Breakdown of vibrational motion in the isotopes {sup 110-116}Cd

A systematic study is made of the Cd isotopes {sup 110-116}Cd by making use of available experimental data and interacting boson model calculations incorporating both normal vibrational levels and intruder excitations. At the two-phonon level, the calculations appear to reproduce the data reasonably well in {sup 110-114}Cd, whereas they break down completely for the 0{sup +} states in {sup 116}Cd. At the three-phonon level, systematic deviations occur across the Cd isotopic chain, revealing the breakdown of vibrational motion in low-spin states. Combined with the failure to reproduce {sup 116}Cd at the two-phonon level, it is possible that the Cd isotopes may not represent vibrational systems and that the essential physics of their motion has been missing.