Are There Signatures of Harmonic Oscillator Shells Far from Stability? First Spectroscopy of ^{110}Zr.

The first measurement of the low-lying states of the neutron-rich Zr-110 and Mo-112 was performed via in-beam gamma-ray spectroscopy after one proton removal on hydrogen at similar to 200 MeV/nucleon. The 2(1)(+) excitation energies were found at 185(11) keV in Zr-110, and 235(7) keV in Mo-112, while the R-42 = E(4(1)(+))/(E2(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 Zr-110 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 Zr-110.