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Y. Sekine (Univ. of Tokyo/NASA ARC), H. Imanaka, B.N. Khare, E.L.O. Bakes (SETI Inst./NASA ARC), C.P. McKay (NASA ARC), S. Sugita, T. Matsui (Univ. of Tokyo)
One of the key processes to understand the atmospheric chemistry of Titan is the removal of hydrogen (H) atom formed by photochemistry because the low concentration of H atom is necessary for unsaturated hydrocarbons to be stable in the atmosphere [1]. Previous theoretical studies suggest interactions of H atom with another H in the organic haze forming H2 molecule as one of the removal process of H atoms in the stratosphere of Titan [1, 2, 3]. However, there has been no experimental study to investigate interactions of H with Titan haze analogs, termed Titan tholin. In this study, we conduct laboratory experiment to irradiate deuterium (D) atom to Titan tholin formed from N2/CH4 gas mixtures and analyze both the gas products and the change in the infrared spectra of the tholin due to irradiations. Our experimental results indicate that interactions of D (H) atom with Titan tholin are composed of three reactions; a) abstraction of hydrogen forming HD (H2) gas, b) addition of D (H) atom into tholin (hydrogenation of tholin), and c) removal of carbon and/or nitrogen from tholin as methane and/or ammonia. Furthermore, we find that unsaturated bonds in Titan tholin are lost by forming saturated bonds due to D atom irradiation indicating that the addition of D atom (hydrogenation) proceeds more efficiently than the abstraction of H. These results strongly suggest that the organic haze is an efficient sink of H atom in Titan's atmosphere. In particular, an efficient capturing of H atom into the organic haze may reduce the concentrations of both atomic and molecular hydrogen in Titan's stratosphere from the calculation results by photochemical models. [1] Yung et al., 1984, Astrophys. J. Sup., vol.55, 465; [2] Bakes et al., 2003, Icarus, 161, 468; [3] Lebonnois et al., 2003, Icarus, 161, 474
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.