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Fr. Shindo, Y. Benilan (LISA-CNRS, universités Paris VII et XII, France), J.-C. Guillemin (LCOB, ENSCR, France), P. Chaquin (LCT, université Paris VI, France), A. Jolly (LISA-CNRS, universités Paris VII et XII,France), F. Raulin (LISA-CNRS, universités Paris VII et XII, France)
Diacetylene (C4H2) the lightest polyyne, has been detected in Titan. Furthermore, the production of triacetylene (C6H2) has been observed in several experimental simulations of Titan’s atmosphere. And finally, C8H2 is known to be a product of diacetylene photochemistry. Polyynes interest lies in the fact that modeling works predict them as a link between the photodissociation of methane in the high atmosphere and the formation of organic aerosols visible on Titan. Vinylacetylene has been detected in experimental simulations, and appears in photochemical modeling works. Its photochemistry leads to acetylene, diacetylene, and to the formation of soot. However, its thermal decomposition reveals the production of volatile aromatics compounds such as benzene, and of polyynes. Consequently, C4H4 might be an important product of Titan chemistry. To confirm these hypotheses, observations are needed. But the interpretation of those observations will require an experimental background including ultraviolet and infrared spectroscopic characteristics, photochemical and kinetic data for such molecules. Unfortunately, for tetracetylene and vinylacetylene, those data are incomplete or unavailable. Indeed, as instability rises with the length of the molecular chain, experimental constraints make experimental measurements difficult to obtain. We were able to obtained the UV and IR spectra of both C6H2 and C8H2, and the IR spectrum of vinylacetylene. These results give some clues on their possible detection by the Cassini-Huygens mission. Firstly, we deduce an upper limit of tetracetylene and vinylacetylene mole fraction on Titan. Secondly, the IR spectrometer CIRS will not have a sufficient resolution to separate C6H2, C8H2 and higher polyynes from their intense band at 620 cm-1. But, as CIRS covers the domain 10-1500 cm-1, it could be able to detect polyynes bands below 300 cm-1,where they are well separated from one to another.
The author(s) of this abstract have provided an email address for comments about the abstract: shindo@lisa.univ-paris12.fr