3α clustering in excited states of 16C

The alpha-cluster states of C-16 are investigated by using antisymmetrized molecular dynamics. It is shown that two different types of alpha-cluster states exist: triangular and linear-chain states. The former has an approximate isosceles triangular configuration of a particles surrounded by four valence neutrons occupying the sd shell, while the latter has the linearly aligned a particles with (sd)(2)(pf)(2) neutrons. It is found that the structure of the linear-chain state is qualitatively understood in terms of the 3/2(pi)(-) and 1/ 2(sigma)(-) molecular orbits as predicted by molecular-orbital model, but there exists a non-negligible Be-10 + alpha + 2n correlation. The bandhead energies of the triangular and linear-chain rotational bands are 8.0 and 15.5 MeV, and the latter is close to the He-4 + Be-12 and He-6 + 10Be threshold energies. It is also shown that the linear-chain state becomes the yrast state at J(pi) = 10(+) with E-x = 27.8 MeV owing to its very large moment of inertia comparable with hyperdeformation.