Among the many fascinating results of the CassiniCHuygens mission, the mass spectrum of the ionosphere of Titan has attracted considerable attention.[1] In brief, the ionosphere was found to be surprisingly complex, consisting of hydrocarbon ions CmHn+ as well as nitrogen-containing ions CnHnNo+ with mass-to-charge ratios up to the probe#s limit of m/z 100;[2] even much heavier components have been proposed.[1b, 3] While the formation of CmHn compounds with m 7 is reasonably well understood,[3C5] routes to larger hydrocarbons are less obvious. Moreover, most of the present models rely on condensation reactions of CmHn+ ions with unsaturated precursors such as acetylene,[6] whereas methane, as the major hydrocarbon in the atmosphere of Titan, only plays a minor role in the subsequent growth processes. Here, we report carboncarbon (C-C) coupling reactions of methane with medium-sized CmHn 2+ dications leading to larger hydrocarbon molecules. Despite lowsteady-state concentrations of the dicationic intermediates, kinetic modeling allows predictions about the larger hydrocarbon species present in the ionosphere of Titan, thereby rationalizing the results from the CassiniCHuygens mission which consideration of monocations only cannot explain.
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