A Crossed Molecular Beam, Low-temperature Kinetics, and Theoretical Investigation of the Reaction of the Cyano Radical (CN) with 1,3-butadiene (C4H6). A Route to Complex Nitrogen-bearing Molecules in Low-temperature Extraterrestrial Environments - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue The Astrophysical Journal Année : 2011

A Crossed Molecular Beam, Low-temperature Kinetics, and Theoretical Investigation of the Reaction of the Cyano Radical (CN) with 1,3-butadiene (C4H6). A Route to Complex Nitrogen-bearing Molecules in Low-temperature Extraterrestrial Environments

André Canosa
Ian R Sims
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Résumé

We present a joint crossed molecular beam and kinetics investigation combined with electronic structure and statistical calculations on the reaction of the ground-state cyano radical, CN(X 2Σ+), with the 1,3-butadiene molecule, H2CCHCHCH2(X 1 A g), and its partially deuterated counterparts, H2CCDCDCH2(X 1 A g) and D2CCHCHCD2(X 1 A g). The crossed beam studies indicate that the reaction proceeds via a long-lived C5H6N complex, yielding C5H5N isomer(s) plus atomic hydrogen under single collision conditions as the nascent product(s). Experiments with the partially deuterated 1,3-butadienes indicate that the atomic hydrogen loss originates from one of the terminal carbon atoms of 1,3-butadiene. A combination of the experimental data with electronic structure calculations suggests that the thermodynamically less favorable 1-cyano-1,3-butadiene isomer represents the dominant reaction product; possible minor contributions of less than a few percent from the aromatic pyridine molecule might be feasible. Low-temperature kinetics studies demonstrate that the overall reaction is very fast from room temperature down to 23 K with rate coefficients close to the gas kinetic limit. This finding, combined with theoretical calculations, indicates that the reaction proceeds on an entrance barrier-less potential energy surface (PES). This combined experimental and theoretical approach represents an important step toward a systematic understanding of the formation of complex, nitrogen-bearing molecules--here on the C5H6N PES--in low-temperature extraterrestrial environments. These results are compared to the reaction dynamics of D1-ethynyl radicals (C2D; X 2Σ+) with 1,3-butadiene accessing the isoelectronic C6H7 surface as tackled earlier in our laboratories.

Dates et versions

hal-00697098 , version 1 (14-05-2012)

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Sébastien B. Morales, Christopher J. Bennett, Sébastien D. Le Picard, André Canosa, Ian R Sims, et al.. A Crossed Molecular Beam, Low-temperature Kinetics, and Theoretical Investigation of the Reaction of the Cyano Radical (CN) with 1,3-butadiene (C4H6). A Route to Complex Nitrogen-bearing Molecules in Low-temperature Extraterrestrial Environments. The Astrophysical Journal, 2011, 742, pp.26. ⟨10.1088/0004-637X/742/1/26⟩. ⟨hal-00697098⟩
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