Electron-electron interaction studied in strong central fields by resonant transfer and excitation with H-like U ions

Electron-electron interaction is studied in the strongest possible atomic fields (Z{alpha} >>1) in the presence of only two electrons. A quasifree electron from a hydrogen gas target is resonantly captured into an L{sub j} subshell of a fast H-like U{sup 91+} ion by simultaneous excitation of the strongly bound K electron also into an L{sub j{sup '}} subshell of the projectile, with j and j{sup '} the total angular momenta of 1/2 or 3/2 for the electron of concern. This resonant transfer and excitation process (RTE) KL{sub j}L{sub j{sup '}} is mediated by electron-electron interaction. It is equivalent to dielectronic recombination in ion-electron collisions and leads to a doubly excited He-like U{sup 90+**} ion, which stabilizes--almost exclusively--via the emission of two successive K x rays, first a K hypersatellite (K{alpha}{sub i}-H) and then a K satellite (K{alpha}{sub i{sup s}}-S) transition. The K x-ray emission characteristics associated with one-electron capture in collisions of U{sup 91+} ions with a hydrogen target are studied for the three resonance groups of the KL{sub j}L{sub j{sup '}} RTE and one off-resonance energy, i.e., in the energy range between 100 and 135 MeV/u. The total cross section for the first resonance group KL{sub 1/2}L{sub 1/2} confirmsmore » the importance of the Breit contribution to the interaction. The angular distribution for the K{alpha}{sub 2}-H transition (j=1/2) is isotropic in the projectile system, whereas the K{alpha}{sub 1}-H transition (j=3/2) indicates a strong alignment for the 3/2 electrons in the doubly excited states for the second resonance group KL{sub 1/2}L{sub 3/2}. The experimental results are in agreement with fully relativistic calculations including the generalized Breit interaction.« less