The 1s-2p excitation of hydrogen atoms

Abstract

The second Born approximation is used to calculate the cross sections for the excitation of the 2p states of atomic hydrogen by proton, electron and positron impact, allowance being made for the effect of virtual transitions involving the 1s, 2s and 2p0, ± 1 intermediate states. In the case of proton impact, provided coupling to the 2s intermediate state is excluded from the second Born approximation calculations, good agreement is obtained at high energies with the cross section given by the exact numerical integration of the coupled differential equations connecting the 1s and 2p states. Satisfactory accord is also obtained with the results of close-coupling calculations in which full allowance is made for the 1s, 2s and 2p0, ± 1 states, but exchange is neglected, for the scattering of slow electrons. On the other hand, it is found that the agreement with the cross section resulting from analogous calculations for positron impact is not good.