mental program to study the IR spectra of gas phase organics of interest to Titan. After a preliminary work covering In the frame of a program of systematic studies to determine the case of nitriles (Cerceau et al. 1985), we have estabor reassess the absolute intensities of gas phase organics of interest to Titan, we have experimentally studied the IR spectra lished an experimental procedure allowing the systematic in the gas phase of diazomethane, methyl azide, and methyl determination of absolute intensities-with the associated isocyanide, at room temperature, in the 250-4300 cm ؊1 region. uncertainties-of the main IR bands of gas phase com-The absolute intensities, S , of the most intense vibrational pounds in the range 4000-250 cm Ϫ1 (Raulin et al. 1990, bands of these compounds were determined experimentally Khlifi et al. 1990, Khlifi and Raulin 1991, Delpech et al. together with the associated uncertainties. In order to estimate 1994, Nishio et al. 1995, Khlifi et al. 1995), including some the detectability of the selected compounds by infrared spectrosstudies in the far IR range (Khlifi and Raulin 1991) and copy in Titan's atmosphere, our data were compared with Voysome at low temperature (Khlifi et al. 1992a, 1992b). ager IRIS spectra of Titan. Upper limits of, respectively, 5, 5.4, In addition, we are also developing simulation experiand 1.3 ppb on the mean stratospheric abundances are inferred. ments in the laboratory to more specifically study the for-These values are consistent with photochemical modeling of mation of organics in Titan's atmosphere which are only Titan's atmosphere. They appear auspicious for possible detecstable at low temperature (de Vanssay et al. 1995, Coll tion in Titan using upcoming space missions.