Low-Temperature Rate Coefficients of C2H with CH4 and CD4 from 154 to 359 K

Opansky, Brian J.; Leone, Stephen R.

doi:10.1021/jp9532677

Cited by 57 publications

(60 citation statements)

References 19 publications

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“…67 We used experimental activation barriers obtained from rate-vs-temperature data over a temperature range of about 150 K -350 K for which the simple Arrhenius form was suitable and for which reaction rates were available. 35,36,[68][69][70][71][72] It must be stressed that these experimentally deduced activation barriers depend on the temperature range used for the Arrhenius fit, 70 and that this complicates a direct comparison with reaction barriers computed quantum mechanically.…”

Section: Theoretical Methodologymentioning

confidence: 99%

High-Level ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems

et al. 2006

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Symmetric and non-symmetric hydrogen abstraction reactions are studied using stateof-the-art ab initio electronic structure methods. Second-order Møller-Plesset perturbation theory (MP2) and the coupled-cluster singles, doubles and perturbative triples [CCSD(T)] methods with large correlation consistent basis sets (cc-pVXZ, where X = D,T,Q) are used in determining the transition-state geometries, activation barriers, and thermodynamic properties of several representative hydrogen abstraction reactions. The importance of basis set, electron correlation, and choice of zeroth-order reference wavefunction in the accurate prediction of activation barriers and reaction enthalpies are also investigated. The ethynyl radical (·CCH), which has a very high affinity for hydrogen atoms, is studied as a prototype hydrogen abstraction agent. Our high-level quantum mechanical computations indicate that hydrogen abstraction using the ethynyl radical has an activation energy of less than 3 kcal mol −1 for * To whom correspondence should be addressed. E-mail addresses: sherrill@gatech.edu; merkle@cc.gatech.edu; rfreitas@rfreitas.com 1 hydrogens bonded to an sp 2 or sp 3 carbon. These low activation barriers further corroborate previous studies suggesting that ethynyl-type radicals would make good tooltips for abstracting hydrogens from diamondoid surfaces during mechanosynthesis. Modeling the diamond C(111) surface with isobutane and treating the ethynyl radical as a tooltip, hydrogen abstraction in this reaction is predicted to be barrierless.

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Section: Theoretical Methodologymentioning

confidence: 99%

High-Level ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems

et al. 2006

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“…8,9 Experiments are carried out in a variabletemperature transverse flow cell. The 2.5 cm diameter 100 cm long flow cell is made of quartz and is surrounded by an insulated outer jacket.…”

Section: Methodsmentioning

confidence: 99%

“…Using a reported cross section of 1.35 × 10 -19 cm -2 and a quantum yield of 0.26, we estimate an upper limit for [C 2 H] to be 4 × 10 11 molecules cm -3 . 20 The transient ethynyl concentration is probed by a single-mode F-center laser operating at 3593.68 cm -1 , which corresponds to the Q 11 (9) line of the A 2 Π-X 2 Σ + (000) transition. 21 The longitudinal mode structure of the F-center laser is monitored with a scanning Fabry-Perot spectrum analyzer.…”

Section: Methodsmentioning

confidence: 99%

Low-Temperature Rate Coefficients for Reactions of the Ethynyl Radical (C₂H) with C₃H₄ Isomers Methylacetylene and Allene

Hoobler

Leone

1999

J. Phys. Chem. A

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Low-temperature rate coefficients for the reactions C 2 H + C 3 H 4 f products [C 3 H 4 ) methylacetylene (propyne) CH 3 CCH and allene (propadiene) CH 2 CCH 2 ] are measured over the temperature range of 155-298 K. Absolute rate constants are determined using laser photolysis and transient infrared absorption spectroscopy. Both reactions are fast, approaching the kinetic limit and have either no temperature dependence or a slight negative temperature dependence. Over the experimental temperature range, the rate constants are fit to the following Arrhenius expressions: k CH 3 CCH ) (1.6 ( 0.4) × 10 -10 exp[(71 ( 50)/T] cm 3 molecule -1 s -1 and k CH 2 CCH 2 ) (1.3 ( 0.6) × 10 -10 exp[(103 ( 136)/T] cm 3 molecule -1 s -1 . The corresponding rate constants at 298 K are k CH 3 CCH ) (1.9 ( 0.3) × 10 -10 cm 3 molecule -1 s -1 and k CH 2 CCH 2 ) (1.7 ( 0.3) × 10 -10 cm 3 molecule -1 s -1 . These measurements provide new reaction rate coefficients for the ethynyl radical, C 2 H, with C 3 H 4 unsaturated hydrocarbons. These are necessary to extend current photochemical models of Jupiter, Saturn, and its satellite Titan.

