New ground-state level with spin-parity $1/2^{+}$ is established in ${}^{109}\mathrm{Mo}$, 69.8 keV below the previously reported $5/2^{+}$ ground state in this nucleus, based on precise spectroscopy measurements of $\gamma$ radiation following spontaneous fission of ${}^{248}\mathrm{Cm}$ performed using the Eurogam2 array of anti-Compton spectrometers. Analogous measurement of $\gamma$ radiation following spontaneous fission of ${}^{252}\mathrm{Cf}$, performed using the Gammasphere array, confirms the new $1/2^{+}$ ground state of ${}^{107}\mathrm{Mo}$, proposed recently and establishes the isomeric character of the $5/2^{+}$ first excited state in ${}^{107}\mathrm{Mo}$. Two $\beta$-decaying isomers are suggested in ${}^{111}\mathrm{Mo}$ nucleus based on regular energy systematics, supporting previous predictions. Low-energy excitations in Mo isotopes are interpreted and compared to calculations reported in the literature. The results suggest shape transition from prolate to oblate deformation at $N\ge 67$.

• Received 6 November 2019
• Accepted 29 July 2020

DOI:https://doi.org/10.1103/PhysRevC.102.024318