Ethyl cyanide on titan: Spectroscopic detection and mapping using alma

We report the first spectroscopic detection of ethyl cyanide (C₂H₅CN) in Titan's atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/ submillimeter Array (ALMA). The presence of C₂H₅CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C₂H₅CNH⁺. Here we report the detection of 27 rotational lines from C₂H₅CN (in 19 separate emission features detected at >3s confidence) in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC₃N, CH₃CN, and CH₃CCH were also obtained. In contrast to HC₃N, CH₃CN, and CH₃CCH, which peak in Titan's northern (spring) hemisphere, the emission from C₂H₅CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C₂H₅CN. Radiative transfer models show that C₂H₅CN is most concentrated at altitudes ≳200 km, suggesting production predominantly in the stratosphere and above.