The lithium-like 2s 2S-2p 2P transition in solar flares

Accurate wavelengths of the Fe XXIV lithium-like doublet at 192 and 255 A are derived from measurements made in a sample of four solar flares observed with a spectroheliograph aboard Skylab and selected to minimize systematic effects. The mean value of the Fe XXIV doublet interval is determined, and new members of the lithium isoelectronic sequence are identified, including Cr XXII, Mn XXIII, and Ni XXVI. Doublet splitting along the lithium sequence is analyzed in terms of the experimental screening factor, it is found that the doublet separations increase smoothly with charge number along the sequence, and the doublet interval in Ni XXVI is accurately extrapolated. The experimental screening factors are compared with the values predicted by Snyder's (1971) relativistic screening theory, and excellent agreement is found.