The affects on Titan atmospheric modeling by variable molecular reaction rates

Date
2017
Authors
Hamel, Mark D.
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Abstract

The main effort of this thesis is to study the production and loss of molecular ions in the ionosphere of Saturn's largest moon Titan. Titan's atmosphere is subject to complex photochemical processes that can lead to the production of higher order hydrocarbons and nitriles. Ion-molecule chemistry plays an important role in this process but remains poorly understood. In particular, current models that simulate the photochemistry of Titan's atmosphere overpredict the abundance of the ionosphere's main ions suggesting a flaw in the modeling process. The objective of this thesis is to determine which reactions are most important for production and loss of the two primary ions, C2H5+ and HCNH+, and what is the impact of uncertainty in the reaction rates on the production and loss of these ions. In reviewing the literature, there is a contention about what reactions are really necessary to illuminate what is occurring in the atmosphere. Approximately seven hundred reactions are included in the model used in this discussion (INT16). This paper studies what reactions are fundamental to the atmospheric processes in Titan's upper atmosphere, and also to the reactions that occur in the lower bounds of the ionosphere which are used to set a baseline molecular density for all species, and reflects what is expected at those altitudes on Titan. This research was conducted through evaluating reaction rates and cross sections available in the scientific literature and through conducting model simulations of the photochemistry in Titan's atmosphere under a range of conditions constrained by the literature source. The objective of this study is to determine the dependence of ion densities of C2H5+ and HCNH+ on the uncertainty in the reaction rates that involve these two ions in Titan's atmosphere.

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Keywords
Atmosphere, Ions, Titan
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Department
Physics and Astronomy