Outer-shell photodetachment of the metastable ${\mathrm{Be}}^{-}$ ${1s}^2{2s2p}^2$ ${}^4{P}^e$ state

We report calculated photodetachment cross sections from the metastable ${\mathrm{Be}}^{-}$ ${1s}^2{2s2p}^2$ ${}^4{P}^e$ state in the photon energy range 0–10 eV. Outer-shell photodetachment takes place in this energy range, which includes the double-ionization threshold ${\mathrm{Be}}^{+}{(}^2{S}^e)$ at $\sim 7\mathrm{eV}$ as well as doubly excited thresholds of the residual atom up to the $\mathrm{Be}{(1s}^{2}2p4f)$ threshold at $\sim 10\mathrm{eV}.$ Therefore, triply excited states of ${\mathrm{Be}}^{-}$ are reached within the selected photon energy. We have implemented the complex scaled configuration interaction method along with a model potential for the ${1s}^2$ core to uncover the first series of ${\mathrm{Be}}^{-}$ ${}^4{L}^o$ resonant states. In this work, four ${}^4{P}^o,$ seven ${}^4{D}^o,$ and two ${}^4{S}^o$ resonances are reported and we compare our cross section with other previous theoretical calculations, that reported none or, at most, two resonances.