Excitation and Ionization of Hydrogen Atoms by Electron Impact

Abstract

The classical cross sections of Gryzinski for the excitation and ionization of atomic hydrogen by electron impacts are compared with existing experimental and theoretical cross sections. For excitation from the ground to the first excited states of atomic hydrogen, the classical cross section reproduces the experimental cross section to within a factor of 2 from the excitation threshold to an electron impact energy of about 20 atomic units. For ionization from the ground state of atomic hydrogen, the classical cross section reproduces the experimental cross section to within a factor of 2 from 0.02 atomic units above threshold to about 400 atomic units. A comparison of the classical cross sections with all available Born-approximation cross sections shows that although the classical cross sections are always smaller, they agree quite well with the Born cross sections except at very high energies. However for energies less than 100 atomic units the classical cross sections always agree with the Born cross sections to better than a factor of three. A comparison of experimental "electron-ion" recombination coefficients and theoretical recombination coefficients, obtained by using the classical cross sections, suggests that at low energies, the classical cross sections for transitions between low excited levels cannot be in error by more than a factor of 2.