Influence of multipole effects on the cross section and alignment following inner-shell ionization of atoms by a linearly polarized photon

Abstract

On the basis of the fully relativistic Dirac-Fock treatment of single ionization by a linearly polarized photon with regard to the E1, M1, E2, M2, and E3 multipoles of the radiative field as well as their interference, we have assessed the influence of multipole effects on the cross sections and alignment parameters A20 and A22 of the residual ions, taking the 3p3/2 and 3d3/2 vacancies of selected Zn and Zn-like Kr6+, Cd18+, and Xe24+ ions as examples. Starting from the most general method of density matrix theory, we carried out specific analytic expressions in terms of the reduced matrix elements of multipole fields, corresponding to different ion-core states. It is shown that the multipole contributions to the photoionization cross sections can be considerable, the character of which becomes more evident as the incident energy and/or atomic number increases. These dramatic influences also lead to a remarkable increase in the alignment parameter A20 of the residual ions, yet virtually independent of the nuclear charge for A22. The present results in Coulomb gauge and Babushkin gauge excellently agreed with each other, suggesting that there is a high degree of convergence achieved in this study. Comparison of our results with experimental data and other theoretical predictions, when available, is made.