The gyromagnetic factor of the low-lying $E_x=684.10\left(19\right)\mathrm{keV}$ isomeric state of the nucleus ${}^{99}\mathrm{Mo}$ was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of $J^{\pi }=11/2^{-}$, with a half-life of $T_{1/2}=742\left(13\right)\mathrm{ns}$. The state of interest was populated and spin-aligned via a single-neutron transfer on a highly enriched ${}^{98}\mathrm{Mo}$ target. A magnetic moment ${\mu }_{\mathrm{expt}.}=-0.627\left(20\right){\mu }_{\mathrm{N}}$ was obtained. This result is far from the Schmidt value expected for a pure single-particle $\nu h_{11/2}$ state. A comparison of experimental spectroscopic properties of this nucleus is made with results of multishell Interacting boson-fermion Model (IBFM-1) calculations. In this approach, the $J^{\pi }=11/2^{-}$ isomeric state in ${}^{99}\mathrm{Mo}$ has a pure $\nu h_{11/2}$ configuration. Its magnetic moment, as well as that of other two excited states could be reasonably well reproduced by reducing the free neutron spin $g$ factor with a quenching factor of 0.45. This low value is not appropriate only for this case, similar values for the quenching factor being also required in order to describe magnetic moments in other nuclei from the same mass region.

• Received 1 February 2021
• Revised 21 July 2021
• Accepted 2 August 2021

DOI:https://doi.org/10.1103/PhysRevC.104.024321