Band structures and alignment properties in ${}^{74}\mathrm{Se}$

High-spin states in the even-even nucleus ${}^{74}\mathrm{Se}$ were investigated via the ${}^{65}\mathrm{Cu}{(}^{12}\mathrm{C},{p2n)}^{74}\mathrm{Se}$ reaction at a beam energy of 50 MeV. On the basis of coincidence data three of the known bands were extended to higher spins and two new bands were found. Experimental crossing frequencies were deduced for various band structures and compared with cranked-shell-model results. Previous assignments of $g_{9/2}$ quasiproton and $g_{9/2}$ quasineutron alignments along the yrast line were confirmed when a near-prolate shape is assumed. Hartree-Fock-Bogoliubov calculations predict a deformed shape for excited states in ${}^{74}\mathrm{Se}$ which shows, however, a considerable softness in triaxiality. For the first time in the mass 70 region, band structures and quasiparticle alignments in ${}^{74}\mathrm{Se}$ were also investigated using the projected shell model. The calculations support the previous conclusions for the positive-parity states and predict that the lowest negative-parity bands are signature partners based on $g_{9/2}$ quasiproton excitations, with a $g_{9/2}$ quasineutron crossing at higher frequencies leading to a four-quasiparticle configuration at high spins.