Photoionization of Atoms

Abstract

We show that in the high-energy nonrelativistic limit the leading deviations of the energy dependence of the bound-states photoionization cross sections from the asymptotic laws are described by the same factor (called the Stobbe factor). The Stobbe factor cancels in the cross section ratios, making possible an asymptotic analysis. We demonstrate that the variety of forms of electron–photon interactions is connected with the gauge invariance of quantum electrodynamics . We show that the asymptotics for photoionization of s states can be calculated by employing the plane waves in the velocity form for the electron–photon interaction. In the length form one should include also the lowest nonvanishing term of interaction between the photoelectron and the nucleus. The latter should be included in calculations of the asymptotics for ionization of states with $\ell \ne 0$ in both forms. We analyze the Thomas–Reiche–Kuhn sum rules for the case of a nonlocal field. We carry out asymptotic analysis also for the relativistic case. We present the method of inclusion of screening corrections for the relativistic case near the threshold and far away from it. We demonstrate that inclusion of correlations beyond the independent particle approximation (IPA) in the framework of the perturbative approach developed in Chap. 3 enables us to remove the discrepancy between the experimental data and the results of IPA calculations. We show also how inclusion of IPA breaking effects changes the asymptotic behavior of the photoionization cross sections.