Excited states in the $T_z=\frac{1}{2}$ nucleus ${}^{85}\mathrm{Mo}$ have been observed for the first time with the reaction ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S},\alpha n\gamma )$ at 105 MeV. $\gamma$-ray transitions in this nucleus have been assigned unambiguously by combining the information from the GASP $\gamma$-ray array, the ISIS silicon ball, and the n-Ring neutron detector. Two band structures have been observed in this nucleus; they continue the smooth evolution of the known bands from the lighter $N=43\mathrm{}$ isotones and have been tentatively assigned spins and parity on this basis. After reaching a maximum of collectivity at ${}^{83}\mathrm{Zr},$ the trend with increasing mass is reversed, showing a smaller collectivity at ${}^{85}\mathrm{Mo}.$ The rotational behavior of the observed bands is discussed on the basis of the projected shell model calculations.

• Received 29 May 2001

DOI:https://doi.org/10.1103/PhysRevC.65.034315