- Methylcyanobutadiyne: Synthesis, x-ray structure and photochemistry; Towards an explanation of its formation in the interstellar medium
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Out of this world: A new convenient synthesis of methylcyanobutadiyne (see figure), an interstellar compound, is described. It was characterized by various techniques including X-ray structure determination. Photolysis experiments were carried out on binary gaseous mixtures of interstellar relevant compounds to understand how methylcyanobutadiyne could be formed in the interstellar medium. Copyright
- Kerisit, Nicolas,Toupet, Loic,Trolez, Yann,Guillemin, Jean-Claude
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- Association reactions at low pressure. IV. The HC3N+/HC3N system
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The reactions between HC3N+ and HC3N, and between HC5N+ and HC3N have been examined at pressures from 1 x 10-7 to 1 x 10-3 Torr by ion cyclotron resonance mass spectrometry.The reaction between HC3N+ and HC3N has both a bimolecular reaction path and a termolecular reaction path.The overall bimolecular reaction rate coefficient was found to be 1.3 * 10-9 cm3 s-1.The primary product, HC5N+, represents 90percent of the product ions, while the minor products HC6N2+ and H2C6N2+ each represent 5percent.The termolecular association rate coefficient was 3.7 * 10-24 cm6 s-1 with He as the third body.From double resonance experiments the mean lifetime of the collision complex was determined to be 180 μs.HC5N+ was found to react with HC3N and form the adduct ion H2C8N2+ through both bimolecular and termolecular channels.The bimolecular rate coefficient was 5.0 * 10-10 cm3 s-1 and the termolecular rate coefficient was observed to be 1.2 * 10-22 cm6 s-1 with HC3N as the third body.With He as the stabilizing molecule, the termolecular rate coefficient was 6.0 * 10-24 cm6 s-1.The mean unimolecular lifetime of the collision complex was estimated to be 15 μs and the mean radiative lifetime for the radiative association channel was found to be 89 μs.HC5N+ was found to be formed with excess internal energy and did not react by bimolecular association until relaxed by several nonreactive collisions with HC3N.
- Sen, Atish D.,Huntress, Wesley T.,Anicich, Vincent G.,McEwan, Murray J.,Denison, Arthur B.
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- Synthesis and characterization of 2,4-pentadiynenitrile - A key compound in space science
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(Chemical Equation Presented) Spaced out: Cyanobutadiyne (3) was synthesized in pure form from 1,3-butadiynyltributylstannane (1) and p-toluene-sulfonyl cyanide (2). Diyne 3 might be formed in the atmosphere of Titan or in the interstellar medium by photolysis of mixtures of acetylene and cyanoacetylene or dicyanoacetylene or of butadiyne and dicyanoacetylene. Only 1,6-addition is observed with nucleophiles.
- Trolez, Yann,Guillemin, Jean-Claude
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p. 7224 - 7226
(2007/10/03)
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- Reaction rates of the CN radical with diacetylene and dicyanoacetylene
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Rates of CN reactions with diacetylene (DA) and dicyanoacetylene (DCA) have been measured at room temperature from the decay of the CN radical at various sample pressures by laser induced fluorescence. The rate constants are (4.2 ± 0.2) × 10-10 and (5.4±0.2) × 10-13 in units of cm3 molec-1 s-1 for DA and DCA, respectively, which follow the general pattern of CN reactions with hydrocarbons and nitriles. In the lower temperature circumstellar envelopes and Titan's atmosphere, the CN reaction with C4H2 may be more important, while the reaction with C4N2 may become less important.
