}

CH 3

\overset{+ {CH}_{3}}{⟶}

C 2 H 6 .…”

Section: Resultsmentioning

confidence: 99%

Experimental and Kinetic Modeling Study of C₂H₂ Oxidation at High Pressure

Giménez-López

Rasmussen

Hashemi

et al. 2016

Int J of Chemical Kinetics

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A detailed chemical kinetic model for oxidation of C 2 H 4 in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C 2 H 3 + O 2 reaction was was used to obtain rate coefficients over a wide range of conditions (0.003-100 bar, 200-3000 K). The results indicate that at 60 bar vinyl peroxide, rather than CH 2 O and HCO, is the dominant product.The experiments, involving C 2 H 4 /O 2 mixtures diluted in N 2 , were carried out in a high pressure flow reactor at 600-900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Under the investigated conditions the oxidation pathways for C 2 H 4 are more complex than those prevailing at higher temperatures and lower pressures. The major differences are the importance of the hydroxyethyl (CH 2 CH 2 OH) and 2-hydroperoxyethyl 1 (CH 2 CH 2 OOH) radicals, formed from addition of OH and HO 2 to C 2 H 4 , and vinyl peroxide, formed from C 2 H 3 + O 2 . Hydroxyethyl is oxidized through the peroxide HOCH 2 CH 2 OO (lean conditions) or through ethenol (low O 2 concentration), while 2-hydroperoxyethyl is converted through oxirane. [2][3][4][5][6][7], shock tubes [8][9][10][11][12] and premixed laminar flames [13][14][15][16][17], covering a wide range of stoichiometries and temperatures. Most of the reported work, however, have been carried out at near atmospheric pressure. A few results are available from flow reactor studies at 5-10 bar [6], but despite their relevance for the chemistry in engines, gas turbines, and gas-to-liquid processes, data at high pressures are limited.The objective of the present study is to obtain experimental results for the oxidation of C 2 H 4 at high pressure (60 bar) as functions of temperature (600-900 K) and stoichiometry (lean to fuel-rich) and analyze them in terms of a detailed chemical kinetic model. The oxidation pathways for C 2 H 4 under these conditions are different from those prevailing at higher temperatures and lower pressures and the results of the current work help to extend the validation range for chemical kinetic modeling of C 2 H 4 oxidation. This paper is part of a series investigating the high-pressure, medium temperature oxidation of simple fuels: previously work has been reported for CO/H 2 , CH 4 , and CH 4 /C 2 H 6 mixtures [18,19]. The present kinetic model draws on this work, as well as recent results in tropospheric chemistry. Furthermore, the important reaction of C 2 H 3 with O 2 was characterized from ab initio calculations over a wide range of pressure and temperature. 3 ExperimentalThe experimental setup is a laboratory-scale high pressure laminar flow reactor designed to approximate plug-flow. The setup is described in detail elsewhere [18] and only a brief description is provided here. The system enables well-defined investigations of...

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“…Conformational searches were executed to determine the lowest energy structures and axial and equatorial conformers were accounted for individually (Supplemental Material S5). In addition, relevant parts of the α-tetrahydropyranyl potential energy surface were explored using KinBot [19,20] to determine its unimolecular decomposition pathways. Master Equation calculations were then conducted at the CCSD(T)-F12a/cc-PVDZ//M06-2X/6-311 ++ G * * level of theory at the conditions of the experiments in order to calculate the unimolecular decomposition rate coefficients for α-tetrahydropyranyl using the MESS code [21] .…”

Section: Ab Initio Calculationsmentioning

confidence: 99%

“…Barrier heights for unimolecular reactions on the α-tetrahydropyranyl potential energy surface (PES) were explored using KinBot [19,20] , which found channels leading to linear radicals, ˙ C H 2 ( C H 2 ) 3 CHO (23.2 kcal/mol) or ˙ C H 2 ( C H 2 ) 2 OCH = C H 2 (34.3 kcal/mol), intramolecular hydrogen-transfer products, β-tetrahydropyranyl (34.6 kcal/mol) or γ -tetrahydropyranyl (47.3 kcal/mol), and 3,4-dihydro-2H-pyran + H (35.1 kcal/mol) from loss of hydrogen via C-H bond-scission (S10). The preceding energies listed in parentheses are relative to α-tetrahydropyranyl at the CCSD(T)-F12a/cc-PVDZ//M06-2X/6-311 ++ G * * level of theory.…”

