David Osborne - Laboratory chemistry relevant to understanding and modeling the ionosphere of Titan

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  Publication Details (including relevant citation   information):

  Nigel G. Adams, L. Dalila Mathews and David Osborne, Jr

  Faraday Discuss., 2010,   147, 323-335

  DOI:  10.1039/C003233F

  Received 23 Feb 2010, Accepted 12   Apr 2010
  First published on the web 02 Aug 2010


  Laboratory data have a dual and critical role in interpreting   information obtained from the Cassini spacecraft in its passes   through the Titan ionosphere. Firstly, in situ mass   spectra are obtained by Cassini and their conversion into   atmospheric molecular composition requires chemical modeling to   create agreement between the observed mass spectra and those   determined from the models. Secondly, once agreement is obtained,   then the chemical model can be considered to represent the   evolution of the Titan atmosphere. As a contribution to these   endeavors in the past, laboratory measurements have been made in   the Selected Ion Flow Tube (SIFT) of the reactions of a series of   ring molecules with the important ionospheric ion   CH3+. These   reactions showed that a dominant reaction channel is association.   In the present study, this work has been extended to reactions of   another important Titan ion   C3H3+.   These ion–molecule reactions have also been studied at room   temperature using a SIFT. Reactions have been studied in detail   with benzene, toluene and pyridine and show again that   association is very important. The loss of ionization in the   ionosphere is then controlled by electron–ion dissociative   recombination of the association ions and their progeny. The   recombination reactions have been studied as a function of   temperature (300 to 550 K) using a flowing afterglow. These   combined data have been used to develop a subset of the chemistry   and test its viability. They have indicated that association of   the important Titan ions with the abundant nitrogen, followed by   switching of the nitrogen for the ring compounds, can build up   larger species, perhaps resulting in multi-rings. Recombination   of such species can affect the ionization balance and provide   species which can contribute to the parallel neutral chemistry.   Species are suggested that should be looked for in the in   situ mass spectra.

  Address (URL): http://pubs.rsc.org/en/Content/ArticleLanding/2010/FD/c003233f