Heavy-ion excitation of one- and two-phonon giant dipole states as an exit doorway phenomenon

We develop a detailed theory for multiphonon excitation in heavy-ion collisions. This theory fully accounts for the effects of the finite lifetimes of the states involved and allows the treatment of both formation and decay of multiphonon states through explicit consideration of spreading and escape widths. A schematic model is used to study the influence of the widths on the formation cross sections. We find that the finite width of the one-phonon resonance leads to a decrease in the two-phonon state cross section.