Laboratory studies of molecular growth in the titan ionosphere

Roland Thissen, Veronique Vuitton, Panayotis Lavvas, Joel Lemaire, Christophe Dehon, Odile Dutuit, Mark A. Smith, Stefano Turchini, Daniele Catone, Roger Yelle, Pascal Pernot, Arpad Somogyi, Marcello Coreno

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Abstract

Experimental simulations of the initial steps of the ion-molecule reactions occurring in the ionosphere of Titan were performed at the synchrotron source Elettra in Italy. The measurements consisted of irradiating gas mixtures with a monochromatic photon beam, from the methane ionization threshold at 12.6 eV, up to and beyond the molecular nitrogen dissociative ionization threshold at 24.3 eV. Three gas mixtures of increasing complexity were used: N2/CH 4 (0.96/0.04), N2ZCH4/C2H 2 (0.96/0.04/0.001), and N2/CH4/C 2H2/C2H4 (0.96/ 0.04/0.001/0.001). The resulting ions were detected with a high-resolution (1 T) FT-ICR mass spectrometer as a function of time and VUV photon energy. In order to interpret the experimental results, a Titan ionospheric model was adapted to the laboratory conditions. This model had previously allowed the identification of the ions detected in the Titan upper atmosphere by the ion neutral mass spectrometer (INMS) onboard the Cassini spacecraft. Comparison between observed and modeled ion densities validates the kinetic model (reactions, rate constants, product branching ratios) for the primary steps of molecular growth. It also reveals differences that we attribute to an intense surface chemistry. This result implies that heterogeneous chemistry on aerosols might efficiently produce HCN and NH3 in the Titan upper atmosphere.

Original languageEnglish (US)
Pages (from-to)11211-11220
Number of pages10
JournalJournal of Physical Chemistry A
Volume113
Issue number42
DOIs
Publication statusPublished - Oct 22 2009

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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Thissen, R., Vuitton, V., Lavvas, P., Lemaire, J., Dehon, C., Dutuit, O., ... Coreno, M. (2009). Laboratory studies of molecular growth in the titan ionosphere. Journal of Physical Chemistry A, 113(42), 11211-11220. https://doi.org/10.1021/jp9050353