Effect of resonances on 2s-2p and 2l-3l' excitation of Li-like ions by electron impact

Collision strengths are calculated in a five-state close-coupling approximation for excitation of C3+, O5+, Ne7+, and Ar15+ by electron impact for energies less than the 3d threshold. Resonance contributions enhance the allowed 2p-3s collision strength by larger factors than the enhancement of the forbidden 2s-3s collision strength. The resonance enhancement is approximately independent of nuclear charge Z for 2s-3s, 2s-3p, and 2p-3p, and increases nearly linearly with Z for 2p-3s. The average effect of resonance contributions to Ω(2s,2p) is only 4%