Energy dependence of the ionization of highly excited atoms by collisions with excited atoms

Abstract
Approximate analytical expressions are derived for the ionization cross sections in the high- and low-collision-energy limits, using the improved impulse approximation based on the assumption that the electron-atom inelastic-scattering amplitude is a function only of the momentum transfer. Both cases of simultaneous excitation and de-excitation of one of the atoms are discussed. The formulas are applied to the collisions between two excited hydrogen atoms and are found very useful for estimating the cross sections in the wide range of collisions energies.