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Published August 20, 2009 | Published
Journal Article Open

A Crossed Molecular Beams Study on the Formation of the Exotic Cyanoethynyl Radical in Titan's Atmosphere


The reaction of the dicarbon molecule (C2) in its ^(1)Σ_(g) + electronic ground state with hydrogen cyanide HCN(X^(1)Σ^+) is investigated in a crossed molecular beam setup to untangle the formation of the cyanoethynyl radical CCCN(X^(2)Σ^+) in hydrocarbon-rich atmospheres of planets and their moons such as Titan. Combined with electronic structure and rate theory calculations, we show that this elementary reaction is rapid, has no entrance barriers, and yields CCCN via successive rearrangements of the initial HC_(3)N collision complex to the cyanoacetylene intermediate (HCCCN) followed by unimolecular decomposition of the latter without exit barrier. New photochemical models imply that this radical could serve as a key building block to form more complex molecules as observed in situ by the Cassini spacecraft, ultimately leading to organic aerosol particles, which make up the orange-brownish haze layers in Titan's atmosphere.

Additional Information

© 2009 American Astronomical Society. Print publication: Issue 2 (2009 August 20); received 2009 May 4; accepted for publication 2009 June 3; published 2009 August 6. This work was supported by the US National Science Foundation "Collaborative Research in Chemistry Program" (NSF-CRC; CHE-0627854) and by the National Aeronautics and Space Administration (08-PATM08-0053 to SJK and LBH). We thank Chris Parkinson (University of Michigan) and Hiroshi Imanaka (University of Arizona) for valuable discussions and comments on this manuscript. S.J.K. and L.B.H. acknowledge support by the US Department of Energy, Office of the Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under Contract No. DE-AC02-06CH11357. Y.L.Y. was supported by NASA grant NNG06GF33G to the California Institute of Technology; M.C.L. was supported in part by NSC grant 97-2628-M-001- 001 to Academia Sinica.

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