Exploring the stereodynamics and microscopic mechanism of the O(3P) + CH4, CD4→ OH + CH3, OD + CD3 combustion reactions

Martı́nez, Rodrigo; Enríquez, Pedro A.; Puyuelo, P.; González, Miguel

doi:10.1016/j.chemphys.2015.08.019

Cited by 8 publications

(8 citation statements)

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“…This will increase the probability of the O( 3 P) atom approach close to parallel to the H−C bond axis, which is known to be the strongly preferred geometry from experiments and ab initio potentials for gas-phase reactions of related smaller alkanes. 84,117 It will also reduce overshadowing of the reactive −CH 2 − positions by the unreactive terminal methyl groups. These effects together might explain discrepancy (A).…”

Section: ■ Discussionmentioning

confidence: 99%

“…It is believable from inspection of MD snapshots such as those in Figures –, as supported by the limited analyses of chain orientation for different chain lengths that has been carried out, , that the outer ends of longer chains tend to lie more parallel to the surface (and perpendicular to the surface normal) than shorter chains. This will increase the probability of the O( 3 P) atom approach close to parallel to the H–C bond axis, which is known to be the strongly preferred geometry from experiments and ab initio potentials for gas-phase reactions of related smaller alkanes. , It will also reduce overshadowing of the reactive −CH 2 – positions by the unreactive terminal methyl groups. These effects together might explain discrepancy (A).…”

Section: Discussionmentioning

confidence: 99%

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Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

et al. 2022

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The gas–liquid interface of ionic liquids (ILs) is critically important in many applications, for example, in supported IL phase (SILP) catalysis. Methods to investigate the interfacial structure in these systems will allow their performance to be improved in a rational way. In this study, reactive-atom scattering (RAS), surface tension measurements, and molecular dynamics (MD) simulations were used to study the vacuum interface of mixtures of partially fluorinated and normal alkyl ILs. The underlying aim was to understand whether fluorinated IL ions could be used as additives to modify the surface structure of one of the most widely used families of alkyl ILs. The series of ILs 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C n mim][Tf 2 N]) with n = 4–12 were mixed with a fixed-length, semiperfluorinated analogue (1 H ,1 H ,2 H ,2 H -perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 8 mimF 13 ][Tf 2 N]), forming [C n mim] (1– x ) [C 8 mimF 13 ] x [Tf 2 N] mixtures, where x is the bulk mole fraction of the fluorinated component. The RAS-LIF method combined O-atom projectiles with laser-induced fluorescence (LIF) detection of the product OH as a measure of surface exposure of the alkyl chains. For [C 8 mim] (1– x ) [C 8 mimF 13 ] x [Tf 2 N] mixtures, RAS-LIF OH yields are below those expected from stoichiometry. There are quantitatively consistent negative deviations from linearity of the surface tension. Both results imply that the lower-surface-tension fluoroalkyl material dominates the surface. A similar deficit is found for alkyl chain lengths n = 4, 6, 8, and 12 and for all (nonzero) x investigated by RAS-LIF. Accessible-surface-area (ASA) analyses of the MD simulations for [C n mim] (1– x ) [C 8 mimF 13 ] x [Tf 2 N] mixtures qualitatively reproduce the same primary effect of fluoro-chain predominance of the surface over most of the range of n . However, there are significant quantitative discrepancies between MD ASA predictions and experiment relating to the strength of any n -dependence of the relative alkyl coverage at fixed x , and on the x -dependence at fixed ...

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Section: ■ Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

et al. 2022

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“…Full dimensional quasiclassical trajectory method is also widely used for the title reaction, it is an important complement to the reduced dimensional quantum dynamical calculation. Many important conclusions − have been drawn. Varandas et al showed that the topology of the entrance channel had strong implications on the dynamics of the title reaction.…”

Section: Introductionmentioning

confidence: 99%

Thermal Rate Constants for the O(³P) + CH₄→ OH + CH₃Reaction: The Effects of Quantum Tunneling and Potential Energy Barrier Shape

Zhao

2016

J. Phys. Chem. A

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The rate constants and kinetic isotope effects for the O(P) + CH reaction have been investigated with the quantum instanton method in full dimensionality. The calculated rate constants are in good agreement with the experimental values above 400 K, below which the measured values are scattered. Compared to other theoretical approaches, the quantum instanton method predicts the largest quantum tunneling effect, so it gives the largest rate constants at low temperatures. The calculated kinetic isotope effects are always much larger than 1 and increase with decreasing temperature, due to the zero-point energy and quantum tunneling. Our calculations on different potential energy surfaces demonstrate that the potential energy barrier shape dominates the magnitude of quantum tunneling and has a great effect on the kinetic isotope effect.

