Shi-Wei Bai

Molecules containing short-lived isotopes, namely, radioactive molecules, are among the most promising candidates for probing new physics beyond the standard model, although their production and spectroscopic measurements remain technically challenging. Here, we demonstrate an integrated methodology that combines the formation of molecular ion beams in a radio-frequency quadrupole cooler-buncher with collinear laser spectroscopy. As a proof-of-principle experiment, we successfully produce molecular ions BaF + and YbF + via in-trap ion-molecule reactions and perform high-resolution laser spectroscopy of the target molecule BaF 138 . Vibrational and rotational structures of BaF 138 molecules across different electronic states are obtained using resonance-enhanced multiphoton ionization schemes, confirming the feasibility of the proposed methodology. This work establishes a practical route for future formation and spectroscopic studies of short-lived radioactive molecules, such as those containing Ra 225 , at radioactive ion beam facilities.

Nuclear charge radii of neutron-rich Sc 47 – 49 isotopes were measured using collinear laser spectroscopy at CERN-ISOLDE. The new data reveal that the charge radii of scandium isotopes exhibit a distinct trend between N = 20 and N = 28 , with Sc 41 and Sc 49 isotopes having similar values, mirroring the closeness of the charge radii of Ca 40 and Ca 48 . Theoretical models that successfully interpret the radii of calcium isotopes could not account for the observed behavior in scandium radii, in particular the reduced odd-even staggering. Remarkably, the inclusion of the new Sc 49 radius data has unveiled a similar trend in the charge radii of N = 28 isotones and Z = 20 isotopes when adding the protons atop the Ca 48 core and the neutrons atop the Ca 40 core, respectively. We demonstrate that this trend is consistent with the prediction of the seniority model.