A&. SplccRco.d.15.N0,10,qp.(10)~10)11,1995 zyxwv 0273-1177(94WO144-8 pril*edi,_$ggyy-g om-ii77rp s9.50+0.00 YP THERMALLY UNSTABLE POLYYNES AND N-ORGAMCS OF PLAN-ETOLOGICAL INTEREST: NEW LABORATORY DATA AND IMPLICATIONS FOR THEIR DETECTION BY IN SZTU AND REMOTE SENSING TECHNIQUES A. Aflalaye,* D. Anclrieux,* Y. BCniIan,* P. Bruston,* P. Co&* D. Coscia,* M. C. Gazeau,* M. Khlifi,* P. Paillous,* R. Sternberg,* E. de Vanssay,* J. C. Guillemin** and F. Raulin* zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK * LISA, URA-CNRS 1404, Universitb Paris 12 & 7,6I Avenue du GtW ral a’e Gaulle, F-94010 Crkeil Cedex, France ** Groupe de Recherches de Phy sicochim’e Structurale, VRA-CNRS 704, Universitk de Rennes, Avenue du GtW ral Leclerc, F-35042 Rennes Cedex, France ABSTRACT In the frame of a laboratory program on organic compounds of planetological interest only stable at low temperatures, we are currently studying the gas chromatographic (GC) and mass spectrometric (MS) behaviour of gaseous polyynes and N-organics, together with their UV and IR spectra. We report here new experimental data on triacetylene (C6H2) expected to be present in Titan’s atmosphere and dicyanoacetylene (C4N2), already detected in this environment. The GC-MS behaviour of these compounds has been studied using fused silica wall coated open capillary column and Ion trap mass spectrometer. Quantitative GC-MS analysis is possible if the chromatographic conditions use room temperature, fast separation (less than about 20 minutes) and low partial pressure of these unstable compounds. The limit of detectability of C4N2 by GC-MS analysis is 500 pg, about 50 times higher than that of C6H2. The UV and IR spectra of these compounds, which were only partially available in the literature, have been studied, including at low temperature. The strength of the main signatures (UV absorption coefficients and IR integrated intensities) have been systematically determined. In particular, we report the first quantitative spectroscopic data for CgH2. Such combined experimental studies avoid the risk of wrong diagnostics due to possible chemical contamination. The application of these techniques for searching for these organics in planetary atmospheres is also discussed. INTRODUCTION Several organics only stable at low temperature have been detected or are expected to be present in planetary environments. This is the case of acetylenic compounds such as polyynes C2nH2 (n=2,3,4, ..), and cyanoacetylenic compounds such as cyanopolyynes HC2nCN (n=l,2, ..) and dicyanoacetylene, C4N2. Indeed, acetylene (ethyne= C2H2), diacetylene (butadiyne = C4H2). cyanoacetylene (propynenitrile = HC3N),and dicyanoacetylene (butynedinitrile = C4N2), have already been detected in Titan’s atmosphere /l/. Other polyynes such as CgH2 and CgH2 and cyanopolyynes such as HC5N are expected to be present from the data of recent experiments simulating Titan’s organic chemistry at low temperature /5/. Now, there is a lack of experimental data on the chemical analysis of such organics only stable at low temperature. It is thus of prime importance to systematically determine the spectral characteristics (frequency and line or band intensities) at least in the IR and UV ranges of these compounds, as well as their gas chromatographic (GC) and mass spectroscopic (MS) behaviour, since these techniques are already used or will be used in space mission of planetary exploration, such as the Cassini-Huygens mission to Saturn and Titan.