Stratospheric composition of Titan from Cassini/CIRS observations

We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard Cassini mission during the first Titan fly-by (July 2-3 2004). The spectra characterize essentially regions around Titan's south pole and up to 5 deg S (with higher emission angles) from the emission observed in the 3 CIRS detectors (covering roughly the 10-1500 cm^-1 spectral range with a 0.53 cm^-1 apodized resolution). The composite spectrum shows a large variety of molecular signatures : hydrocarbons, nitriles and 3 oxygen components. We have used a temperature profile retrieved by inversion of the emission observed in the methane ν ₄ band at 1304 cm-^-1 and a line-by-line radiative transfer code to infer the abundances of the trace constituents in Titan's stratosphere. We compare these mixing ratios with values retrieved two Titan seasons ago by V1 and V2 IRIS observations and with more recent disk-averaged Infrared Space Observatory (ISO) results.