Exotic cluster structure in light neutron-rich nuclei

The cluster structure of C isotopes is investigated using a microscopic alpha+alpha+alpha+n+n... model based on the molecular orbit (MO) model. The stability of the linear chain of 3alpha with respect to the breathing mode and the bending mode for various neutron configurations is investigated. The combination of the valence neutrons in the pi- and sigma-orbits is promising to stabilize for these modes, and the excited states of C-16 with the (3/2(pi)(-))(2)(1/2(sigma)(-))(2) configuration for the four valence neutrons are one of the most promising candidates for such structure. Furthermore, the equilateral-triangular shape of 3a surrounded by valence neutrons is suggested for C-14. The 3(-), 4(-), and 5(-) members of this rotational band appear around the 10Be+alpha threshold, and these calculated states correspond to the experimentally observed 3(-) state (9.80 MeV) and 4(-) state (11.67 MeV). A positive-parity rotational band (0(+), 2(+), 4(+)) also arises around this threshold energy, and these results suggest that the picture of inversion doublet structure works also in neutron-rich nuclei.