Extremely deformed neutron-rich light nuclei and molecular structures

Light N=Z nuclei show pronounced alpha-particle clustering for excited states close to the decay thresholds, this fact is well expressed in the Ikeda Diagram. For neutron-rich nuclei for the low lying states, close to the neutron and proton drip line, states with strong deformation appear based on alpha-particle clustering and a concept based of molecular orbitals can be used for the neutrons. Thus the covalent binding between alpha particles due to valence neutrons produces particular structures in light neutron-rich nuclei which have the form of Dimers and Polymers. An extended Ikeda Diagram for neutron-rich nuclei based on clusters as substructures and valence neutrons is obtained. These states are well reproduced in theoretical approaches based on the Antisymmetrized Molecular Dynamics (AMD), where the strong saturation of nuclear forces in clusters and the weak coupling of the valence nucleons are directly seen. Molecular configurations in the beryllium isotopes (9 Be - 12 Be) will be discussed. Rotational isomeric bands in 11-12 Be well above the particle thresholds are identified up to high excitation energies (15-20 MeV). The well established structure of the dimers will serve as building blocks for more extended objects, the polymers in carbon isotopes and heavier nuclei. (author)