The photochemical production of aromatics in the atmosphere of Titan
Résumé
The photochemical processes at work in the atmosphere of Titan are very complex and lead to a great variety of compounds with aerosols as an end-product. One of the most complex molecules detected so far is benzene (C6H6). In the present work, we have updated and improved the chemistry of aromatics in order to better understand the main chemical pathways leading to the production of benzene and determine what other aromatics could be produced efficiently in the atmosphere. This new chemical scheme has been incorporated in our 1D photochemical model corresponding to mean conditions. We confirm the importance of ionic chemistry for benzene production in the upper atmosphere and we have found that excited benzene is an important intermediate in benzene production due to the exothermicity of many production reactions. Among the 24 aromatics included in the model, neutral aromatics like toluene (C6H5CH3) and ethylbenzene (C6H5C2H5) are relatively abundant, suggesting in particular that toluene could be detectable in the infrared, and eventually microwave wavelength ranges. However, we obtained large uncertainties on model results highlighting the need for more experiments and theoretical studies to improve the chemistry of aromatics.
List of reactions (with rate constants) and references used in the present model.
List of photodissociations and references used in the present model.
For each reaction included in the model, the integrated column rate scaled to the surface (in cm-2 s-1) and the mean altitude (in km) of the production are given.
In the three following files, we list the key reactions at 300 km, 500 km and 1000 km of altitude for all species in the present model.