Excitation of lithium-like ions by electron impacts

The cross sections corresponding to the transitions Q (2s → n p) and for 2 ⩽ n ⩽ 7 have been computed for Be II, N V, and Ne VIII, using the Coulomb-Born approximation. The cross sections Q (2s → 3p) and Q (2s → 7p) have also been computed for a hydrogenic ion with an infinite nuclear charge. The results obtained are compared with the semi-classical and the g treatments. Simple analytic forms are fitted to the calculated cross sections. The corresponding parameters are then extrapolated along the quantum number n and the charge Z . Tables and graphs are given which enable one to rapidly obtain any cross sections of the type Q (2s → n p) in any ion of the lithium isoelectronic series.