Reactions and Kinetics of Unsaturated C<sub>2</sub> Hydrocarbon Radicals

Laufer, Allan H.; Fahr, Askar

doi:10.1021/cr030039x

Cited by 112 publications

(81 citation statements)

References 152 publications

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“…0.45% and 0.47% respectively. As expected, 59 the photodissociation of 3,3,3-trifluoropropyne is more efficient by a factor of 2 (0.83%) compared to acetylene. In addition to the high yield of C 2 H radicals, the photolysis of CF 3 C 2 H leaves behind less reactive CF 3 radicals compared to H-atoms from acetylene.…”

Section: Tunable Vuv Isomer-specific Product Detectionsupporting

confidence: 82%

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

Soorkia

Trevitt

Selby³

et al. 2010

J. Phys. Chem. A

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The rate coefficient for the reaction of the ethynyl radical (C 2 H) with 1-butyne (H-C≡C-CH 2 -CH 3 ) is measured in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by laser photolysis of acetylene (C 2 H 2 ) at 193 nm and detected via chemiluminescence (C 2 H + O 2 → CH (A 2 Δ) + CO 2 ). The rate coefficients are measured over the temperature range of 74-295 K. The C 2 H + 1-butyne reaction exhibits no barrier and occurs with rate constants close to the collision limit. The temperature dependent rate coefficients can be fit within experimental uncertainties by the expression k = (2.4 ± 0.5) × 10 -10 (T/295 K) -(0.04 ± 0.03) cm 3 molecule -1 s -1 . Reaction products are detected at room temperature (295 K) and 533 Pa using a Multiplexed Photoionization Mass Spectrometer (MPIMS) coupled to the tunable VUV synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. Two product channels are identified for this reaction: m/z = 64 (C 5 H 4 ) and m/z = 78 (C 6 H 6 ) corresponding to the CH 3 -and H-loss channels, respectively. Photoionization efficiency (PIE) curves are used to analyze the isomeric composition of both product channels. The C 5 H 4 products are found to be exclusively linear isomers composed of ethynylallene and methyldiacetylene in a 4:1 ratio. In contrast, the C 6 H 6 product channel includes two cyclic isomers, fulvene 18(±5)% and 3,4-dimethylenecyclobut-1-ene 32(±8)%, as well as three linear isomers, 2-ethynyl-1,3-butadiene 8(±5)%, 3,4-hexadiene-1-yne 28(±8)% and 1,3-hexadiyne 14(±5)%. Within experimental uncertainties, we do not see appreciable amounts of benzene and an upper limit of 10 % is estimated. Diacetylene (C 4 H 2 ) formation via the C 2 H 5 -loss channel is also thermodynamically possible but cannot be observed due to experimental limitations. The implications of these results for modeling of planetary atmospheres, especially of Saturn's largest moon Titan, are discussed.

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Section: Tunable Vuv Isomer-specific Product Detectionsupporting

confidence: 82%

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

Soorkia

Trevitt

Selby³

et al. 2010

J. Phys. Chem. A

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“…This reaction has also been added to the network. The reaction between C 6 H and CH 4 is based on one between CCH and CH 4 , which has only been studied at 300 K (Laufer & Fahr 2004), and has a rate somewhat below the standard neutral-radical value, possibly suggesting a small activation energy barrier. We assume here nevertheless that its rate coefficient is independent of temperature.…”

Section: Molecules Detected In Tmc-1mentioning

confidence: 99%

Possible gas-phase syntheses for seven neutral molecules studied recently with the Green Bank Telescope

Quan¹,

Herbst

2007

A&A

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Aims. With the Green Bank telescope (GBT), seven neutral molecules have been newly detected or confirmed towards either the cold interstellar core TMC-1 or the hot core source Sgr B2(N) within the last 1-2 years. Towards TMC-1, the new molecules seen are cyanoallene (CH 2 CCHCN) and methyl triacetylene (CH 3 C 6 H) while methyl cyanoacetylene (CH 3 CCCN) and methyl cyanodiacetylene (CH 3 C 5 N) were confirmed. Towards Sgr B2(N), the three newly detected molecules are cyclopropenone (c-C 3 H 2 O), ketenimine (CH 2 CNH), and acetamide (CH 3 CONH 2 ); these are mainly seen in absorption and are primarily located in an envelope around the hot core. In this work, we report a detailed study of the gas-phase chemistry of all seven molecules. Methods. Starting with our updated gas-phase chemical reaction network osu.01.2007, we added formation and depletion reactions to treat the chemistry of each of the seven molecules. Some of these were already in our network but with incomplete chemistry, while most were not in the network at all prior to this work. We assumed the standard physical conditions for TMC-1 and assumed that these also hold for the envelope around Sgr B2(N). Standard pseudo-time-dependent calculations were run for each source.Results. For TMC-1, we reproduced the observed fractional abundances of three detected molecules at early times of 10 5−6 yr and came close to reproducing a fourth. For the halo surrounding Sgr B2(N), our results are more ambiguous: only for ketenimine were we able to match the observed abundance very well.

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“…From an experimental standpoint, complex vibronic couplings have hampered efforts to find a unique absorption peak to monitor the presence and concentration of the radical in, for example, kinetics experiments. 67 In theoretical studies, the strong vibronic coupling and conical intersection between the X 2 Σ + and A 2 Π states can complicate the computation of spectra or reaction dynamics. In addition, although Hartree-Fock and postHartree-Fock methods correctly predict CCH to be linear, "pure" gradient-corrected functionals like BP86, BLYP and PWP86 predict a bent structure with a C-C-H angle of about ∼ 160 o .…”

Section: Ethynyl Radical (·Cch)mentioning

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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Reactions and Kinetics of Unsaturated C₂ Hydrocarbon Radicals

Cited by 112 publications

References 152 publications

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

Possible gas-phase syntheses for seven neutral molecules studied recently with the Green Bank Telescope

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

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Reactions and Kinetics of Unsaturated C2 Hydrocarbon Radicals

Cited by 112 publications

References 152 publications

Reaction of the C2H Radical with 1-Butyne (C4H6): Low-Temperature Kinetics and Isomer-Specific Product Detection

Reaction of the C2H Radical with 1-Butyne (C4H6): Low-Temperature Kinetics and Isomer-Specific Product Detection

Possible gas-phase syntheses for seven neutral molecules studied recently with the Green Bank Telescope

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

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Reactions and Kinetics of Unsaturated C₂ Hydrocarbon Radicals

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection