  A model for the evaluation of charge-state distributions of fast heavy ions
in solid targets is being developed since late eighties in terms of ETACHA
code. Time to time it is being updated to deal with more number of electrons
and non-perturbative processes. The calculation approach of the recent one,
which is formulated for handling the non-perturbative processes better, is
different from the earlier ones. However, the experimental results for the
projectiles up to 28 electrons can be compared with the predictions from any
versions of ETACHA code. Though earlier versions are not meant for the
non-perturbative cases, but the detail comparison suggests that predictions
from an earlier version is somewhat superior to that of the recent version.
However, certain difference up to 4 units of charge found between the earlier
version and experimental results on the mean charge states and charge state
distributions is attributed to nonradiative electron capture taking place at
the exit surface in the influence of wake and dynamic screening effects. This
can be a possible mechanism of multiply charge formation in the electrospray
ionization of big molecules.
