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Athanasakis-Kaklamanakis M, Wilkins SG, Skripnikov LV, Koszorús Á, Breier AA, Ahmad O, Au M, Bai SW, Belošević I, Berbalk J, Berger R, Bernerd C, Bissell ML, Borschevsky A, Brinson A, Chrysalidis K, Cocolios TE, de Groote RP, Dorne A, Fajardo-Zambrano CM, Field RW, Flanagan KT, Franchoo S, Garcia Ruiz RF, Gaul K, Geldhof S, Giesen TF, Hanstorp D, Heinke R, Imgram P, Isaev TA, Kyuberis AA, Kujanpää S, Lalanne L, Lassègues P, Lim J, Liu YC, Lynch KM, McGlone A, Mei WC, Neyens G, Nichols M, Nies L, Pašteka LF, Perrett HA, Raggio A, Reilly JR, Rothe S, Smets E, Udrescu SM, van den Borne B, Wang Q, Warbinek J, Wessolek J, Yang XF, Zülch C. Electron correlation and relativistic effects in the excited states of radium monofluoride. Nat Commun 2025; 16:2139. [PMID: 40032837 DOI: 10.1038/s41467-025-55977-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2024] [Accepted: 01/02/2025] [Indexed: 03/05/2025] Open
Abstract
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.
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