Phenomenological description of nuclear rotational spectra by the use of rotational functions in terms of angular momentum

The use of rational fractions in terms of a suitably defined angular momentum variable is further examined for describing the rotational spectra below the Yrast region (I ≲ 30). As a specific example, a four-parameter expression for the moment of inertia is applied and found to fit well the spectra of many good and several soft rotors with spins I ⩽ 22. The systematics of the parameters are also studied. The work is limited to ground-state rotational bands of even-even nuclei.