High-resolution measurement of the dielectronic recombination of fluorinelike selenium ions

We have measured the dielectronic recombination cross section of Se25+ ions at center-of-mass energies from 1 to 1800 eV using merged electron and ion beams in the Heidelberg heavy-ion Test Storage Ring (TSR). All dielectronic resonances involving changes of Delta N = 0 and Delta N = 1 of the core principal quantum number N are covered with high-energy resolution (ranging from <0.6 eV at <90 eV to approximate to 6 eV at 1600 eV). A strong contribution of Delta N = 1 Rydberg resonances at 1200-1700 eV is observed. The results are compared with isolated-resonance intermediate-coupling calculations of the cross section. Good agreement is found for the Delta N = 0 and the low-lying Delta N = 1 resonances. For the Delta N = 1 Rydberg series the resonant pattern continues to be well reproduced by theory, whereas the total energy-integrated cross section significantly exceeds the theoretical prediction. From experimental and theoretical results rate coefficients for isotropic plasma temperatures between 100 and 2000 eV are also derived.