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Published September 22, 2009 | Published + Supplemental Material
Journal Article Open

Chemical dynamics of triacetylene formation and implications to the synthesis of polyynes in Titan's atmosphere


For the last four decades, the role of polyynes such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH) in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an UV radiation shield in planetary environments; thus, acting as prebiotic ozone, and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes that initiate the formation and control the growth of polyynes have been the least understood to date. Here, we present a combined experimental, theoretical, and modeling study on the synthesis of the polyyne triacetylene (HCCCCCCH) via the bimolecular gas phase reaction of the ethynyl radical (CCH) with diacetylene (HCCCCH). This elementary reaction is rapid, has no entrance barrier, and yields the triacetylene molecule via indirect scattering dynamics through complex formation in a single collision event. Photochemical models of Titan's atmosphere imply that triacetylene may serve as a building block to synthesize even more complex polyynes such as tetraacetylene (HCCCCCCCCH).

Additional Information

©2009 by the National Academy of Sciences. Edited by William Klemperer, Harvard University, Cambridge, MA, and approved August 12, 2009 (received for review January 16, 2009). Published online before print September 14, 2009, doi: 10.1073/pnas.0900525106. We thank Dr. Eric Wilson (Jet Propulsion Laboratory, Pasadena, CA) for valuable discussions. This work was supported by National Science Foundation Chemistry Division Grant NSF-CRC CHE-0627854. M.C.L. was supported in part by National Science Council Grant 97-2628-M-001-001 (to Academia Sinica). Author contributions: R.I.K. and A.M.M. designed research; X.G., Y.S.K., A.M.M., M.C.L., and Y.L.Y. performed research; and R.I.K. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/cgi/content/full/0900525106/DCSupplemental.

Attached Files

Published - Gu2009p6015P_Natl_Acad_Sci_Usa.pdf

Supplemental Material - 0900525106SI.pdf


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