Triply excited states in dielectronic recombination with excited He-like uranium

We study process of dielectronic recombination with He-like uranium initially being in one of the metastable states $[{\left(1s2s\right)}_0$ and ${\left(1s2p_{1/2}\right)}_0]$. We consider resonant regions of the incident electron energy corresponding to participation of triply excited states of Li-like uranium. The total and differential cross sections for dielectronic recombination as well as the energies and widths of the autoionizing states are calculated accurately within the QED theory. The cross section of the considered process is comparable in order of magnitude with the cross section of dielectronic recombination with H-like or He-like uranium initially being in the ground states. We investigated the contribution of the Breit interaction to the cross section; in particular, we found that the Breit interaction may both significantly increase and decrease the cross section.

Figure 1

Total cross sections (in kbarn) for dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2s\right)}_0$ (the top panel) and with ${\mathrm{U}}^{90+}{\left(1s2p_{1/2}\right)}_0$ (the bottom panel) as a function of incident-electron kinetic energy. The solid curves present calculations with full electron-electron interaction. The dotted curves present calculations where only Coulomb interaction is taken into account.

Figure 2

Total cross section for dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2p_{1/2}\right)}_0$. The energy region corresponds to the significant participation of ${\left(2s^{2}2p_{1/2}\right)}_{1/2}$ and ${\left(2s2p_{1/2}^2\right)}_{1/2}$ states. The black solid curve denotes the accurate QED calculation where full interelectron interaction is taken into account. The red dotted curve corresponds to the calculation where only Coulomb interaction is taken into account and the blue dashed curve corresponds to the calculation without retardation in the Breit part of the interelectron interaction.

Figure 3

Differential cross sections (in barn/sr) for dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2s\right)}_0$ as a function of incident-electron kinetic energy and polar angle of emitted photon. The left column presents calculations with full electron-electron interaction and the right column presents calculations where only Coulomb interaction is taken into account.

Figure 4

Differential cross sections (in barn/sr) for dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2p_{1/2}\right)}_0$ as a function of incident-electron kinetic energy and polar angle of emitted photon. The left column presents calculations with full electron-electron interaction and the right column presents calculations where only Coulomb interaction is taken into account.

Figure 5

The relative contribution of the higher multipoles of the emitted photon to the differential cross section of dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2s\right)}_0$ [see Eq. (14)].

Figure 6

The Stokes parameters for the dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2s\right)}_0$. The first and second rows correspond to the parameters $P_1$ and $P_2$, respectively [see Eqs. (15) and (16)]. The third row presents the Stokes parameter for circular polarization $P_3$ [see Eq. (17)]. The left and right columns correspond to the calculations with and without Briet interelectron interaction, respectively.

Figure 7

Same as in Fig. 6, but for the dielectronic recombination with ${\mathrm{U}}^{90+}{\left(1s2p_{1/2}\right)}_0$.