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Modeling of the Ion-Radical Nitrogen Chemistry in Titan’s Ionosphere with CO-PRISM: Influence of C₂H₂ and CH₂N₂⁺

Presentation #208.01 in the session Titan I: Atmosphere (Oral Presentation)

Published onOct 23, 2023
Modeling of the Ion-Radical Nitrogen Chemistry in Titan’s Ionosphere with CO-PRISM: Influence of C₂H₂ and CH₂N₂⁺

In Titan’s atmosphere, a complex chemistry induced by photolysis and radiolysis of N2 and CH4, results in the formation of gaseous species (radicals, hydrocarbons, nitriles) and solid particles forming Titan’s haze. The Cassini mission unveiled the presence of large charged species in Titan’s ionosphere, highlighting the important role ions (positive and negative) play in the atmospheric reactivity. In addition, the nitrogen-rich compounds are expected to play a key role in the chain of reactions occurring in Titan’s atmosphere. Many laboratory experiments have been developed to investigate the chemical pathways involved in Titan’s atmospheric organic growth. In parallel, photochemical models have substantially advanced our understanding of Titan’s ionospheric chemistry.

Here, we present an investigation of Titan’s low-temperature (150 K) gas phase N2-CH4-based chemistry using both experimental and numerical work: (1) the COsmic Simulation Chamber (COSmIC) at NASA Ames Research Center allows simulating Titan’s atmospheric chemistry at low temperature using a plasma discharge in the stream of a jet-cooled gas expansion; and (2) a 1D chemical network model called CO-PRISM (COSmIC - Plasma Reactivity and Ionization Simulation Model) using a fluid mechanical framework is employed to simulate the ion-neutral chemical reactivity occurring at low temperature in the COSmIC. We have updated the reaction rates in our numerical model and compared our new synthetic mass spectra to those calculated previously and to experimental mass spectra obtained with COSmIC to see the impact of the updated reaction rates. We have also studied the sensitivity of changing plasma conditions on the resulting ion chemistry and investigated specific nitrogen-rich pathways to determine their influence as gas-phase precursors based on new recently-published reaction pathways not considered before in photochemical models. Finally, we have also calculated the elemental composition of the gas-phase products and compared it with the composition of Titan aerosol analogs produced in COSmIC. These results have been compared to other laboratory and numerical simulations, demonstrating the importance of plasma chemistry experiments and modeling to improve our understanding of cold planetary environments.

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