Observations of C 2H 6 and C 2H 2 in the stratosphere of Saturn

We have performed high-resolution spectral observations at mid-infrared wavelengths of C ₂H ₆ (12.16 μm), and C ₂H ₂ (13.45 μm) on Saturn. These emission features probe the stratosphere of the planet and provide information on the hydrocarbon photochemical processes taking place in that region of the atmosphere. The observations were performed using our cryogenic echelle spectrometer Celeste, in conjunction with the McMath-Pierce 1.5-m solar telescope in November and December 1994. We used Voyager IRIS CH ₄ observations (7.67 μm) to derive a temperature profile on the saturnian atmosphere for the P ≤ ∼ 1.6 mbar region of the stratosphere. This profile was then used in conjunction with height-dependent volume mixing ratios of each hydrocarbon to determine global abundances for ethane and acetylene. Our ground-based measurements indicate abundances of 6.7 _-2.3 ^+3.3 × 10 ^-6 for C ₂H ₆ (1.0 mbar pressure level), and 3.4 _-1.1 ^+1.5 × 10 ^-7 for C ₂H ₂ (1.6 mbar pressure level). We also derived new mixing ratios from the Voyager mid-latitude IRIS observations; 8.6 ± 0.9 × 10 ^-6 for C ₂ H ₆ (0.1-3.0 mbar pressure level), and 1.6 ± 0.2 × 10 ^-7 for C ₂H ₂ (2.0 mbar pressure level).