Excitation and ionization of atomic hydrogen from various states

Abstract

For large energies E1 of the impinging electrons, the cross sections Q for optically allowed excitation and ionization of atoms are given by Q = A/E1 ln cE1, where A and c are constants for one transition. For excitation A is proportional to the optical oscillator strength for the transition. For ionization A is proportional to a quantity M2 which can be derived with one of the sum rules for the oscillator strengths.

For excitation, values of cU (U is excitation energy) are calculated here using known values of Born cross sections for large E1 or using known values of quantities related to cU. It is indicated how excitation cross sections for small E1 can be calculated approximately with known values of A and c. It is pointed out that this method probably will be more reliable than “classical” methods.

For ionization, values of M2> and cU>(U> is ionization energy) are calculated. Large discrepancies between cU> values for the same transitions are found, when calculated from (theoretical) cross sections given by different authors. As a possible explanation of these discrepancies, it is indicated that the contribution of the optically disallowed transitions to the total cross sections can be very important, even for large E1. Further, a comparison with classical collision theories is made.