INCREASING POSITIVE ION NUMBER DENSITIES BELOW THE PEAK OF ION–ELECTRON PAIR PRODUCTION IN TITAN'S IONOSPHERE
INCREASING POSITIVE ION NUMBER DENSITIES BELOW THE PEAK OF ION–ELECTRON PAIR PRODUCTION IN TITAN'S IONOSPHERE
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DOI：
10.1088/0004-637x/786/1/69
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发表时间：
2014-04
期刊：
影响因子：
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通讯作者：
E. Vigren;M. Galand;O. Shebanits;J. Wahlund;W. Geppert;P. Lavvas;V. Vuitton;R. Yelle
中科院分区：
文献类型：
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作者：
E. Vigren;M. Galand;O. Shebanits;J. Wahlund;W. Geppert;P. Lavvas;V. Vuitton;R. Yelle
我们将导出的离子-电子对形成率与卡西尼无线电等离子体波科学朗缪尔探测器对泰坦阳光照射的电离层中电子和正离子数密度的测量结合起来。我们表明，尽管有效离子电子复合系数增加，但土卫六阳光照射的电离层中的正离子数密度可以向比离子电子对形成峰值低得多的高度增加。这是因为负离子的混合比例增加了，负离子是由电子附着在中性粒子上而形成的。虽然这一过程充当自由电子的汇，但由于离子-阴离子中和反应的速率系数小于离子-电子解离复合反应的速率系数，因此正离子的寿命变得更长。
We combine derived ion–electron pair formation rates with Cassini Radio Plasma Wave Science Langmuir Probe measurements of electron and positive ion number densities in Titan's sunlit ionosphere. We show that positive ion number densities in Titan's sunlit ionosphere can increase toward significantly lower altitudes than the peak of ion–electron pair formation despite that the effective ion–electron recombination coefficient increases. This is explained by the increased mixing ratios of negative ions, which are formed by electron attachment to neutrals. While such a process acts as a sink for free electrons, the positive ions become longer-lived as the rate coefficients for ion–anion neutralization reactions are smaller than those for ion–electron dissociative recombination reactions.