Laboratory Studies on the Influence of Hydrogen on Titan-like Photochemistry.

Abstract

Laboratory investigations of photochemical reactions in simulated Titan-like atmospheric systems provide insight into the formation of gas and aerosol products and the influence of different environmental parameters on the types of organic molecules generated. Studying the gas-phase products as a function of reaction time provides further insight into the reaction pathways that lead to organic production. The stable isotopes in the reactants and products serve as tracers and help to disentangle these reaction pathways. We report a time study on the chemical composition and relative abundance of the evolved gas-phase products formed by far-ultraviolet reactions between 5% CH₄ and N₂ in a closed system. Two experimental setups are used, where one fully removes hydrogen from the experimental system using a palladium membrane (hydrogen-poor experiments) and the other does not remove hydrogen during the experiment (hydrogen-rich experiments). Carbon isotope values (δ¹³C) of CH₄, C₂H₆, and C₃H₈ are also reported and are used, along with the gas-phase composition and relative abundance measurements, to constrain the chemical reactions occurring during our experiments. The gas-phase products C₂H₆, C₃H₈, n-C₄H₁₀, iso-C₄H₁₀, n-C₅H₁₂, iso-C₅H₁₂, C₂H₂, C₂H₄, HCN, and CH₃CN were detected, with some variations between both sets of experiments. The hydrogen-poor experiments highlight the importance of hydrogen in the formation of HCN, n-C₅H₁₂, iso-C₅H₁₂, and CH₃CN. By monitoring the chemical composition and the carbon isotopic ratios of the gas phase during CH₄/N₂ photochemistry, especially under a hydrogen-poor and hydrogen-rich environment, the photochemical reaction pathways and the influence of hydrogen on these pathways in a Titan-like atmosphere can be better understood.