Ca $^+$的4 p $^2$ P $_{1/2,3/2}$精细结构双峰中核处电子密度的意外大差异
Unexpectedly large difference of the electron density at the nucleus in the 4p $^2$P$_{1/2,3/2}$ fine-structure doublet of Ca$^+$
摘要：
我们用光子反冲光谱法测量了单电离钙离子中$^2$ S $_{1/2}$- $^2$ P $_{3/2}$（D2）跃迁的同位素位移。该技术的高精度使我们能够解决这个转变的同位素位移与先前测量的$^2$ S $_{1/2}$ - $^2$ P $_{1/2}$（D1）线的同位素位移之间的差异。提取这种所谓的分裂同位素位移，并显示出明显的场位移贡献特征。从数据中，我们能够提取的场位移系数和质量之间的两个过渡的高精度的小差异。这种J-依赖性是相对论性的起源，并可用于基准原子结构计算。作为第一步，我们使用几种从头计算原子结构的计算方法，提供更准确的值的场位移常数和它们的比例。值得注意的是，从实验数据中提取的场位移常数的比率的高精度值大于所有可用的理论预测。
英文摘要：
We measured the isotope shift in the $^2$S$_{1/2}$-$^2$P$_{3/2}$ (D2) transition in singly-ionized calcium ions using photon recoil spectroscopy. The high accuracy of the technique enables us to resolve the difference between the isotope shifts of this transition to the previously measured isotopic shifts of the $^2$S$_{1/2}$-$^2$P$_{1/2}$ (D1) line. This so-called splitting isotope shift is extracted and exhibits a clear signature of field shift contributions. From the data we were able to extract the small difference of the field shift coefficient and mass shifts between the two transitions with high accuracy. This J-dependence is of relativistic origin and can be used to benchmark atomic structure calculations. As a first step, we use several ab initio atomic structure calculation methods to provide more accurate values for the field shift constants and their ratio. Remarkably, the high-accuracy value for the ratio of the field shift constants extracted from the experimental data is larger than all available theoretical predictions.
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