Molecular Structures and monopole excitations in light neutron-excess systems

Abstract

The generalized two-center cluster model (GTCM), which can treat covalent, ionic and atomic configurations in general systems with two inert cores plus valence nucleons, is formulated on the basis of the microscopic cluster model. In this model, the covalent configurations constructed by the molecular orbital (MO) method and the atomic (or ionic) configuration obtained by the valence bonding (VB) method can be handled in a consistent manner. GTCM is applied to the light neutron-rich system, 12Be = α + α + 4N. The energy spectra are characterized in terms of the excitation degrees of freedom, such as the the excitation of two a relative motion and the neutrons' single particle excitation. A large enhancement in a monopole transition from a ground MO state to the excited states is found, which seems to be consistent to a recent observation. The systematics of the 0+ states in even Be isotopes over a wide range of the excitation energy is also discussed.