Anomalous excitation energy of the 21+ level in vibration-like nuclei

It is shown that the excitation energies of the first excited states (21+) in vibration-like nuclei are in a systematical way about 15% lower than the values expected from the global properties of these nuclei. Unexpectedly, this is due to low 21+ level excitations and not to high multiphonon level energies. This effect could only be revealed by considering many yrare multiphonon levels in addition to yrast levels. It affects strongly the identification of such multiphonon states.