  A model assuming coherent quadrupole-octupole vibrations and rotations is
applied to describe non-yrast energy sequences with alternating parity in
several even-even nuclei from different regions, namely $^{152,154}$Sm,
$^{154,156,158}$Gd, $^{236}$U and $^{100}$Mo. Within the model scheme the yrast
alternating-parity band is composed by the members of the ground-state band and
the lowest negative-parity levels with odd angular momenta. The non-yrast
alternating-parity sequences unite levels of $\beta$-bands with higher
negative-parity levels. The model description reproduces the structure of the
considered alternating-parity spectra together with the observed B(E1), B(E2)
and B(E3) transition probabilities within and between the different
level-sequences. B(E1) and B(E3) reduced probabilities for transitions
connecting states with opposite parity in the non-yrast alternating-parity
bands are predicted. The implemented study outlines the limits of the
considered band-coupling scheme and provides estimations about the collective
energy potential which governs the quadrupole-octupole properties of the
considered nuclei.

Nuclear Theory;Nuclear Experiment;Quantum Physics