Experimental and theoretical simulations of Titan's VUV photochemistry
type: Dataset
description: Titan's VUV photochemistry is studied by laboratory simulation and numerical modeling.In the laboratory simulations, a gas flow of N2/CH4 (90/10) was irradiated by a continuousVUV (60-350 nm) synchrotron beam in a new reactor, named APSIS (Atmospheric Photochemistry SImulated by Synchrotron). The production of C2-C4 hydrocarbons as well as several nitriles is detected by in situ mass spectrometry and ex situ GC-MS of a cryogenic experiment.Our modeling strategy includes the treatment of uncertain parameters. We propose separaterepresentations of the uncertain photolysis cross-sections and branching ratios. This enables to develop a wavelength-dependent model for the branching ratios.Owing to this separation, in the modeling of Titan's atmosphere, we observe specific altitudes where the uncertainty on the photolysis rate constants vanishes. We show that the Ly-α methane photolysis branching ratios of Wang et al. (2000) and the commonly used 100% CH3 hypothesis for out-of-Ly-α ones should be avoided in Titan's photochemical models. A new ion-neutral coupled model was developed for the APSIS experiments. By this model, ion chemistry and in particular dissociative recombination are found to be very important. We identifed three growth families, of which the most unsaturated one, promoted by C2H2, is dominant. This agrees well with the unsaturated production in Titan's upper atmosphere observed by the Cassini INMS, but not with the in situ MS in the APSIS and Imanaka and Smith (2010)'s experiments, whose saturated productions are substantially higher and likely to originate from the catalysis by metallic walls of the reactors.
identifier: NNT: 2013PA112163
issued: 2026-05-07T23:33:01.085937
language: fr
modified: 2026-05-07T23:33:01.085944
contact point: Organization
  fn: CCSD
keyword: chimothechemical-sciencesother
keyword: incertitude
keyword: infoeu-reposemanticsdoctoralthesis
keyword: laboratory-simulation
keyword: modeling
keyword: modelisation
keyword: photochemistry
keyword: photochimie
keyword: simulation-experimentale
keyword: theses
keyword: titan
keyword: uncertainty
landing page: https://theses.hal.science/tel-00913442

Experimental and theoretical simulations of Titan's VUV photochemistry
type: Distribution
format: HTML
issued: 2026-05-07T23:33:01.102798
modified: 2026-05-07T23:33:01.067843
access URL: https://theses.hal.science/tel-00913442

test_moissonnage_selune
type: Agent