Further evidence on shape coexistence in72As

The ${}^{72}\mathrm{As}$ nucleus was studied via the $(\alpha ,n\gamma )$ reaction at 14.2 MeV bombarding energy. Single $\gamma -,\gamma \gamma$-coincidence, and internal conversion electron spectra were measured with Ge(HP) $\gamma$-ray and superconducting magnetic lens plus Si(Li) electron spectrometers. On the basis of the internal conversion coefficients $\mathrm{of}{}^{72}\mathrm{As}$ transitions, parities of the medium-spin levels up to 1.4 MeV excitation energy were determined, resulting in unambiguous parities also for the heads of the bands observed previously. The states observed were assigned to proton-neutron multiplets on the basis of their decay properties. The energy splittings of the observed multiplets are in accordance with the prediction of the previous interacting boson-fermion-fermion model (IBFFM) calculations using a transitional core lying between the vibrational SU(5) and $\gamma$-soft O(6) limits, except that of the $\pi g_{9/2}\nu g_{9/2}$ multiplet, which was described using the deformed SU(3) core in the present IBFFM calculations. Such a core structure is in accordance with previous particle-rotor and Hartree-Fock-Bogoliubov calculations.