Generalized phenomenological models of the yrast band

The variable moment of inertia model has been generalized so as to be applicable to transitional and vibrational nuclei by requiring that the extended models reduce at low angular momentum, $J$, to the polynomial dependence which agrees with the data. This dictates the introduction of at least three-parameter generalized phenomenological models. Two such models, the generalized variable moment of inertia model and the variable anharmonic vibrator model, are described and then tested against known yrast band data. Except for strongly deformed nuclei, these models substantially improve the agreement with the data.