  Absorption L-lines of iron ions are observed, in absorption, in spectra of
Seyfert 1 galaxies by the new generation of X-ray satellites: Chandra (NASA)
and XMM-Newton (ESA). Lines associated to Fe23+ to Fe17+ are well resolved.
Whereas, those corresponding to Fe16+ to Fe6+ are unresolved. Forbidden
transitions of the Fe16+ to Fe6+ ions were previously observed, for the same
objects, in the visible and infra-red regions, showing that the plasma had a
low density. To interpret X-ray, visible and infra-red data, astrophysical
models assume an extended absorbing medium of very low density surrounding an
intense X-ray source. We have calculated atomic data (wavelengths, radiative
and autoionization rates) for n=2 to n'=3-4 transitions and used them to
construct refined synthetic spectra of the unresolved part of the L-line
spectra.
