Journal Article

Electron correlation and relativistic effects in the excited states of radium monofluoride

Athanasakis-Kaklamanakis, M., Franchoo, S., Bai, S. W., Lim, J., Perrett, H. A., Gaul, K., Berbalk, J., McGlone, A., Liu, Y. C., Belošević, I., Berger, R., Ahmad, O., Neyens, G., Bissell, M. L., Imgram, P., Wang, Q., Kujanpää, S., Smets, E., Brinson, A., Chrysalidis, K., Skripnikov, L. V., Garcia Ruiz, R. F., Dorne, A., Isaev, T. A., Koszorús, Á., Warbinek, J., Au, M., Pašteka, L. F., Lalanne, L., Wessolek, J., Heinke, R., Lassègues, P., Bernerd, C., Yang, X. F., Giesen, T. F., Nies, L., Field, R. W., Raggio, A., van den Borne, B., Rothe, S., Geldhof, S., Kyuberis, A. A., Udrescu, S.-M., Borschevsky, A., de Groote, R. P., Flanagan, K. T., Nichols, M., Mei, W. C., Breier, A. A., Wilkins, S. G., Hanstorp, D., Reilly, J. R., Zülch, C., Cocolios, T. E., Lynch, K. M., Fajardo-Zambrano, C. M.

2025

Overview

Highly accurate and precise electronic structure calculations of heavy radioactive atoms and their molecules are important for several research areas, including chemical, nuclear, and particle physics. Ab initio quantum chemistry can elucidate structural details in these systems that emerge from the interplay of relativistic and electron correlation effects, but the large number of electrons complicates the calculations, and the scarcity of experiments prevents insightful theory-experiment comparisons. Here we report the spectroscopy of the 14 lowest excited electronic states in the radioactive molecule radium monofluoride (RaF), which is proposed as a sensitive probe for searches of new physics. The observed excitation energies are compared with state-of-the-art relativistic Fock-space coupled cluster 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 energies is studied and found to be important for all states. Heavy-atom molecules can possess complicated electronic structures due to pronounced electron correlation and relativistic effects. Here, the authors describe electronic states of RaF in detail by combining accurate spectroscopy and theory approaches.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 639/638/440/94 / 639/638/563/606 / 639/766/36/1122 / 639/766/36/1123 / 639/766/387/1126 / Accuracy / Angular momentum / Charged particles / Chemistry / Correlation / Electron states / Electronic structure / Electrons / Excitation / Experiments / Fysik / Humanities and Social Sciences / Isotopes / Lasers / multidisciplinary / Nuclear Theory / Particle physics / Physical Sciences / Physics / Quantum chemistry / Quantum electrodynamics / Radium / Relativistic effects / Science / Science (multidisciplinary) / Spectroscopy / Symmetry