Spectral analysis for systems of atoms and molecules coupled to the quantized radiation field

We consider systems of static nuclei and electrons - atoms and molecules - coupled to the quantized radiation field. The interactions between electron s and the soft mode-s of the quantized electromagnetic field are described by minimal coupling, p --> p - eA(x), where A(x) is the electromagnetic vec tor potential with an ultraviolet cutoff. If the interactions between the e lectrons and the quantized radiation field are turned off, the atom or mole cule is assumed to have at least one bound state. We prove that, for suffic iently small values of the fine structure constant alpha, the interacting s ystem has a ground state corresponding to the bottom of its energy spectrum . For an atom, we prove that:its excited states above the ground state turn into metastable States whose lifetimes we estimate. Furthermore the energy spectrum is absolutely continuous, except, perhaps. in a small interval ab ove the ground state energy and around the threshold energies of the atom o r molecule.