Rapid association reactions at low pressure

Impact on the formation of hydrocarbons on titan

V. Vuitton, Roger Yelle, P. Lavvas, S. J. Klippenstein

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Photochemical models of Titan's atmosphere predict that three-body association reactions are the main production route for several major hydrocarbons. The kinetic rate constants of these reactions strongly depend on density and are therefore only important in Titan's lower atmosphere. However, radiative association reactions do not depend on pressure. The possible existence of large rates at low density suggests that association reactions could significantly affect the chemistry of Titan's upper atmosphere and better constraints for them are required. The kinetic parameters of these reactions are extremely difficult to constrain by experimental measurements as the low pressure of Titan's upper atmosphere cannot be reproduced in the laboratory. However, in the recent years, theoretical calculations of kinetics parameters have become more and more reliable. We therefore calculated several radical-radical and radical-molecule association reaction rates using transition state theory. The calculations indicate that association reactions are fast even at low pressure for adducts having as few as four C atoms. These drastic changes have however only moderate consequences for Titan's composition. Locally, mole fractions can vary by as much as one order of magnitude but the column-integrated production and condensation rates of hydrocarbons change only by a factor of a few. We discuss the impact of these results for the organic chemistry. It would be very interesting to check the impact of these new rate constants on other environments, such as giant and extrasolar planets as well as the interstellar medium.

Original languageEnglish (US)
Article number11
JournalAstrophysical Journal
Volume744
Issue number1
DOIs
StatePublished - Jan 1 2012

Fingerprint

association reactions
Titan
low pressure
hydrocarbons
hydrocarbon
upper atmosphere
kinetics
Titan atmosphere
organic chemistry
lower atmosphere
atmosphere
extrasolar planets
reaction rate
adducts
condensation
planets
reaction kinetics
planet
routes
chemistry

Keywords

  • astrochemistry
  • methods: numerical
  • planets and satellites: individual (Titan)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Rapid association reactions at low pressure : Impact on the formation of hydrocarbons on titan. / Vuitton, V.; Yelle, Roger; Lavvas, P.; Klippenstein, S. J.

In: Astrophysical Journal, Vol. 744, No. 1, 11, 01.01.2012.

Research output: Contribution to journalArticle

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