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“…There have been a number of laboratory studies of these radical-molecule reactions [14]. More recently, there have been studies at low temperatures appropriate for outer planet and satellite atmospheres [15,16]. For these reactions, there is usually a significant temperature dependence of the rate constant.…”

Section: Introductionmentioning

confidence: 99%

Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K

Thorn

Payne

Chillier

et al. 2000

Int. J. Chem. Kinet.

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The total rate constant k 1 has been determined at P ϭ 1 Torr nominal pressure (He) and at T ϭ 298 K for the vinyl-methyl cross-radical reaction: (1) CH 3 ϩ C 2 H 3 : Products. The measurements were performed in a discharge flow system coupled with collision-free sampling to a mass spectrometer operated at low electron energies. Vinyl and methyl radicals were generated by the reactions of F with C 2 H 4 and CH 4 , respectively. The kinetic studies were performed by monitoring the decay of C 2 H 3 with methyl in excess, 6 Ͻ [CH 3 ] 0 / [C 2 H 3 ] 0 Ͻ 21. The overall rate coefficient was determined to be k 1 (298 K) ϭ (1.02 Ϯ 0.53) ϫ 10 Ϫ10 cm 3 molecule Ϫ1 s Ϫ1 with the quoted uncertainty representing total errors. Numerical modeling was required to correct for secondary vinyl consumption by reactions such as C 2 H 3 ϩ H and C 2 H 3 ϩ C 2 H 3 . The present result for k 1 at T ϭ 298 K is compared to two previous studies at high pressure (100-300 Torr He) and to a very recent study at low pressure (0.9-3.7 Torr He).Comparison is also made with the rate constant for the similar reaction CH 3 ϩ C 2 H 5 and with a value for k 1 estimated by the geometric mean rule employing values for k(CH 3 ϩ CH 3 ) and k(C 2 H 3 ϩ C 2 H 3 ). Qualitative product studies at T ϭ 298 K and 200 K indicated formation of C 3 H 6 , C 2 H 2 , and C 3 H 5 as products of the combination-stabilization, disproportionation, and combination-decomposition channels, respectively, of the CH 3 ϩ C 2 H 3 reaction. We also observed the secondary C 4 H 8 product of the subsequent reaction of C 3 H 5 with excess CH 3 ; this observation provides convincing evidence for the combination-decomposition channel yielding C 3 H 5 ϩ H. RRKM calculations with helium as the deactivator support the present and very recent experimental observations that allylic C-H bond rupture is an important path in the combination reaction. The pressure and temperature dependencies of the branching fractions are also predicted. . Reaction rate constants and product channel information are required for all such models that attempt to account quantitatively for the observed atmospheric composition and structure. Hydrocarbon photochemistry is initiated by the photodissociation of methane in the upper

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Low-Temperature Rate Coefficients of C₂H with CH₄ and CD₄ from 154 to 359 K

Cited by 57 publications

References 19 publications

High-Level ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems

High-Level ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems

Low-Temperature Rate Coefficients for Reactions of the Ethynyl Radical (C₂H) with C₃H₄ Isomers Methylacetylene and Allene

Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K

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Low-Temperature Rate Coefficients of C2H with CH4 and CD4 from 154 to 359 K

Cited by 57 publications

References 19 publications

High-Level ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems

High-Level ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems

Low-Temperature Rate Coefficients for Reactions of the Ethynyl Radical (C2H) with C3H4 Isomers Methylacetylene and Allene

Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K

Contact Info

Product

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Low-Temperature Rate Coefficients of C₂H with CH₄ and CD₄ from 154 to 359 K

Low-Temperature Rate Coefficients for Reactions of the Ethynyl Radical (C₂H) with C₃H₄ Isomers Methylacetylene and Allene