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[论文解读] Pinning down electron correlations in RaF via spectroscopy of excited states and high-accuracy relativistic quantum chemistry

M. Athanasakis-Kaklamanakis, S. G. Wilkins|arXiv (Cornell University)|Aug 28, 2023
Advanced Chemical Physics Studies被引用 4
一句话总结

本研究结合了放射性分子RaF中11个激发电子态的高分辨率激光光谱与最先进的相对论性福克空间耦合簇（FS-RCC）计算，实验与理论在约8 meV以内实现了99.71%的一致性。该工作确立了高阶电子相关与量子电动力学修正的关键作用，验证了FS-RCC方法在RaF中对对称性破坏矩的高精度研究中的适用性，而RaF是探索标准模型之外物理学的关键体系。

ABSTRACT

We report the spectroscopy of the 14 lowest excited electronic states in the radioactive molecule radium monofluoride (RaF). The observed excitation energies are compared with fully relativistic state-of-the-art Fock-space coupled cluster (FS-RCC) calculations, which achieve an agreement of >=99.64% (within ~12 meV) with experiment for all states. Guided by theory, a firm assignment of the angular momentum and term symbol is made for 10 states and a tentative assignment for 4 states. The role of high-order electron correlation and quantum electrodynamics effects in the excitation energy of excited states is studied, found to be important for all states. Establishing the simultaneous accuracy and precision of calculations is an important step for research at the intersection of particle, nuclear, and chemical physics, including searches of physics beyond the Standard Model, for which RaF is a promising probe.

研究动机与目标

  • 利用高分辨率激光光谱精确测量放射性分子RaF中激发电子态的能量。
  • 检验在对称性测试基础研究中感兴趣的体系RaF中相对论性电子相关处理的准确性。
  • 验证在强相对论效应分子体系中高阶电子相关与量子电动力学修正的有效性。
  • 建立可靠的理论框架，以预测分子对标准模型之外物理学的敏感度。
  • 通过确认电子态的归属并预测未观测到的能级，为未来RaF的高精度研究提供支持。

提出的方法

  • 在ISOLDE设施制备的RaF上进行激光光谱测量，测定至11个电子态的跃迁能量。
  • 采用高精度相对论性福克空间耦合簇（FS-RCC）计算，包含27e-T、CBS、Gaugnt及QED修正。
  • 理论计算引入了超越标准CCSD(T)的高阶电子相关效应，实现了对多参考特征的处理。
  • 通过对比实验能量与理论预测，评估一致性并验证量子化学模型。
  • 基于改进的理论一致性与实验数据，重新评估了态的归属。
  • 利用外推的理论模型识别出预测但尚未观测到的态，并在补充材料中展示。
Figure 1: Example spectra. (a) $G$ ${}^{2}\Pi_{1/2}\leftarrow A$ ${}^{2}\Pi_{1/2}$ ( $v^{\prime}=0\leftarrow v^{\prime\prime}=0$ ). (b) $E$ ${}^{2}\Sigma_{1/2}\leftarrow A$ ${}^{2}\Pi_{1/2}$ ( $v^{\prime}=0\leftarrow v^{\prime\prime}=0$ ). The simulated spectra were constructed using the best-fit mo
Figure 1: Example spectra. (a) $G$ ${}^{2}\Pi_{1/2}\leftarrow A$ ${}^{2}\Pi_{1/2}$ ( $v^{\prime}=0\leftarrow v^{\prime\prime}=0$ ). (b) $E$ ${}^{2}\Sigma_{1/2}\leftarrow A$ ${}^{2}\Pi_{1/2}$ ( $v^{\prime}=0\leftarrow v^{\prime\prime}=0$ ). The simulated spectra were constructed using the best-fit mo

实验结果

研究问题

  • RQ1在RaF中，使用相对论性福克空间耦合簇理论，高阶电子相关与QED修正的建模精度如何？
  • RQ2RaF激发态的实验测量在多大程度上验证了理论对项符号与角动量量子数的归属？
  • RQ3FS-RCC方法能否可靠预测具有多参考特征的重元素相对论性分子的分子能级？
  • RQ4在30,000 cm⁻¹以内的RaF激发态中，实验与理论的一致性如何？这对未来新物理搜索有何启示？
  • RQ5理论上预测但尚未在实验中观测到的RaF中还有哪些额外电子态？

主要发现

  • RaF中11个电子态的理论与实验激发能一致性达到99.71%或更高，偏差仅为约8 meV。
  • 在$H$ ${}^{2} m{ extbackslash Sigma}_{1/2}$态中观察到最高的一致性，实验与理论的一致性达到99.99%。
  • 高阶电子相关与量子电动力学修正被证明是实现该精度水平的关键因素。
  • FS-RCC方法成功处理了RaF中的多参考特征，优于单参考CCSD(T)方法。
  • 预测了三个额外的电子态，但尚未在当前实验时间窗口内观测到。
  • 经验证的理论模型为未来将RaF作为标准模型之外物理学探针的高精度研究提供了可靠基础。
Figure 2: Left: Calculated level diagram of RaF up to 30,000 cm -1 . The levels in red and blue have been observed experimentally, while the levels in yellow could not be searched for within the available time. The term symbols have been assigned according to the 69e-extAE4Z + corrections calculatio
Figure 2: Left: Calculated level diagram of RaF up to 30,000 cm -1 . The levels in red and blue have been observed experimentally, while the levels in yellow could not be searched for within the available time. The term symbols have been assigned according to the 69e-extAE4Z + corrections calculatio

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