ABSORPTION-COEFFICIENT OF PROPYNENITRILE IN THE MID-UV RANGE FOR THE STUDY OF TITANS ATMOSPHERE - SOLUTION TO SAMPLE CONTAMINATIONS

UV spectroscopy is a powerful diagnostic tool in the study of organic composition and chemical processes in planetary atmospheres such as th at of Titan. The Spectroscopic UV d'Interet Prebiologique dans l'Atmos phere de Titan (SIPAT) laboratory experiment has been developed in ord er to systematically determine at high resolution the absorption coeff icients of expected molecular absorbers in Titan's atmosphere, with th e goal of interpreting mid-UV albedo spectra. We have studied the mid- UV absorption coefficient of propynenitrile (cyanoacetylene), which is a key compound in prebiotic chemistry. In spite of all the precaution s taken during the synthesis of this compound, the samples studied con tain impurities. Using complementary techniques, we have been able to characterize the impurities (mainly acetone and acetonitrile) in the p ropynenitrile gas sample. Thus, we present new absorption coefficients of propynenitrile determined at 298 K and at 0.02 nm resolution betwe en 185 and 200 nm (the wavelength range where acetone presents strong absorption features). A precise determination of impurity mixing ratio s affecting previously published spectra leads to a reevaluation and t he establishment of associated uncertainty values for HC3N absorption coefficients in the 185- to 230-nm range. Finally, these data have bee n corrected for an erroneous wavelength calibration implying a 3 Angst rom shift.