Excitation of lithiumlike ions by electron impact

Abstract

Collision strengths $\Omega$ for electron-impact excitation of Civ and Arxvi are calculated in a five-state close-coupling approximation for energies up to 3 times threshold energy. These results are combined with previous calculations for Nv and Neviii and isoelectronic fits are given for $\Omega (2s, 2p)$ and $\Omega (2s, 3l)$, where $l=0, 1, 2$. In addition, polarization of the resonance $2s$, $2p$ line is calculated for Li-like C, N, Ne, and Ar up to 12 times threshold. A common feature is that the polarization changes from positive to negative at about 9 times threshold energy.