The structure of ${}^{13}$Be was investigated with antisymmetrized molecular dynamics. The variation after spin and parity projections was performed. An unnatural parity $1/2^{-}$ state was suggested to be lower than the $5/2^{+}$ state indicating that vanishing of the $N=8$ magic number occurs in ${}^{13}$Be. A low-lying $3/2^{+}$ state with a $2\hslash \omega$ configuration was also suggested. Developed cluster structures were found in the intruder states. The lowering mechanism of the intruder states was discussed in terms of molecular orbitals around a $2\alpha$ core.

• Received 8 March 2012

DOI:https://doi.org/10.1103/PhysRevC.85.044320