Electron-impact double ionization of beryllium

Time-dependent close-coupling, R-matrix double pseudo-states and distorted-wave methods are used to calculate the electron-impact double ionization cross section for the 1s22s2 ground state of the Be atom. At 1.5 times the double ionization threshold energy, the first two non-perturbative methods predict a cross section of approximately 1.0 × 10−18 cm2 for the direct double ionization of the 2s2 subshell. At 15.0 times the double ionization threshold energy, the perturbative distorted-wave method predicts a cross section of approximately 2.0 × 10−18 cm2 for the indirect single ionization of the 1s2 subshell followed by autoionization. Thus for the Be atom, the peak of the double ionization cross section is approximately two orders of magnitude smaller than the previously well-determined peak of the single ionization cross section. (Some figures in this article are in colour only in the electronic version)