- Seki, Kanekazu,Yagi, Mikio,He, Maoqi,Halpern, Joshua B.,Okabe, Hideo
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p. 657 - 662
(2007/10/03)
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- Photochemistry of cyanoacetylene at 193.3 nm
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Cyanoacetylene (CA) is an important minor constituent in the Titan atmosphere and is present in the interstellar medium. The absorption cross section of CA has been measured in the region from 190 to 255 nm with a resolution of 1 nm. The photochemistry of CA at 193.3 nm has been studied using a quadrupole mass spectrometer and a Fourier transform infrared spectrometer for product analysis. From the photolysis of HC3N-D2 and HC3N-CD4 mixtures and a plateau value of 0.3 for the quantum yield (QY) of DC3N (C3N + D2 → DC3N + D), it is concluded that the main dissociation process is HC3N + hv → H + C3N with a QY of 0.30 ± 0.05 and a minor process is HC3N + hv → C2H + CN with a QY equal to or less than 0.02. The remaining process is the formation of metastable CA (a triplet or carbene). The photolysis of CA induces a noticeable pressure decrease and a concomitant formation of a mist. The QY of CA disappearance is 4.5 ± 0.5, which is much higher than that of diacetylene (QY = 2.0 ± 0.5) and of acetylene (QY = 2.3). The rapid mist formation in CA may explain a haze observed in the Titan atmosphere. A detailed mist formation process is not known. The C3N radical disappears partially by C3N + HC3N → C6N2 + H and 2C3N → C6N2. To explain the formation of minor products, HCN, C2H2, HC5N, and C4N2, two processes involving an unspecified CA metastable state or states may be proposed: HC3N* + HC3N → HC5N + HCN and C4N2 + C2H2.
- Seki, Kanekazu,He, Maoqi,Liu, Renzhang,Okabe, Hideo
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p. 5349 - 5353
(2007/10/03)
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- Isomers and reactivity of C3N+: An experimental study
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The C3N+ ion, generated by electron impact on HC3N and C4N2 and as a product in several ion-molecue reactions, was found to exist in two isomeric forms: CCCN+ and cylic C3N+. These forms were distinguished by their different reactivities with a range of neutral reagents in a selected-ion How tube (SIFT). Isomeric identification was made by reference to existing ab initio calculations. The most reactive isomer, CCCN+, was the major form (≥90%) of the C3N+ ion from all sources of production examined and was found to undergo collision-rate reactions with most of the neutral molecules studied c-C3N+ was much less reactive, which implies an activation barrier in its reactions as it is the higher energy form. Product distributions are reported for the reactions of CCCN+, and rate coefficients for the reactions of both isomers with H2, CH4, NH3, M2O, N2, O2, CO, C2H2, HCN, CO2, and C2N2 at 300 ± 5 K are also given.
- Petrie, Simon,McGrath, Kathryn M.,Freeman, Colin G.,McEwan, Murray J.
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p. 9130 - 9136
(2007/10/02)
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- Ion-molecule reactions with carbon chain molecules: reactions with diacetylene and the diacetylene cation
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Reactions of hydrocarbon and carbon/nitrogen ions with diacetylene and of the diacetylene radical cation with various molecules have been examined with a view to molecular growth by ion-molecule reaction.Measurements were performed with a Selected-Ion Flow Tube (SIFT) apparatus at 296 +/- 2 K of the rate constants and product distributions for the reactions of C+, CH3+, C2H2+, C3H+, CN+, C2N+, and C2N2+ with C4H2 and of C4H2+ with H2, CO, C2H2, C2N2, and C4H2.Condensation and association reactions which build up the carbon content of the ion were observed to compete with charge transfer.For the reactions of CN+ and C2N2+ with C4H2 this growth involved the addition of cyanide to the carbon chain.The kinetics of protonation of diacetylene were also investigated.It was possible to bracket the proton affinity of diacetylene between the known proton affinities of HCN and CH3OH with a value for PA(C4H2) = 177 +/- 5 kcal mol-1, which results in a heat of formation for C4H3+ of 305 +/- 5 kcal mol-1.Numerous secondary association reactions were observed to form adduct ions in helium buffer gas at total pressures of a few tenths of a Torr with rates near the collision rate.This was the case for C6H4+ (C4H2+*C2H2), C7H5+ (C3H3+*C4H2), C8H4+ (C4H2+*C4H2), C8H5+ (C4H3+*C4H2), C9H3+ (C5H+*C4H2), C9H4+(C5H2+*C4H2), C9H5+ (C5H3+*C4H2), C10H4+ (C6H2+*C4H2), C10H5+ (C6H3+*C4H2), C11H7+ (C3H3+*(C4H2)2), C12H6+ (C4H2+*(C4H2)2), C9H3N+ (HC5N+*C4H2), and C10H4N+ (C2N+*(C4H2)2) where the reactants are indicated in parentheses.The observed high rates of association imply the formation of chemical bonds in the adduct ions but the structures of these ions were not resolved experimentally.In most instances there seems little basis for preferring acyclic over cyclic adduct ions.
- Dheandhanoo, Seksan,Forte, Leonard,Fox, Arnold,Bohme, Diethard K.
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p. 641 - 648
(2007/10/02)
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