High-spin states in ${}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ were investigated with the ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$${(}^{29}$Si, 2pn${)}^{81}$Rb reaction using a 95.2 MeV ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ beam. γ-γ coincidences were measured with three detectors at 23° and ±100°. The yrast and near-yrast rotational bands in ${}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ have been extended well above the first band crossings, with spin assignments based on the directional correlations of oriented nuclei. The mean lifetimes of many higher levels were measured using the Doppler shift attenuation method. They imply moderate deformations with average transition moments of 2–2.5 eb, except at the sharp band crossing in the negative parity band, where they dip by a factor of 2. The data have been analyzed in terms of the Woods-Saxon cranking model. The crossing observed in the positive-parity band is attributed to the alignment of a $g_{9/2}$ neutron pair. Two negative-parity bands observed above I=(15/2 are suggested to contain ($g_{9/2}$${)}^2$ neutron and proton pairs, respectively.

• Received 9 November 1988

DOI:https://doi.org/10.1103/PhysRevC.39.1359