In-beam $\gamma$-ray spectroscopy of ${}^{188}\mathrm{Pb}$ has been carried out using Gammasphere. Time-correlated $\gamma \text{−}\gamma$ coincidence methods have allowed the identification of new structures above and below the two-particle isomeric states. The detailed decay of the proposed $K^{\pi }=8^{-}$, $1\mu \mathrm{s}$ isomer has been established, together with a rotational band based on the isomer. Both decay and band properties confirm the association with a prolate deformation and the two-quasineutron $9∕2^{+}\left[624\right]\otimes 7∕2^{-}\left[514\right]$ configuration. The band structure identified above the ${11}^{-}$ isomer from the two-proton configuration $9∕2^{-}\left[505\right]\otimes 13∕2^{+}\left[606\right]$ has a moment of inertia similar to those of the bands known in heavier isotopes and to the one-quasiproton components, but the perturbations and in-band properties are not as expected for a simple, symmetric oblate deformation. This structure is fed by a $\left({19}^{-}\right)$ isomer. Possible configurations for this and other multiquasiparticle states are discussed in the context of multi-quasiparticle calculations for coexisting deformations. Low-spin structures populated partly from the decay of the $8^{-}$ isomer have also been identified. Several of these may be associated with proposed excited $0^{+}$ states. Their properties, including yrare-yrast $E0$ decays and gamma-ray branching ratios, are analyzed using band-mixing models. These and other analyses support a shape coexistence scenario, with some qualifications.

• Received 6 February 2004

DOI:https://doi.org/10.1103/PhysRevC.69.054318