Coexistence of Covalent Superdeformation and Molecular Resonances in an Unbound Region of ¹²Be

The generalized two-center cluster model, which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, ¹²Be=α+α+4N. We discuss the change of the neutrons’ configuration around two α cores from the covalent structure to the ionic one. We show that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of α+⁸He, ⁶He+⁶He, and ⁵He+⁷He. A new type of superdeformation is possible, and we find here a covalent superdeformation with a hybrid configuration of both the covalent and ionic structures. The excitation of these exotic structures through the two-neutron transfer reaction is also discussed.