Photochemistry of C₃H_p hydrocarbons in Titan’s stratosphere revisited

¹ Université de Bordeaux, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, 33270 Floirac, France
e-mail: hebrard@obs.u-bordeaux1.fr
² CNRS, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, 33270 Floirac, France
³ Université de Bordeaux, Institut des Sciences Moléculaires, UMR 5255, 33400 Talence, France
⁴ CNRS, Institut des Sciences Moléculaires, UMR 5255, 33400 Talence, France

Received: 1 November 2012
Accepted: 22 January 2013

Abstract

The description of C₃ hydrocarbon chemistry in current photochemical models of Titan’s atmosphere is found to be far from complete. We have carefully investigated the photochemistry involving C₃H_p compounds in the atmosphere of Titan (considering both photolysis and neutral reactions), which considerably impacts the abundances of many other hydrocarbon species (including C₂ compounds). Model results indicate that three species (C₃, c-C₃H₂ and C₃H₃) could be abundant enough to be present in the Cassini/INMS data. Because the error bars on predicted C₃-hydrocarbon abundances are considerably larger than those of the observational data, new experimental and theoretical studies targeting the measurement of low-temperature reaction rate constants and product branching ratios are required to reduce current model uncertainties. In particular, we highlight 30 “key reactions”, the uncertainty factors of which should be lowered to improve the quality of photochemical models involving C₃H_p molecules.