Electron impact excitation of atomic hydrogen

Abstract

Electron impact cross sections for all inelastic transitions between states of atomic hydrogen, with principal quantum number n=1, 2 or 3, are compared in a number of non-exchange models. These are: (a) close coupling, (b) close coupling with the pseudostate basis of Morgan (1982) and (c) the unitarised Born approximation. Care is taken to establish accurate convergence in L. Results are presented at energies of 35, 41.65, 50 and 54.4 eV with respect to the ground state. It is found that the simple close-coupling approximation, tends to be in poor accord with the pseudostate calculation. However, it is found that there is reasonable agreement between the latter and the Born II approximation. It is concluded that the unitarised Born approximation is a rapid and satisfactory estimator of the cross section at least when exchange is unimportant. Attention is drawn to the sensitivity of the 1s-2s cross section to the choice of pseudostate basis.