3αclustering in excited states ofC16

Abstract

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