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Energy levels and hyperfine structure constants have been compiled for the sixteen longest-lived isotopes of francium (Z=87). Wavelengths with classifications and transition probabilities are also tabulated for 212Fr. In addition, the ionization energy is included for isotopes in which a sufficient number of levels have been measured.
Sansonetti, J.
(2018),
Spectroscopic Data for Neutral Francium (Fr I), J. Phys. & Chem. Ref. Data (JPCRD), National Institute of Standards and Technology, Gaithersburg, MD
(Accessed June 9, 2023)