Recently, the first laser spectroscopy measurement of the radioactive RaF molecule has been reported by Ruiz et al. [Nature 581, 396 (2020)]. This and similar molecules are considered to search for the new physics effects. The radium nucleus is of interest as it is octupole-deformed and has close levels of opposite parity. The preparation of such experiments can be simplified if there are reliable theoretical predictions. It is shown that the accurate prediction of the hyperfine structure of the RaF molecule requires to take into account the finite magnetization distribution inside the radium nucleus. For atoms, this effect is known as the Bohr–Weisskopf (BW) effect. Its magnitude depends on the model of the nuclear magnetization distribution which is usually not well known. We show that it is possible to express the nuclear magnetization distribution contribution to the hyperfine structure constant in terms of one magnetization distribution dependent parameter: BW matrix element for 1s-state of the corresponding hydrogen-like ion. This parameter can be extracted from the accurate experimental and theoretical electronic structure data for an ion, atom, or molecule without the explicit treatment of any nuclear magnetization distribution model. This approach can be applied to predict the hyperfine structure of atoms and molecules and allows one to separate the nuclear and electronic correlation problems. It is employed to calculate the finite nuclear magnetization distribution contribution to the hyperfine structure of the ²²⁵Ra⁺ cation and ²²⁵RaF molecule. For the ground state of the ²²⁵RaF molecule, this contribution achieves 4%.

中文翻译：

---

分子中的核磁化分布效应：Ra +和RaF超精细结构。

最近，Ruiz等人报道了放射性RaF分子的首次激光光谱测量。[自然581，396（2020）]。该分子和类似分子被认为是寻找新的物理效应。镭核很有趣，因为它是八极形变的，并且具有相反水平的相对水平。如果有可靠的理论预测，可以简化此类实验的准备工作。结果表明，要精确预测RaF分子的超精细结构，必须考虑到镭核内部的有限磁化分布。对于原子，此效应称为玻尔－魏斯科普夫（BW）效应。其大小取决于通常未知的核磁化分布模型。我们表明，可以根据一个取决于磁化分布的参数来表达核磁化分布对超细结构常数的贡献：相应的类氢离子的s状态。可以从离子，原子或分子的准确实验和理论电子结构数据中提取该参数，而无需明确处理任何核磁化分布模型。这种方法可用于预测原子和分子的超精细结构，并使人们能够分离核和电子相关问题。它用于计算对²²⁵ Ra ⁺阳离子和²²⁵ RaF分子的超精细结构的有限核磁化分布贡献。对于²²⁵ RaF分子的基态，该贡献达到4％。