Resonant triply excited states in the photodetachment of ${\mathrm{He}}^{-}$ $1s2s2p{}^4{P}^o$

The K-shell photodetachment of the metastable ${1s2s2p}^4{P}^o$ ${\mathrm{He}}^{-}$ state is calculated ab initio with a complex scaled configuration interaction method in the photon energy region between the $\mathrm{He}\hspace{0.5em}2s2p{}^3{P}^o$ threshold and the second double ionization threshold ${\mathrm{He}}^{+}$ $\mathrm{}(n=2\mathrm{}).$ Within this photon energy range triply excited states of ${\mathrm{He}}^{-}$ are reached and they autoionize through electron detachment plus target excitation. The only two related calculations reported so far from J. Xi and C. Froese-Fischer [Phys. Rev. A 59, 307 (1999)] and H.L. Zhou et al. [Phys. Rev. A 64, 012714 (2001)], showed a strong discrepancy. Our calculation supports the latter of these results and also compares rather well with a very recent experiment by N. Berrah et al. [Phys. Rev. Lett. 88, 093001 (2002)]. Contrary to the previous interpretation, we find that the prominent structures appearing in the photodetachment spectrum above 43 eV are true triply excited state resonances.