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Title: Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere

Abstract

Cassini discovered a plethora of neutral and ionized molecules in Titan’s ionosphere including, surprisingly, anions and negatively charged molecules extending up to 13,800 u q{sup −1}. In this Letter, we forward model the Cassini electron spectrometer response function to this unexpected ionospheric component to achieve an increased mass resolving capability for negatively charged species observed at Titan altitudes of 950–1300 km. We report on detections consistently centered between 25.8 and 26.0 u q{sup −1} and between 49.0–50.1 u q{sup −1} which are identified as belonging to the carbon chain anions, CN{sup −}/C{sub 3}N{sup −} and/or C{sub 2}H{sup −}/C{sub 4}H{sup −}, in agreement with chemical model predictions. At higher ionospheric altitudes, detections at 73–74 u q{sup −1} could be attributed to the further carbon chain anions C{sub 5}N{sup −}/C{sub 6}H{sup −} but at lower altitudes and during further encounters extend over a higher mass/charge range. This, as well as further intermediary anions detected at >100 u, provide the first evidence for efficient anion chemistry in space involving structures other than linear chains. Furthermore, at altitudes below <1100 km, the low-mass anions (<150 u q{sup −1}) were found to deplete at a rate proportional to the growth of the larger molecules, amore » correlation that indicates the anions are tightly coupled to the growth process. This study adds Titan to an increasing list of astrophysical environments where chain anions have been observed and shows that anion chemistry plays a role in the formation of complex organics within a planetary atmosphere as well as in the interstellar medium.« less

Authors:
; ; ; ; ; ; ;  [1];  [2];  [3]; ;  [4];  [5]; ;  [6];  [7]
  1. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT (United Kingdom)
  2. Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble (France)
  3. Laboratory for Atmospheric and Space Physics, University of Colorado, Innovation Drive, Boulder, CO 80303 (United States)
  4. Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden)
  5. Space Science and Engineering Division, Southwest Research Institute (SWRI), 6220 Culebra Road, San Antonio, TX 78238 (United States)
  6. NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)
  7. Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala (Sweden)
Publication Date:
OSTI Identifier:
22654427
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 844; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALTITUDE; ASTROPHYSICS; CARBON; CARBON NITRIDES; CORRELATIONS; DETECTION; ELECTRON SPECTROMETERS; FORECASTING; IONOSPHERE; MASS; MOLECULES; PLANETARY ATMOSPHERES; PLANETS; RESPONSE FUNCTIONS; SATELLITE ATMOSPHERES; SATELLITES; SPACE

Citation Formats

Desai, R. T., Coates, A. J., Wellbrock, A., González-Caniulef, D., Jones, G. H., Lewis, G. R., Taylor, S. A., Kataria, D. O., Vuitton, V., Crary, F. J., Shebanits, O., Wahlund, J.-E., Waite, J. H., Cordiner, M., Sittler, E. C., and Edberg, N. J. T., E-mail: r.t.desai@ucl.ac.uk. Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA7851.
Desai, R. T., Coates, A. J., Wellbrock, A., González-Caniulef, D., Jones, G. H., Lewis, G. R., Taylor, S. A., Kataria, D. O., Vuitton, V., Crary, F. J., Shebanits, O., Wahlund, J.-E., Waite, J. H., Cordiner, M., Sittler, E. C., & Edberg, N. J. T., E-mail: r.t.desai@ucl.ac.uk. Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere. United States. doi:10.3847/2041-8213/AA7851.
Desai, R. T., Coates, A. J., Wellbrock, A., González-Caniulef, D., Jones, G. H., Lewis, G. R., Taylor, S. A., Kataria, D. O., Vuitton, V., Crary, F. J., Shebanits, O., Wahlund, J.-E., Waite, J. H., Cordiner, M., Sittler, E. C., and Edberg, N. J. T., E-mail: r.t.desai@ucl.ac.uk. Tue . "Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere". United States. doi:10.3847/2041-8213/AA7851.
@article{osti_22654427,
title = {Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere},
author = {Desai, R. T. and Coates, A. J. and Wellbrock, A. and González-Caniulef, D. and Jones, G. H. and Lewis, G. R. and Taylor, S. A. and Kataria, D. O. and Vuitton, V. and Crary, F. J. and Shebanits, O. and Wahlund, J.-E. and Waite, J. H. and Cordiner, M. and Sittler, E. C. and Edberg, N. J. T., E-mail: r.t.desai@ucl.ac.uk},
abstractNote = {Cassini discovered a plethora of neutral and ionized molecules in Titan’s ionosphere including, surprisingly, anions and negatively charged molecules extending up to 13,800 u q{sup −1}. In this Letter, we forward model the Cassini electron spectrometer response function to this unexpected ionospheric component to achieve an increased mass resolving capability for negatively charged species observed at Titan altitudes of 950–1300 km. We report on detections consistently centered between 25.8 and 26.0 u q{sup −1} and between 49.0–50.1 u q{sup −1} which are identified as belonging to the carbon chain anions, CN{sup −}/C{sub 3}N{sup −} and/or C{sub 2}H{sup −}/C{sub 4}H{sup −}, in agreement with chemical model predictions. At higher ionospheric altitudes, detections at 73–74 u q{sup −1} could be attributed to the further carbon chain anions C{sub 5}N{sup −}/C{sub 6}H{sup −} but at lower altitudes and during further encounters extend over a higher mass/charge range. This, as well as further intermediary anions detected at >100 u, provide the first evidence for efficient anion chemistry in space involving structures other than linear chains. Furthermore, at altitudes below <1100 km, the low-mass anions (<150 u q{sup −1}) were found to deplete at a rate proportional to the growth of the larger molecules, a correlation that indicates the anions are tightly coupled to the growth process. This study adds Titan to an increasing list of astrophysical environments where chain anions have been observed and shows that anion chemistry plays a role in the formation of complex organics within a planetary atmosphere as well as in the interstellar medium.},
doi = {10.3847/2041-8213/AA7851},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 844,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 2017},
month = {Tue Aug 01 00:00:00 EDT 2017}
}