Section: Unimolecular Decomposition Of α-Tetrahydropyranylmentioning

confidence: 99%

Influence of oxygenation in cyclic hydrocarbons on chain-termination reactions from R + O2: tetrahydropyran and cyclohexane

Rotavera

Savee

Antonov

et al. 2017

Proceedings of the Combustion Institute

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Multiplexed photoionization mass spectrometry (MPIMS) is used to determine branching fractions of conjugate alkenes from R + O 2 oxidation reactions for cyclohexane ( c -C 6 H 12 ) and tetrahydropyran ( c -C 5 H 10 O), a lignocellulosic-derived oxygenated biofuel. Because conjugate alkene formation is coincident with the formation of HO 2 , the results reveal the temperature-and pressure-dependent influence of the oxygen heteroatom on chain-termination propensity. The experiments were conducted using Cl-initiated oxidation at 10 and 1520 Torr and from 500 to 700 K, and ab initio calculations of bond energies, saddle point energies, and rate coefficients of unimolecular decomposition of α-tetrahydropyranyl were conducted to complement the experiments.Relative to the initial radical concentration [R] 0 the trend in conjugate alkene branching fraction exhibits monotonic positive temperature dependence in both cyclohexane and tetrahydropyran, except for the latter species at 10 Torr where increasing the temperature to 700 K caused an appreciable decrease. The decrease in the branching fraction with increasing temperature in tetrahydropyran oxidation occurs because ring-opening rates of α-tetrahydropyranyl radicals, enabled by weak C-O bond dissociation energies, exceed rates of O 2 -addition. Ring-opening rate coefficients for α-tetrahydropyranyl, computed from stationary points at the CCSD(T)-F12a/cc-PVDZ//M06-2X/6-311 ++ G * * level of theory, confirm that ring-opening at 700 K is favorable and higher oxygen concentrations are required for O 2 -addition rates to be significant. With increased temperature and lower [O 2 ], α-tetrahydropyranyl radicals preferentially undergo unimolecular decomposition into the linear radical ˙ C H 2 ( C H 2 ) 3 CHO . Conjugate alkene branching fractions measured at 1520 Torr for both cyclohexane and tetrahydropyran followed monotonic positive temperature dependence. The change in the tetrahydropyran trend at 1520 Torr relative to the 10 Torr measurements is ascribed to the increase in oxygen concentration mitigating ring-opening reactions of the initial R radicals.In contrast to the results at higher temperature, where ring-opening of tetrahydropyranyl radicals interrupts R + O 2 chemistry and reduces the formation of conjugate alkenes, branching fractions measured below 700 K were higher in tetrahydropyran compared to cyclohexane at 10 Torr. The difference suggests BRotave@Sandia.gov (B. Rotavera), CATaatj@Sandia.gov (C.A. Taatjes). that the ether group renders chain-termination pathways more-facile. Saddle point energy calculations on the surfaces of equatorial ROO conformers reveal that the barrier height to direct HO 2 formation from α-tetrahydropyranylperoxy is lower by ca. 5 kcal/mol compared to cyclohexylperoxy at the CBS-QB3 level of theory, which facilitates low-temperature chain-termination.

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Adventures on the C3H5O potential energy surface: OH + propyne, OH + allene and related reactions

Cited by 52 publications

References 39 publications

Mechanism and Rate Constants of the CH₃+ CH₂CO Reaction: A Theoretical Study

Mechanism and Rate Constants of the CH₃+ CH₂CO Reaction: A Theoretical Study

Experimental and Kinetic Modeling Study of C₂H₂ Oxidation at High Pressure

Influence of oxygenation in cyclic hydrocarbons on chain-termination reactions from R + O2: tetrahydropyran and cyclohexane

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Adventures on the C3H5O potential energy surface: OH + propyne, OH + allene and related reactions

Cited by 52 publications

References 39 publications

Mechanism and Rate Constants of the CH3+ CH2CO Reaction: A Theoretical Study

Mechanism and Rate Constants of the CH3+ CH2CO Reaction: A Theoretical Study

Experimental and Kinetic Modeling Study of C2H2 Oxidation at High Pressure

Influence of oxygenation in cyclic hydrocarbons on chain-termination reactions from R + O2: tetrahydropyran and cyclohexane

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Mechanism and Rate Constants of the CH₃+ CH₂CO Reaction: A Theoretical Study

Mechanism and Rate Constants of the CH₃+ CH₂CO Reaction: A Theoretical Study

Experimental and Kinetic Modeling Study of C₂H₂ Oxidation at High Pressure