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arXiv · 1410.5325

Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA

M. A. Cordiner·M. Y. Palmer·C. A. Nixon·P. G. J. Irwin·N. A. Teanby·S. B. Charnley·M. J. Mumma·Z. Kisiel·J. Serigano·Y. -J. Kuan·Y. -L. Chuang·K. -S. Wang
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Abstract

We report the first spectroscopic detection of ethyl cyanide (C$_2$H$_5$CN) 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 C$_2$H$_5$CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C$_2$H$_5$CNH$^+$. Here we report the detection of 27 rotational lines from C$_2$H$_5$CN (in 19 separate emission features detected at $>3σ$ confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC$_3$N, CH$_3$CN and CH$_3$CCH were also obtained. In contrast to HC$_3$N, CH$_3$CN and CH$_3$CCH, which peak in Titan's northern (spring) hemisphere, the emission from C$_2$H$_5$CN 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 C$_2$H$_5$CN. Radiative transfer models show that most of the C$_2$H$_5$CN is concentrated at altitudes 300-600 km, suggesting production predominantly in the mesosphere and above. Vertical column densities are found to be in the range (2-5)$\times10^{14}$ cm$^{-2}$.

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M. A. Cordiner, M. Y. Palmer, C. A. Nixon, P. G. J. Irwin, N. A. Teanby, S. B. Charnley, M. J. Mumma, Z. Kisiel, J. Serigano, Y. -J. Kuan, Y. -L. Chuang, K. -S. Wang. 2015-03-10. Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA. https://doi.org/10.1088/2041-8205%2F800%2F1%2Fl14

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