Non-thermal equilibrium parameters of weakly ionized plasmas

Generalized Boltzmann and Saha formulae for populations of atomic levels and degree of ionization for a two-temperature plasma in non-thermal equilibrium are given. Inelastic atom-atom type collisions are taken into account. Calculations based on these formulae are performed for optically thin or Lyman series optically thick hydrogen plasmas. They are in good agreement with results obtained by solving the non-linear set of balance equations numerically. In some cases atom-atom collisions change the results by a few orders of magnitude. The radiative source function of the strongly non-LTE and optically thin plasma is determined. It coincides with the Planck distribution for a wide frequency band.