On the Size of Ions Solvated in Helium Clusters
On the Size of Ions Solvated in Helium Clusters
复制标题
关于溶解在氦簇中的离子的大小
DOI：
10.1002/chem.200802554
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Scheier, Paul
中科院分区：
文献类型：
--
作者：
da Silva, Filipe Ferreira;Waldburger, Philipp;Scheier, Paul
氦纳米液滴分别掺杂SF6、C4F8、CCl4、C6H5Br、CH3I和I-2。当X+/- = F+/-、Cl+/-、Br+/-、I+、I-2（+）或CH3I+时，在与自由电子相互作用后，观察到各种带正电和负电的簇离子X+/- He-n。这些离子的产率随簇大小n的变化而下降，其特征尺寸n(s)的范围从F+的n(s)=10.2 +/- 0.6到Br-的n(s)= 22.2 +/- 0.2。卤化物阴离子的N (s)值比相应阳离子的N (s)值大70%左右。离子产率的变化表明第一溶剂化层闭合。我们提出了一个简单的经典模型，从n(s)估计离子半径。假设第一个溶剂化层中的氦密度等于氦的体积密度，人们发现氦中的卤化物阴离子的半径几乎是碱卤化物晶体中的两倍，这表明由于交换相互作用产生的排斥力而形成了阴离子泡。尽管我们的模型很简单，但从它得到的阴离子半径与从超流体氦中卤化物阴离子的迁移率得到的值以及用量子蒙特卡罗方法计算的X-Hen簇阴离子的值在大约10%的范围内一致。
Helium nanodroplets are doped with SF6, C4F8, CCl4, C6H5Br, CH3I, and I-2. Upon interaction with free electrons a variety of positively and negatively charged cluster ions X+/- He-n are observed where X+/- = F+/-, Cl+/-, Br+/-, I+, I-2(+), or CH3I+. The yield of these ions versus cluster size n drops at characteristic sizes n(s) that range from n(s)=10.2 +/- 0.6 for F+ to n(s) = 22.2 +/- 0.2 for Br-. n(s) values for halide anions are about 70% larger than for the corresponding cations. The steps in the ion yield suggest closure of the first solvation shell. We propose a simple classical model to estimate ionic radii from n(s). Assuming the helium density in the first solvation shell equals the helium bulk density one finds that radii of halide anions in helium are nearly twice as large as in alkali halide crystals, indicating the formation of an anion bubble due to the repulsive forces that derive from the exchange interaction. In spite of the simplicity of our model, anion radii derived from it agree within approximately 10% with values derived from the mobility of halide anions in superfluid bulk helium, and with values computed by quantum Monte Carlo methods for X-Hen cluster anions.