Cluster correlations for low-lying intruder states of l2Be.

The formation of intruder states in the low-lying states of 12Be = &agr; + &agr; + 4N is studied by applying the generalized two-center cluster model, which can optimize the excess neutrons' orbits depending on the &agr;-&agr; distance. The correlation energy for the intruder states is analyzed from the viewpoint of two different pictures based on the cluster structure: the covalent picture around two a clusters and the binary He-cluster picture. In the covalent picture, the binding energy of (&pgr;-3/2)2(σ+1/2)2, corresponding to ν(0p)4(Is0d)2 in a naive shell model, gains largely owing to the spin-triplet pairing of the 0d-wave neutrons, which is induced by the two-body spin-orbit interaction. The spin-triplet pairing gives rise to the reduction of the kinetic energy and the increase of the attractive spin-orbit interaction for the excess neutrons. As a result of these correlation energies, the v(0p)4(I0d)2 configuration becomes dominant in the ground state. In the binary cluster picture, the correlation energy is investigated from the coupled channels among &agr; + 8He, 6He + 6He, and 5He + 7He. The coupling to 5He + 7He, which is neglected in usual binary-cluster models, plays an important role for a large reduction of kinetic energy and the formation of a pair of the low-lying 0+ states with a close energy spacing recently observed in experiment. The rotational bands are also discussed from the viewpoint of these two cluster pictures. [ABSTRACT FROM AUTHOR]