Low temperature rate coefficients for the reactions of CN and C2H radicals with allene (CH2CCH2) and methyl acetylene (CH3CCH)

Carty, David; Page, Valery Le; Sims, Ian; Smith, Ian W. M.

doi:10.1016/s0009-2614(01)00682-0

Cited by 96 publications

(126 citation statements)

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“…Carty et al have reported similar temperature trends in the rate coefficients for the CN + allene and CN + propyne reactions measured over 15-294 K. 18 The reaction of C 2 H + benzene has also been shown to have a similar large rate coefficient that remains essentially unaffected by temperature over the 105-295 K temperature range. 12 These rate coefficients are very close to the corresponding hard-sphere collision limit, implying reaction efficiencies close to unity.…”

Section: Discussionmentioning

confidence: 79%

Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

et al. 2009

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Low-temperature rate coefficients are measured for the CN + benzene and CN + toluene reactions using the pulsed Laval nozzle expansion technique coupled with laser-induced fluorescence detection. The CN + benzene reaction rate coefficient at 105, 165, and 295 K is found to be relatively constant over this temperature range, (3.9-4.9) × 10 -10 cm 3 molecule -1 s -1 . These rapid kinetics, along with the observed negligible temperature dependence, are consistent with a barrierless reaction entrance channel and reaction efficiencies approaching unity. The CN + toluene reaction is measured to have a rate coefficient of 1.3 × 10 -10 cm 3 molecule -1 s -1 at 105 K. At room temperature, nonexponential decay profiles are observed for this reaction that may suggest significant back-dissociation of intermediate complexes. In separate experiments, the products of these reactions are probed at room temperature using synchrotron VUV photoionization mass spectrometry. For CN + benzene, cyanobenzene (C 6 H 5 CN) is the only product recorded with no detectable evidence for a C 6 H 5 + HCN product channel. In the case of CN + toluene, cyanotoluene (NCC 6 H 4 CH 3 ) constitutes the only detected product. It is not possible to differentiate among the ortho, meta, and para isomers of cyanotoluene because of their similar ionization energies and the ∼40 meV photon energy resolution of the experiment. There is no significant detection of benzyl radicals (C 6 H 5 CH 2 ) that would suggest a H-abstraction or a HCN elimination channel is prominent at these conditions. As both reactions are measured to be rapid at 105 K, appearing to have barrierless entrance channels, it follows that they will proceed efficiently at the temperatures of Saturn's moon Titan (∼100 K) and are also likely to proceed at the temperature of interstellar clouds (10-20 K).

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Section: Discussionmentioning

confidence: 79%

Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

et al. 2009

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“…Vinyl cyanide, C 2 H 3 CN, a potential precursor of ethyl cyanide and n-propyl cyanide, is formed predominantly in the gas-phase in both the Basic and Select models. This occurs through the reaction of CN with ethylene (C 2 H 4 ), which has been shown experimentally to be rapid over a range of temperatures (Carty et al 2001). The resultant gas-phase vinyl cyanide then accretes onto the grains until greater temperatures are achieved.…”

Section: Cyanidesmentioning

confidence: 99%

Increased complexity in interstellar chemistry: detection and chemical modeling of ethyl formate andn-propyl cyanide in Sagittarius B2(N)

Беллоче

Garrod

Müller

et al. 2009

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Context. In recent years, organic molecules of increasing complexity have been found toward the prolific Galactic center source Sagittarius B2. Aims. We wish to explore the degree of complexity that the interstellar chemistry can reach in star-forming regions. Methods. We carried out a complete line survey of the hot cores Sgr B2(N) and (M) with the IRAM 30 m telescope in the 3 mm range, plus partial surveys at 2 and 1.3 mm. We analyzed this spectral survey in the local thermodynamical equilibrium approximation. We modeled the emission of all known molecules simultaneously, which allows us to search for less abundant, more complex molecules. We compared the derived column densities with the predictions of a coupled gas-phase and grain-surface chemical code.Results. We report the first detection in space of ethyl formate (C 2 H 5 OCHO) and n-propyl cyanide (C 3 H 7 CN) toward Sgr B2(N). The detection of n-propyl cyanide is based on refined spectroscopic parameters derived from combined analyses of available laboratory spectroscopic data. For each molecule, we identified spectral features at the predicted frequencies having intensities compatible with a unique rotation temperature. For an assumed source size of 3 , our modeling yields a column density of 5.4 × 10 16 cm −2 , a temperature of 100 K, and a linewidth of 7 km s −1 for ethyl formate. n-Propyl cyanide is detected with two velocity components having column densities of 1.5 × 10 16 cm −2 and 6.6 × 10 15 cm −2 , respectively, for a source size of 3 , a temperature of 150 K, and a linewidth of 7 km s −1 . The abundances of ethyl formate and n-propyl cyanide relative to H 2 are estimated to be 3.6 × 10 −9 and 1.0 × 10 −9 , respectively. We derived column density ratios of 0.8/15/1 for the related species t-HCOOH/CH 3 OCHO/C 2 H 5 OCHO and 108/80/1 for CH 3 CN/C 2 H 5 CN/C 3 H 7 CN. Our chemical modeling reproduces these ratios reasonably well. It suggests that the sequential, piecewise construction of ethyl and n-propyl cyanide from their constituent functional groups on the grain surfaces is their most likely formation route. Ethyl formate is primarily formed on the grains by adding CH 3 to functional-group radicals derived from methyl formate, although ethanol may also be a precursor. Conclusions. The detection in Sgr B2(N) of the next stage of complexity in two classes of complex molecule, esters and alkyl cyanides, suggests that greater complexity in other classes of molecule may be present in the interstellar medium.

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“…11,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] In order to analyze and account for the presence of hydrocarbon species, modeling studies are of central importance in understanding the complex nature of Titan's atmosphere.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the pulsed nozzle produces much less gas flow, requiring lower pumping speeds while yielding rate coefficients that are in satisfactory agreement with continuous flow measurements, as demonstrated in a collaborative work between Leone and coworkers and I. W. M. Smith and coworkers. 13,25 Although numerous low temperature kinetic measurements of the C 2 H radical with C 2 (in this paper, C n denotes a hydrocarbon species containing n carbon atoms) and C 3 hydrocarbons 30 have been performed during the last decade as well as product branching studies, 17 there are, to our knowledge, only a few measurements of rate coefficients with molecules having longer carbon chain lengths (C 4 and higher). 38,39 As pointed out by Sims and coworkers, 38 highly unsaturated hydrocarbon species with four and more carbon atoms tend to be very unstable compounds because, for example, diacetylene polymerizes easily at room temperature.…”

Section: Introductionmentioning

confidence: 99%

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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Low temperature rate coefficients for the reactions of CN and C2H radicals with allene (CH2CCH2) and methyl acetylene (CH3CCH)

Cited by 96 publications

References 24 publications

Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

Increased complexity in interstellar chemistry: detection and chemical modeling of ethyl formate andn-propyl cyanide in Sagittarius B2(N)

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

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Low temperature rate coefficients for the reactions of CN and C2H radicals with allene (CH2CCH2) and methyl acetylene (CH3CCH)

Cited by 96 publications

References 24 publications

Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

Increased complexity in interstellar chemistry: detection and chemical modeling of ethyl formate andn-propyl cyanide in Sagittarius B2(N)

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

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