On the basis of a limited critical review of present theory and experiment, cross sections are recommended for the ionization of any level of hydrogen or any hydrogenic ion by electrons, for the excitation of any level from the ground level and n→n + 1 excitation from higher levels. Individual angular momentum and Stark states of the levels are not considered. We rely on a few experimental results for excitation and ionization, together with theoretical estimates of relative cross sections to obtained recommended cross sections for a variety of processes, which are inaccessible to direct experiment. The normalized energy of the incoming electron is = E/U where E is the energy of the incoming electron, and U the ionization energy of the atom or ion. A normalized cross section is defined as where Z is the nuclear charge, n the initial principal quantum number and Q the cross section. The recommended normalized cross sections for ionization are The cross section QR,1→n() for excitation of neutral hydrogen from the ground level n = 1 to the n = 2 level is presented graphically. The recommended cross section for excitation to an arbitrary final level is For any excitation of neutral hydrogen from a level n ≠ 1 to a neighbouring level, the cross sections of Saraph are recommended. The recommended cross sections for excitation of the ground levels of ions are more complicated, but are based on the Born cross sections for neutral hydrogen.
State-selective electron capture in ArH collisions for charge-exchange recombination spectroscopy