Neutral production of hydrogen isocyanide HNC and hydrogen cyanide HCN in Titans upper atmosphereReport as inadecuate

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1 SSE 2012 L3AB - Laboratoire d-astrodynamique, d-astrophysique et d-aéronomie de bordeaux, OASU - Observatoire aquitain des sciences de l-univers, LAB - Laboratoire d-Astrophysique de Bordeaux Pessac, Université Sciences et Technologies - Bordeaux 1 2 ISM - Institut des Sciences Moléculaires

Abstract : Aims: Following the first detection of hydrogen isocyanide HNC in Titan-s atmosphere, we have devised a new neutral chemical scheme for hydrogen cyanide HCN and HNC in the upper atmosphere of Titan. Methods: Our updated chemical scheme contains 137 compounds with C, H, O and N elements and 788 reactions including 91 photolysis processes. To improve the chemistry of HNC and HCN, a careful review of the literature has been performed to retrieve critical reaction rates and to evaluate their uncertainty factors. We have also estimated the reaction rates of 48 new reactions using simple capture theory. Results: Our photochemical model gives abundances of HNC and HCN in reasonable agreement with observations. An uncertainty propagation study shows large uncertainties for HNC and relatively moderate uncertainties for HCN. A global sensitivity analysis pinpoints some key reactions to study as a priority to improve the predictivity of the model. Conclusions: In particular, our knowledge of the isomerization of HNC via the reaction H + HNC → HCN + H and the chemistry of H2CN needs to be improved. This study of the neutral chemistry taking place in the upper atmosphere of Titan is a prerequisite for future ionospheric models since ion-neutral reactions may also contribute significantly to HNC and HCN production.

Keywords : planets and satellites: individual: Titan planets and satellites: atmospheres planets and satellites: composition astrochemistry

Author: Eric Hébrard - M. Dobrijevic - Jean-Christophe Loison - A. Bergeat - K. M. Hickson -



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