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      Ion chemistry and N-containing molecules in Titan's upper atmosphere

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      Icarus
      Elsevier BV

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          Total Cross Sections for Ionization and Attachment in Gases by Electron Impact. I. Positive Ionization

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            Photochemistry of the atmosphere of Titan: comparison between model and observations.

            The photochemistry of simple molecules containing carbon, hydrogen, nitrogen, and oxygen atoms in the atmosphere of Titan has been investigated using updated chemical schemes and our own estimates of a number of key rate coefficients. Proper exospheric boundary conditions, vertical transport, and condensation processes at the tropopause have been incorporated into the model. It is argued that he composition, climatology, and evolution of Titan's atmosphere are controlled by five major processes: (a) photolysis and photosensitized dissociation of CH4; (b) conversion of H to H2 and escape of hydrogen; (c) synthesis of higher hydrocarbons; (d) coupling between nitrogen and hydrocarbons; (e) coupling between oxygen and hydrocarbons. Starting with N2, CH4, and H2O, and invoking interactions with ultraviolet sunlight, energetic electrons, and cosmic rays, the model satisfactorily accounts for the concentrations of minor species observed by the Voyager IRIS and UVS instruments. Photochemistry is responsible for converting the simpler atmospheric species into more complex organic compounds, which are subsequently condensed at the tropopause and deposited on the surface. Titan might have lost 5.6 x 10(4), 1.8 x 10(3), and 4.0 g cm-2, or the equivalent of 8, 0.25, and 5 x 10(-4) bars of CH4, N2, and CO, respectively, over geologic time. Implications of abiotic organic synthesis on Titan for the origin of life on Earth are briefly discussed.
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              Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update

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                Author and article information

                Journal
                Icarus
                Icarus
                Elsevier BV
                00191035
                November 2007
                November 2007
                : 191
                : 2
                : 722-742
                Article
                10.1016/j.icarus.2007.06.023
                6a09baf6-b6d3-4cd4-8f32-a8d146c71331
                © 2007

                http://www.elsevier.com/tdm/userlicense/1.0/

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