Higher order effects in electromagnetic excitation with fast projectiles

Higher order effects in the electromagnetic excitation with fast nuclei are investigated in a systematic way. Since first order (one photon exchange) processes are dominant, a perturbation approach seems appropriate. After a general framework, which is elaborated especially for second order effects, the excitation of ${}_{}{}^{14}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{32}{}_{}{}^{}\mathrm{Cl}$ is discussed as typical examples for an astrophysical application. We find that the method of Coulomb dissociation is in general not affected by higher order effects. The influence of the electromagnetic excitation mechanism on the apparent line shape of the one- and two-phonon giant dipole resonance is studied.