TEMPERATURE-DEPENDENCE OF HC3N, C6H2, AND C4N2 MID-UV ABSORPTION-COEFFICIENTS - APPLICATION TO THE INTERPRETATION OF TITANS ATMOSPHERIC SPECTRA

Three organic compounds (HC3N, C6H2, and C4N2) relevant of Titan's atm osphere have been studied within the framework of the SIPAT (Spectrosc opie UV d'Interet Prebiologique dans l'Atmosphere de Titan) program. S ince this facility is still unable to reach the very low temperatures (similar to 170 K) of Titan's high atmosphere, spectra have to be obta ined at several absorption-cell temperatures, and the data extrapolate d towards lower temperatures. Previously published HC3N and C6H2 absor ption coefficient data are reviewed, while new spectroscopic data are presented on C4N2. Integrated intensity calculations over the vibratio nal bands are performed apart from the background continuum. Thus, onl y the band contrast is considered here. While, the temperature depende nce of the hot-band integrated intensity follows a Boltzmann distribut ion, we have enhanced the fit through an empirical parametrisation to account for the observed temperature dependence of the C4N2 and HC3N a bsorption coefficients, and to extrapolate those data to the low tempe rature conditions of Titan's high atmosphere. Finally, we discuss the implications of the results to possible detection by remote sensing ob servations of these minor compounds in Titan's atmosphere.