The low-energy excited states in the neutron-deficient nucleus \(^{91}\) Ru were populated via the \(^{58}\) Ni( \(\,^{36}\) Ar, 2p1n \(\gamma\) ) \(\,^{91}\) Ru reaction at a beam energy of 111 MeV. Charged particles, neutrons, and \(\gamma\) rays were emitted in the reactions and detected using a DIAMANT CsI ball, neutron wall, and EXOGAM Ge clover array, respectively. Angular-correlation and linear polarization measurements were performed to determine the spins and parities of the excited states unambiguously. In addition to the previously reported states, a new low-energy-level structure of \(^{91}\) Ru, including one 7/2 \(^{+}\) and two 11/2 \(^{+}\) states, was established. Similar structures have also been reported in lighter \(N=47\) even-odd isotones down to \(^{85}\) Sr, which were expected to come from the three-neutron–hole \(\nu g_{9/2}^{-3}\) configuration. A semiempirical shell model was used to explain the level systematics of the \(N=47\) even-odd isotones. Calculated results indicated that the 7/2 \(^{+}\) and the 11/2 \(^{+}_{1}\) states are mainly associated with the seniority-three \(\nu (g_{9/2})^{-3}\) excitations, while the 11/2 \(^{+}_{2}\) level is most likely interpreted as a seniority \(\upsilon =1\) configuration of three neutron holes in the \(\nu g_{9/2}\) orbital weakly coupled to a \(2^{+}\) excitation of the \(^{88}\) Sr core. A comparison between the calculation and experiment shows that the two 11/2 \(^{+}\) excited states display an increase in mixing with proton number Z added from \(^{87}\) Zr up to \(^{91}\) Ru.
