X-ray emission from highly charged ions following dielectronic recombination: relativistic effects upon angular distributions and polarization

The angular distribution and polarization properties are reviewed for the x-ray emission from highly charged ions following dielectronic recombination (DR). Emphasis is placed on how these properties in the decay of (doubly) excited states are affected by relativity, e. g. the relativistic terms of the electron-electron interaction and the multipoles of the radiation field other than the electric-dipole (E1) component. For isolated DR resonances, it is shown that the Breit interaction, as the dominant correction to the Coulomb repulsion, may change the angular emission pattern qualitatively, from a preferred emission along the beam axis towards one that is dominant perpendicular to the beam, or vice versa. Moreover, the interference between the leading E1 and other electric and magnetic multipoles may significantly alter the angular distribution and polarization of the emitted x-rays.