A comprehensive review of the present understanding, both theoretical and experimental, of intrinsic and rotational level structures in medium-heavy deformed odd-odd nuclei is presented. A discussion of the various experimental methods is presented, emphasizing the need for a variety of experimental approaches. The odd-odd nuclei that are immediately amenable to fruitful additional study are pointed out. A discussion of the intrinsic level structures, Gallagher-Moszkowski (GM) splittings, Newby (N) shifts, and role of the residual $p-n$ interaction is presented. Currently available data in the rare-earth region allow the empirical determination of 137 GM splittings and 36 N shifts for 25 odd-odd nuclei in the mass region 152⩽$A$⩽188. A new parametrization of the residual $p-n$ interaction is presented which also takes into account the 27 GM splittings and 12 N shifts from the actinide region. Newly discovered features of rotational bands, such as odd-even staggering, and other high-spin phenomena, such as signature inversion and delay in bandcrossing frequency, are discussed. The role of higher-order Coriolis coupling is pointed out. Systematics of the two-quasiparticle excitations, shape coexistence, isomers, and four-quasiparticle states are presented. Calculated results of the two-quasiparticle intrinsic excitations using two methods, the intrinsic level spacings for odd-A neighboring nuclei and the quasiparticle-plus-phonon coupling model, are compared with experiment.

DOI:https://doi.org/10.1103/RevModPhys.70.843