Collective excitations close to the particle threshold

We report on photon scattering (γ,γ′) experiments to measure the detailed dipole strength distribution between about 3 and 10 MeV in the Z=20 Ca isotopic chain and in N=82 nuclei. A concentration of electric dipole strength carrying a considerable part of the total E1 sum rule strength is observed in all examined nuclei below the particle threshold. The experimental results are compared to theoretical predictions and future approaches to study the excitation mode are discussed.