Growth of larger hydrocarbons in the ionosphere of titan.
Growth of larger hydrocarbons in the ionosphere of titan.
复制标题
较大的碳氢化合物在泰坦电离层中生长。
DOI：
10.1002/chem.200800524
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
J. Roithová
中科院分区：
文献类型：
--
作者：
C. L. Ricketts;D. Schröder;C. Alcaraz;J. Roithová
在卡西尼-惠更斯使命的许多迷人的结果中，土卫六电离层的质谱引起了相当大的关注。简而言之，电离层被发现是令人惊讶的复杂，由碳氢化合物离子CmHn +以及含氮离子CnHnNo +组成，其质荷比高达探测器#s的m/z 100极限;甚至更重的成分已经被提出。虽然形成CmHn化合物与m 7是合理的理解，路线更大的烃是不太明显。此外，大多数现有的模型依赖于CmHn +离子与不饱和前体（如乙炔）的缩合反应，而甲烷作为土卫六大气中的主要碳氢化合物，在随后的生长过程中只起次要作用。在这里，我们报告的碳碳（C C）偶合反应甲烷与中等大小的CmHn 2+ dications导致更大的烃分子。尽管低稳态浓度的双阳离子中间体，动力学建模允许预测较大的碳氢化合物物种存在于泰坦的电离层，从而合理化的卡西尼-惠更斯使命的结果，考虑只有一价阳离子不能解释。甲烷的活化提出了特别的挑战，通常涉及高能条件或金属催化。在土卫六的大气条件下（低温和低压），小的碳氢离子确实可以与甲烷反应，但速率常数随着尺寸的减小而减小，到目前为止，反应1涉及最大的CmHn +离子在热条件下与甲烷反应。
Among the many fascinating results of the Cassini–Huygens mission, the mass spectrum of the ionosphere of Titan has attracted considerable attention. 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; even much heavier components have been proposed. While the formation of CmHn compounds with m 7 is reasonably well understood, 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, whereas methane, as the major hydrocarbon in the atmosphere of Titan, only plays a minor role in the subsequent growth processes. Here, we report carbon carbon (C C) coupling reactions of methane with medium-sized CmHn 2+ dications leading to larger hydrocarbon molecules. Despite low steady-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 Cassini–Huygens mission which consideration of monocations only cannot explain. The activation of methane poses a particular challenge and usually involves energetic conditions or metal catalysis. Under the conditions of the Titan atmosphere (low temperatures and pressures), small hydrocarbon ions can indeed react with methane, but the rate constants decrease with size, and so far reaction 1 involves the largest CmHn + ion reacting with methane under thermal conditions.