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“…Methane is the main component of natural gas, and is stored in not only various minerals − but also the atmosphere as the most abundant hydrocarbon. , Consequently, it is one of the most important atmospheric species. The reactions of ground-state oxygen with hydrocarbons are key initial steps and of significant importance in the combustion processes. − However, even the reactions of O atom with the simplest hydrocarbon molecule are not well understood. It is commonly presumed that the first step is the hydrogen-abstraction by O( 3 P) to generate a significant concentration of CH 3 in flames, which could be oxidized to CO and CO 2 in subsequent combustion steps.…”

Section: Introductionmentioning

confidence: 99%

“…It is commonly presumed that the first step is the hydrogen-abstraction by O( 3 P) to generate a significant concentration of CH 3 in flames, which could be oxidized to CO and CO 2 in subsequent combustion steps. The slightly endothermic reaction O( 3 P) + CH 4 (X 1 A 1 ) → OH(X 2 Π) + CH 3 (X 2 A 2 ″ ) is a prototype one for detailed investigations of the hydrocarbon combustion. − Thus, the topic of this hydrogen-abstraction by O( 3 P) has attracted considerable interest, both from experimental and theoretical perspectives. − …”

Section: Introductionmentioning

confidence: 99%

Mechanism and Kinetics of Methane Combustion, Part I: Thermal Rate Constants for Hydrogen-Abstraction Reaction of CH₄ + O(³P)

2017

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The mechanism and kinetics of gas-phase hydrogen-abstraction by the O(P) from methane are investigated using ab initio calculations and dynamical methods. Not only are the electronic structure properties including the optimized geometries, relative energies, and vibrational frequencies of all the stationary points obtained from state-averaged complete active space self-consistent field calculations, but also the single-point energies for all points on the intrinsic reaction coordinate are evaluated using the internally contracted multireference configuration interaction approach with modified optimized cc-pCVDZ basis sets. Our calculations give a fairly accurate description of the regions around the A″ transition state in the O(P) attacking a near-collinear H-CH direction with a barrier height of 12.53 kcal/mol, which is lower than those reported before. Subsequently, thermal rate constants for this hydrogen-abstraction are calculated using the canonical unified statistical theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in agreement with experiments. The present work reveals the reaction mechanism of hydrogen-abstraction by the O(P) from methane, and it is helpful for the understanding of methane combustion.

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Exploring the stereodynamics and microscopic mechanism of the O(3P) + CH4, CD4→ OH + CH3, OD + CD3 combustion reactions

Cited by 8 publications

References 44 publications

Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

Thermal Rate Constants for the O(³P) + CH₄→ OH + CH₃Reaction: The Effects of Quantum Tunneling and Potential Energy Barrier Shape

Mechanism and Kinetics of Methane Combustion, Part I: Thermal Rate Constants for Hydrogen-Abstraction Reaction of CH₄ + O(³P)

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Exploring the stereodynamics and microscopic mechanism of the O(3P) + CH4, CD4→ OH + CH3, OD + CD3 combustion reactions

Cited by 8 publications

References 44 publications

Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

Thermal Rate Constants for the O(3P) + CH4→ OH + CH3Reaction: The Effects of Quantum Tunneling and Potential Energy Barrier Shape

Mechanism and Kinetics of Methane Combustion, Part I: Thermal Rate Constants for Hydrogen-Abstraction Reaction of CH4 + O(3P)

Contact Info

Product

Resources

About

Thermal Rate Constants for the O(³P) + CH₄→ OH + CH₃Reaction: The Effects of Quantum Tunneling and Potential Energy Barrier Shape

Mechanism and Kinetics of Methane Combustion, Part I: Thermal Rate Constants for Hydrogen-Abstraction Reaction of CH₄ + O(³P)