Formation and distribution of benzene on Titan

V. Vuitton, Roger Yelle, J. Cui

Research output: Contribution to journalArticle

129 Citations (Scopus)

Abstract

We present a study of the formation and distribution of benzene (C6H6) on Titan. Analysis of the Cassini Mass Spectrometer (INMS) measurements of benzene densities on 12 Titan passes shows that the benzene signal exhibits an unusual time dependence, peaking ∼20 s after closest approach, rather than at closest approach. We show that this behavior can be explained by recombination of phenyl radicals (C6H5) with H atoms on the walls of the instrument and that the measured signal is a combination of (1) C6H6 from the atmosphere and (2) C6H6 formed within the instrument. In parallel, we investigate Titan benzene chemistry with a set of photochemical models. A model for the ionosphere predicts that the globally averaged production rate of benzene by ion-molecule reactions is ∼107 cm-7 s-1, of the same order of magnitude as the production rate by neutral reactions of ∼4 × 106 cm-2 s-1. We show that benzene is quickly photolyzed in the thermosphere, and that C6H5 radicals, the main photodissociation products, are ∼3 times as abundant as benzene. This result is consistent with the phenyl/benzene ratio required to match the INMS observations. Loss of benzene occurs primarily through reaction of phenyl with other radicals, leading to the formation of complex aromatic species. These species, along with benzene, diffuse downward, eventually condensing near the tropopause. We find a total production rate of solid aromatics of∼10-15 g cm-2 s-1, corresponding to an accumulated surface layer of ∼3 m.

Original languageEnglish (US)
Article numberE05007
JournalJournal of Geophysical Research: Space Physics
Volume113
Issue number5
DOIs
StatePublished - May 20 2008

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Titan
Benzene
benzene
distribution
Photodissociation
tropopause
condensing
Ionosphere
thermosphere
Mass spectrometers
photodissociation
mass spectrometers
recombination
ionospheres
time dependence
ionosphere
surface layer
surface layers
spectrometer
Ions

ASJC Scopus subject areas

  • Oceanography
  • Astronomy and Astrophysics
  • Atmospheric Science
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)
  • Geophysics
  • Geochemistry and Petrology

Cite this

Formation and distribution of benzene on Titan. / Vuitton, V.; Yelle, Roger; Cui, J.

In: Journal of Geophysical Research: Space Physics, Vol. 113, No. 5, E05007, 20.05.2008.

Research output: Contribution to journalArticle

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