X-ray emission from thin plasmas. Collisional ionization for atoms and
  ions of H to Zn
  Every observation of astrophysical objects involving a spectrum requires
atomic data for the interpretation of line fluxes, line ratios and ionization
state of the emitting plasma. One of the processes which determines it is
collisional ionization. In this study an update of the direct ionization (DI)
and excitation-autoionization (EA) processes is discussed for the H to Zn-like
isoelectronic sequences. In the last years new laboratory measurements and
theoretical calculations of ionization cross sections have become available. We
provide an extension and update of previous published reviews in the
literature. We include the most recent experimental measurements and fit the
cross sections of all individual shells of all ions from H to Zn. These data
are described using an extension of Younger's and Mewe's formula, suitable for
integration over a Maxwellian velocity distribution to derive the subshell
ionization rate coefficients. These ionization rate coefficients are
incorporated in the high-resolution plasma code and spectral fitting tool SPEX
V3.0.
