Ionization of Excited Atomic Hydrogen by Electron Collision

A general formula in the Coulomb Born approximation is derived for ionization of the hydrogen atom by electron collision when the atom is in any given initial state. Using this formula, calculations are made for the total ionization cross section and the ionization cross section per unit energy range of the ejected electrons for all substates of the hydrogen atom belonging to the principal quantum numbers $n=1,2,3,4,5\mathrm{}$. In addition, the ionization cross section of one substate from each of the principal quantum numbers $n=6,7,8,9,10\mathrm{}$ are calculated. The tabulated results cover the range of energies of interest in plasma calculations. Although the ionization amplitude is given in parabolic coordinates, the ionization cross section for a particular angular momentum of the atom can be obtained by a transformation of the ionization amplitude to spherical coordinates. Comparisons with experiment and other available theories are given.