Science Case 1: Titan Ion Chemistry

Problem description

1. CASSINI/INMS observations of Titan upper atmosphere indicate the presence of ion and molecules which were not expected:
   • which are the key ion-neutral reactions?
   • what are the roles of transport and dynamic?
   • which is the main driver: photons, electrons...?
2. Coupling of a complex chemistry model with even 1D transport model is difficult: it is essential to identify key reactions to mimic the composition of Titan ionosphere. Studies of sensitivity are the methods to do so. We need to integrate reaction rates... and their measurement uncertainties.

Cassini Data

• CASSINI MAPSExplorer
• Sample Ion Mass Spectrum
• PDS Data for Cassini INMS
• PDS Data for Cassini CAPS

Models and models outputs

• Cassini's Titan Tour (A. Brecht)
  Outputs of Fox-Yelle model along Cassini trajectories.

Energetic fluxes (electrons, photons)

Neutral densities

Physical-chemistry databases

• ION chemistry database
  • Content: Ion-molecule reaction rates and branching ratios
  • Creator(s): V.G. Anicich (JPL, retired)
  • Comments: List of reactions used by R. Yelle and V. Vuitton in their model of Titan ionospheric chemistry
  • References: McEwan &Anicich (2007, Mass Spectrometry Reviews 26, 281-)
  • Medium: ".csv" file

• OSU chemical database
  • Content:
  • Creator(s): Eric Herbst (Columbus University, Ohio, USA), updates by Valentine Wakelam (LAB, Univ. Bordeaux I, France) and Eric Herbst
  • Comments: Uncertainties are being introduced
  • References: Lee, Bettend & Herbst (1996, A&AS 119, 111); Smith, Herbst & Chang (2005, MNRAS 350, 323)
  • Medium: ".csv" file

• UDFA: UMIST Database for Astrochemistry
  • Content:
  • Creator(s): T. Millar (Queen´s University Belfast, UK) since 1995
  • Comments: No uncertainties
  • References: Millar, Farquhar & Willacy (1997, A&AS 121, 139); Le Teuff, Millar & Markwick (2000, A&A 146, 157)
  • Medium: Database interface / ".csv" file

• NIST
• Nagoya
• ISSI expert group project (Resp. V. Wakelam)

Expert Laboratories within EuroPlaNet

• Laboratoire d'Astrophysique de Bordeaux (FRANCE)
• Laboratoire de Chimie Physique, Orsay (FRANCE)
• Laboratoire de Planétologie de Grenoble (FRANCE)
• SPAT @ Imperial College, London (UK)

Data conversions/computation

• Conversion of cross sections to reaction rate constants
• Rate constants estimation by Langevin formula
• ...

Bibliography

• GAPHYOR
  • Content:> Bibliographical database on the Properties of Atoms, Molecules, Gases and Plasmas, including Chemical Reactions
  • Creator(s): LPGP, Univ. Paris-Sud, Orsay, France
  • Comments:
  • References:
  • Medium: Database interface
  • Simplified form:
    Enter formula with all elements counts (ex: C1H4 for CH₄) and charge ("+","-" or nothing)
    Formula: Charge:

• AMBDAS: Atomic and Molecular Bibliographical Database
  • Content:Atomic and Molecular Bibliographical Database
  • Creator(s):nternational Atomic Energy Agency, Nuclear Data Section/Atomic and Molecular Data Unit, Vienna, Austria
  • Comments:
  • References:
  • Medium: Database interface

• B. Mitchell: review of electron recombinations