Intrinsic structure of two-phonon states in the interacting boson model
  A general study of excitations up to two-phonon states is carried out using the intrinsic-state formalism of the Interacting Boson Model (IBM). Spectra and transitions for the different dynamical symmetries are analyzed and the correspondence with states in the laboratory frame is established. The influence of multi-phonon states is discussed. The approach is useful in problems where the complexity of the IBM spectrum renders the analysis in the laboratory frame difficult. 
J.E. Garcia-Ramos, C.E. Alonso, J.M. Arias, P. Van Isacker and A.   Vitturi