Precise and accurate nuclear electric quadrupole moment of $^{223}$Ra from molecular spectroscopy

C. M. Fajardo-Zambrano; M. Athanasakis-Kaklamanakis; L. Lalanne; J. R. Reilly; O. Ahmad; M. Au; S. W. Bai; J. Berbalk; C. Bernerd; A. A. Breier; K. Chrysalidis; T. E. Cocolios; R. P. de Groote; K. T. Flanagan; S. Franchoo; R. F. Garcia Ruiz; R. Heinke; P. Imgram; Á. Koszorús; P. Lassègues; J. Lim; Y. C. Liu; K. M. Lynch; A. McGlone; W. C. Mei; G. Neyens; L. Nies; A. Raggio; S. Rothe; B. van den Borne; J. Warbinek; J. Wessolek; X. F. Yang

arXiv · 2611.04696

Precise and accurate nuclear electric quadrupole moment of $^{223}$Ra from molecular spectroscopy

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Abstract

Nuclear electric quadrupole moments of unstable isotopes are commonly extracted from laser spectroscopy of the atomic hyperfine structure, where the accuracy is limited to the several-percent level by the available electric-field-gradient (EFG) calculations. In this study, we determine the spectroscopic quadrupole moment of $^{223}$Ra (half-life $t_{1/2} = 11.4$ d) from hyperfine-resolved collinear resonance ionization spectroscopy of the radioactive molecule $^{223}$Ra$^{19}$F. The $X\,^2Σ^+$ electronic ground state of RaF provides a large axial EFG at the radium nucleus that can be calculated with relativistic coupled-cluster theory to sub-percent accuracy. Together with a three-fold improvement in spectral resolution over previous fast-beam measurements of radioactive molecules, this yields $Q_s = +1.211(7)_\mathrm{stat}(2)_\mathrm{syst}(5)_\mathrm{theo}\,e\mathrm{b}$ for $^{223}$Ra with a total uncertainty of 0.73%, approximately three times better than atomic and ionic determinations. This result demonstrates that molecular spectroscopy can provide access to the electromagnetic structure of unstable nuclei with a precision competitive with, and in favorable cases better than, atomic spectroscopy, and may thus be envisioned for studies beyond the limitations of current radioactive-atom experiments.

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C. M. Fajardo-Zambrano, M. Athanasakis-Kaklamanakis, L. Lalanne, J. R. Reilly, O. Ahmad, M. Au, S. W. Bai, J. Berbalk, C. Bernerd, A. A. Breier, K. Chrysalidis, T. E. Cocolios, R. P. de Groote, K. T. Flanagan, S. Franchoo, R. F. Garcia Ruiz, R. Heinke, P. Imgram, Á. Koszorús, P. Lassègues, J. Lim, Y. C. Liu, K. M. Lynch, A. McGlone, W. C. Mei, G. Neyens, L. Nies, A. Raggio, S. Rothe, B. van den Borne, J. Warbinek, J. Wessolek, X. F. Yang. 2026-11-03. Precise and accurate nuclear electric quadrupole moment of $^{223}$Ra from molecular spectroscopy. https://arxiv.org/abs/2611.04696

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