The ionization rate of species M due to impact ionization by energetic electrons can be written in the form
where 
is the electron flux at energy E and 
is the
corresponding cross-section [e.g., Li, 1992].
A number of electron and ion losses exist. These include radiative recombination
, dissociative recombination 
, and attachment 
. Typically these loss rates are
given by the product of the number densities of electrons and the interacting species
with a rate coefficient. For instance, the radiative recombination loss rate can be
written
These rate coefficients can be obtained experimentally.