Mass spectrometry of $^{75}$Zn ground and isomeric states from in-trap decay of $^{75}$Cu

Abstract

We report on high-precision mass measurements of the ground and first isomeric state of $^{75}$Zn, performed using the time-of-flight ion-cyclotron-resonance technique at the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN. The isomeric state was produced using in-trap decay of $^{75}$Cu. This marks the first direct investigation of the isomeric state of $^{75}$Zn via mass spectrometry. The isomer was observed at an excitation energy of 123.7(20) keV, in 2$\,σ$ agreement with the value previously determined through decay spectroscopy. In addition, our measurements correct a misassignment of the ground-state mass excess based on a previous measurement by Baruah et al., revising the value to -62681.0(21) keV. To further investigate the earlier discrepancy, we explored the spin-parity assignments of the ground and isomeric states in $^{75}$Zn using Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer theoretical calculations, given the absence of definitive experimental data. In light of the laser spectroscopy results from Wraith et al., our results add strong evidence for a spin-1/2 ground state, which would agree with large-scale shell-model predictions as well as explaining disagreements with the Monte Carlo Shell Model.