Evidence for octupole collectivity in

Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr, 2p) and 92Mo(83Kr, 3n) reactions. The level scheme has been extended up to an excitation energy of ≈ 5 MeV and tentative spin-parity assignments up to I = 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 negativeparity 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 172Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3− state as a collective octupolevibrational state. a e-mail: ertoprak@kth.se (corresponding author)