Proton-neutron structure of the effective quadrupole-octupole coupled [Formula Presented] transition operator

Electric dipole transitions between [Formula Presented] octupole-phonon states and one-phonon [Formula Presented] mixed-symmetry states of [Formula Presented] [Formula Presented] and [Formula Presented] are observed and provide the first evidence for F-vector [Formula Presented] transitions in nuclei. For effective boson models of the nuclear valence shell, F spin is the analog of isospin in the shell model. The [Formula Presented] transitions are stronger than those of the [Formula Presented] state. The effective [Formula Presented] operator in the sdf-interacting boson model-2 is concluded to have F-vector character, in analogy with the well-known isovector character of the [Formula Presented] operator in microscopic models.