Evidence for octupole collectivity in $$^{172}{mathrm {Pt}}$$172Pt

Excited states in the extremely neutron-deficient nucleus $$^{172}{\mathrm {Pt}}$$ were populated via $$^{96}\mathrm {Ru}(^{78}\mathrm {Kr},2p)$$ and $$^{92}\mathrm {Mo}(^{83}\mathrm {Kr},3n)$$ reactions. The level scheme has been extended up to an excitation energy of $$\approx 5~\hbox {MeV}$$ and tentative spin-parity assignments up to $$I^\pi = 18^+$$. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity $$3^-$$. In addition, we observed an E3 transition from this $$3^-$$ state to the ground state, providing direct evidence for octupole collectivity in $$^{172}{\mathrm {Pt}}$$. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the $$3^-$$ state as a collective octupole-vibrational state.