Abstract
Theoretical studies of atom-atom collision processes which may be relevant to the interpretation of astrophysical phenomena are reviewed. Work on excitation, ionization, and electron capture in atomic hydrogen by fast protons and ${\mathrm{He}}^{+}$ ions is summarized. Processes involving slow collisions that are listed include radiative charge transfer and association, associative detachment, Penning ionization, spin-change, collision-induced deactivation, mutual neutralization, and rotational excitation.
Highlights
Theoretical studies of atom —atom collision processes which may be relevant to the interpretation of astrophysical phenomena are reviewed
Atom —atom collision processes which are relevant to astrophysical problems appear to occur either at thermal energies or at very high energies
Low-energy collisions require special considerations, but, with the exception of rearrangement processes, high-energy collisions can be described by the Born approximation. It follows that proton-impact cross sections for excitation and ionization of the target species are comparable to, but larger than, those for electron impact for equal velocities of the proton and the electron
Summary
At high energies (E measured in keV), Q(1s; 2s) (11.1/E) P1 —(7.8/E) g and j. May (1965a) has obtained a simple formula for excitation into all the substates corresponding to a particular value of e when e is large. Cross sections for excitation into all the discrete levels. Cross sections for transitions in which the target. Atom is excited have been computed by Carew and Milford (1963), who give results for the target atom in. The cross-section maximum increases to lower energy and, as e; increases, proton impact becomes more efficient than electron impact in causing transitions in the thermal energy range
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