Spectrum of the negative Be ion

The existence of ${\mathrm{Be}}^{-}$ is established from electron correlation calculations which include one-, two-, three-, and four-orbital excitations. The discrete spectrum of ${\mathrm{Be}}^{-}$ consists of three states: $1s^{2}2s2p^2 {}_{}{}^4{}_{}{}^{}P$, $1s^{2}2p^3 {}_{}{}^4{}_{}{}^{}S_{}^o{}_{}{}^{}$, and $1s2s2p^3 {}_{}{}^6{}_{}{}^{}S_{}^o{}_{}{}^{}$. The ${}_{}{}^4{}_{}{}^{}S_{}^o{}_{}{}^{}-{}_{}{}^4{}_{}{}^{}P$ transition offers the possibility of experimental detection of ${\mathrm{Be}}^{-}$, e.g., by beam-foil methods. The theoretical wavelength and probability for the transition are $\lambda =2671\mathrm{}$ Å and $A=0.67\mathrm{}\times {10}^9$ ${\sec }^{-1\mathrm{}}$, respectively.