Isospin structure of one- and two-phonon giant dipole resonance excitations

Isospin is included in the description of the Coulomb excitation of multiple giant isovector dipole resonances. In the excitation of even-even nuclei, a relevant portion of the excitation strength is shown to be associated with 1 1 two-phonon states, which tends to be hindered or completely suppressed in calculations in which the isospin degree of freedom is not considered. We find that the excitation cross section is strongly dependent on the ground state isospin. @S0556-2813~99!08105-4#