Excitation of multiple giant dipole resonances: from spherical to deformed nuclei

12 pages, LateX (elsart); accepted for publication on Phys. Lett. BThe effect of deformation on the excitation of multiple giant dipole resonances is studied. Analytical expressions are derived in the framework of the interacting boson model for the energies and E1 properties of giant dipole resonances in spherical and deformed nuclei, and a numerical treatment of transitional nuclei is proposed. Coulomb-excitation cross sections are calculated in $^{238}$U and in the samarium isotopes