Variety of clustering in ${}^{18}\mathrm{O}$

We investigate excited states of ${}^{18}\mathrm{O}$ by using the antisymmetrized molecular dynamics. It is found that five different types of cluster states exist which we call ${}^{14}\mathrm{C}+\alpha$, higher-nodal ${}^{14}\mathrm{C}+\alpha$, two molecular states, and $4\alpha$ linear-chain. The calculated $\alpha$-decay widths are compared with the observed data. The higher-nodal ${}^{14}\mathrm{C}+\alpha$ cluster states reasonably agree with resonances reported by the recent experiments. We predict that the $\alpha$-particle emission is dominant for the ${}^{14}\mathrm{C}+\alpha$ cluster states while the molecular states prefer the ${}^6\mathrm{He}$ emission.

Figure 1

Theoretical energy spectra (left) and experimental energy spectra (right) of ${}^{18}\mathrm{O}$. The levels are classified into the ground, positive-parity ${}^{14}\mathrm{C}+\alpha$ cluster, and negative-parity ${}^{14}\mathrm{C}+\alpha$ cluster bands in some previous works.

Figure 2

Energy as function of quadrupole deformation for $J^{\pi }=0^{+}$ in ${}^{18}\mathrm{O}$. Six configurations are listed which correspond to density distributions shown in Fig. 3.

Figure 3

Density distributions of intrinsic positive-parity states in ${}^{18}\mathrm{O}$ obtained by the variational calculation. Contour lines show the proton density distributions and color plots show the single particle orbits occupied by two valence neutrons. See the text for the detail of each panel.

Figure 4

Energy as function of quadrupole deformation for $J^{\pi }=1^{-}$ in ${}^{18}\mathrm{O}$. Five configurations are listed which correspond to density distributions in Fig. 5.

Figure 5

Density distributions of intrinsic negative-parity states in ${}^{18}\mathrm{O}$ obtained by the variational calculation. The lower panels show the most weakly bound neutron, while the upper panel show the other valence neutron. See the text for the detail of each panel.

Figure 6

Positive-parity energy spectrum of ${}^{18}\mathrm{O}$ up to $J^{\pi }=6^{+}$. Lines show the observed data [28, 33, 47] and any other symbols are notated in the same manner as Figs. 2 and 3. The noncluster states are not shown.

Figure 7

Reduced width amplitude as a function of distance $r$ for $0_2^{+}$ (solid blue line), $0_3^{+}$ (dotted green line), and $0_4^{+}$ (dashed red line) states as the ${}^{14}\mathrm{C}+\alpha$ (left) and ${}^{12}\mathrm{C}+{}^6\mathrm{He}$ (right) channels. It is assumed that the spins of ${}^{4,6}\mathrm{He}$ and ${}^{12,14}\mathrm{C}$, and relative angular momentum between them are zero.

Figure 8

Negative-parity energy spectrum of ${}^{18}\mathrm{O}$ up to $J^{\pi }=7^{-}$. Lines show the observed data [33, 34, 47] and any other symbols are notated in the same manner as Figs. 4 and 5. The noncluster states are not shown.

Figure 9

Spectroscopic factors with respect to the $\alpha$- and ${}^6\mathrm{He}$-channels for the $J^{\pi }=0^{+}$ states.