Uncertainty analysis of bimolecular reactions in Titan ionosphere chemistry model

Abstract : We report about the first detailed uncertainty analysis concerning the kinetics parameters of the ion–molecule reactions included in a Titan's ionospheric chemistry model. Uncertainty propagation has been performed by Monte Carlo sampling. Different possible descriptions of the uncertainties on the rate constants are discussed and compared on the basis of our state of knowledge about ion–molecule reaction rates laboratory measurements. We propose also a new method for the treatment of branching ratios correlated uncertainties. We show that the uncertainty on branching ratios contribute significantly to the uncertainty on ion densities predicted by the chemistry model. Simulation of a mass spectrum for ionic species in Titan ionosphere at 1200 km of altitude and night-time chemistry has been performed and compared to the INMS mass-spectrum available on the website of the NASA left angle brackethttp://photojournal.jpl.nasa.gov/catalog/PIA07865right-pointing angle bracket], corresponding to Cassini's T5 flyby.