Symmetry numbers and chemical reaction rates

Fernández‐Ramos, Antonio; Ellingson, Benjamin A.; Meana-Pañeda, Rubén; Marques, Jorge M. C.; Truhlar, Donald G.

doi:10.1007/s00214-007-0328-0

Cited by 390 publications

(381 citation statements)

References 20 publications

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“…26,27 Table 3 is a summary of the global symmetry values and the number of single events of the elementary steps of chain growth. It should be added here that FT synthesis essentially only produces linear chains.…”

Section: For a Bimolecular Elementary Reactionmentioning

confidence: 99%

Advanced fundamental modeling of the kinetics of Fischer–Tropsch synthesis

Zhou

Froment²,

Yang

et al. 2016

AIChE Journal

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The kinetic modeling of Fischer-Tropsch Synthesis on an iron catalyst starting from experimental data collected in a spinning basket reactor and proceeding through the Single Event approach to limit the number of independent parameters is reported. The elementary steps are based on the carbide mechanism with hydrogen assisted CO insertion and CH 2 as the growth monomer. The evolution with the chain length of alkane-, alkene-, and alcohol-selectivities in the synthesis product and their exponential-like behavior is fundamentally generated by accounting for the effect of the structure of reactants and transition state intermediates on the rate coefficients. The olefin readsorption is included in the model but its influence on the product distribution is found to be negligible.

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Section: For a Bimolecular Elementary Reactionmentioning

confidence: 99%

Advanced fundamental modeling of the kinetics of Fischer–Tropsch synthesis

Zhou

Froment²,

Yang

et al. 2016

AIChE Journal

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“…The calculated rate constants also show that the rectangular barrier approximation currently used in models inaccurately estimates kinetic isotope effects for the title reaction by approximately two orders of magnitude. constants In the gas phase, rotational motion is not restricted, and moreover the symmetry of the reactant and transition states needs to be taken into account in the calculation of the rate constants (Fernández-Ramos et al 2007). The symmetry factor used here is 12, resulting from the pointgroups T d for the methane molecule, C ∞V for OH, and C s for the eclipsed and staggered instanton configurations.…”

Section: Discussionmentioning

confidence: 99%

“…On the surface, rotational motions are restricted and therefore the rotational partition function is kept constant, that is, frozen-out. However, the rotational symmetry factor (Fernández-Ramos et al 2007) of 3 between the C 3v -symmetric Van der Waals complex and the transition state or instanton is taken into account. Finally, another effect of the surface can be on the activation barrier of the reaction.…”

Section: Computational Detailsmentioning

confidence: 99%

Importance of tunneling in H-abstraction reactions by OH radicals

Lamberts

Fedoseev

Kästner

et al. 2017

A&A

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We present a combined experimental and theoretical study focussing on the quantum tunneling of atoms in the reaction between CH 4 and OH. The importance of this reaction pathway is derived by investigating isotope substituted analogs. Quantitative reaction rates needed for astrochemical models at low temperature are currently unavailable both in the solid state and in the gas phase. Here, we study tunneling effects upon hydrogen abstraction in CH 4 + OH by focusing on two reactions: CH 4 + OD − − → CH 3 + HDO and CD 4 + OH − − → CD 3 + HDO. The experimental study shows that the solid-state reaction rate R CH 4 +OD is higher than R CD 4 +OH at 15 K. Experimental results are accompanied by calculations of the corresponding unimolecular and bimolecular reaction rate constants using instanton theory taking into account surface effects. For the work presented here, the unimolecular reactions are particularly interesting as these provide insight into reactions following a Langmuir-Hinshelwood process. The resulting ratio of the rate constants shows that the H abstraction (k CH 4 +OD ) is approximately ten times faster than D-abstraction (k CD 4 +OH ) at 65 K. We conclude that tunneling is involved at low temperatures in the abstraction reactions studied here. The unimolecular rate constants can be used by the modeling community as a first approach to describe OH-mediated abstraction reactions in the solid phase. For this reason we provide fits of our calculated rate constants that allow the inclusion of these reactions in models in a straightforward fashion.

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“…According to the methodology detailed in Ref. [38], a reaction symmetry number of 6 was used to account for the number of symmetrically equivalent reaction paths. The low-frequency modes correspond to rotations of the -CH 3 groups in the reactants and transition states are treated as hindered rotors.…”

Section: Rate Constantsmentioning

confidence: 99%

Kinetics of the hydrogen abstraction ·C2H5 + alkane → C2H6 + alkyl reaction class: an application of the reaction class transition state theory

et al. 2013

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This paper presents an application of the reaction class transition state theory (RC-TST) to predict thermal rate constants for hydrogen abstraction reactions at alkane by the ÁC 2 H 5 radical on-the-fly. The linear energy relationship (LER), developed for acyclic alkanes, was also proven to hold for cyclic alkanes. We have derived all RC-TST parameters from rate constants of 19 representative reactions, coupling with LER and the barrier height grouping (BHG) approach. Both the RC-TST/LER, where only reaction energy is needed, and the RC-TST/BHG, where no other information is needed, can predict rate constants for any reaction in this reaction class with satisfactory accuracy for combustion modeling. Our analysis indicates that less than 50 % systematic errors on the average exist in the predicted rate constants using either the RC-TST/LER or RC-TST/BHG method, while in comparison with explicit rate calculations, the differences are within a factor of 2 on the average. The results also show that the RC-TST method is not sensitive to the choice of density functional theory used.

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Symmetry numbers and chemical reaction rates

Cited by 390 publications

References 20 publications

Advanced fundamental modeling of the kinetics of Fischer–Tropsch synthesis

Advanced fundamental modeling of the kinetics of Fischer–Tropsch synthesis

Importance of tunneling in H-abstraction reactions by OH radicals

Kinetics of the hydrogen abstraction ·C2H5 + alkane → C2H6 + alkyl reaction class: an application of the reaction class transition state theory

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