Microscopic description of Coulomb and nuclear excitation of multiphonon states in heavy ion collisions

We calculate the inelastic scattering cross sections to one- and two-phonon states in heavy ion collisions, Both Coulomb and nuclear excitations are included and their interplay is studied. Starting from a microscopic approach based on RPA, we go beyond it in order to treat anharmonicities and take explicitly into account the mixing of two-phonon states among themselves and with one-phonon states. Nonlinear terms in the exciting field are also introduced. These anharmonicities and nonlinearities are shown to have important effects on the cross sections both in the low energy part of the spectrum and in the energy region of the Double Giant Dipole Resonance. (C) 1998 Elsevier Science B.V.