Double excitation in Li and Be by electron impact: A distorted-wave approach

The distorted-wave approximation is used to calculate the double-electron-excitation cross section of Li${(}^2$S${\mathrm{-}}^4$P) and Be${(}^1$S${\mathrm{-}}^3$P) by electron impact. The distortion in the incident and exit channels incorporates the distortion effects of the static, polarization, and exchange potentials appropriately. The results are compared with the Born-Oppenheimer approximation.