In-beam [Formula Presented]-ray spectroscopy of [Formula Presented]

Collective structures in ${}^{172}\mathrm{Pt}$ have been investigated by measuring in-beam $\ensuremath{\gamma}$ rays with mass selection and the recoil-decay tagging technique. The discrepancy in the ground-state band from previous studies has been resolved, and a new collective structure that is likely based on an octupole vibration has been identified. A band mixing model is used to determine the properties of the competing near-spherical and deformed ground-state sequences in the light Os-Pt-Hg-Pb region. Evidence for a reduction of deformation in the deformed vacuum structure below $N=98$ is presented.