The first measurement of the low-lying states of the neutron-rich ${}^{110}\mathrm{Zr}$ and ${}^{112}\mathrm{Mo}$ was performed via in-beam $\gamma$-ray spectroscopy after one proton removal on hydrogen at $\sim 200\mathrm{MeV}/\text{nucleon}$. The $2_1^{+}$ excitation energies were found at 185(11) keV in ${}^{110}\mathrm{Zr}$, and 235(7) keV in ${}^{112}\mathrm{Mo}$, while the $R_{42}=E(4_1^{+})/E(2_1^{+}$) ratios are 3.1(2), close to the rigid rotor value, and 2.7(1), respectively. These results are compared to modern energy density functional based configuration mixing models using Gogny and Skyrme effective interactions. We conclude that first levels of ${}^{110}\mathrm{Zr}$ exhibit a rotational behavior, in agreement with previous observations of lighter zirconium isotopes as well as with the most advanced Monte Carlo shell model predictions. The data, therefore, do not support a harmonic oscillator shell stabilization scenario at $Z=40$ and $N=70$. The present data also invalidate predictions for a tetrahedral ground state symmetry in ${}^{110}\mathrm{Zr}$.

• Received 16 November 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.032501