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

We have measured the dielectronic recombination cross section of Se^25+ 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 =0 and =1 of the core principal quantum number N are covered with high-energy resolution (ranging from 0. 6 eV at 90 eV to 6 eV at 1600 eV). A strong contribution of =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 =0 and the low-lying =1 resonances. For the =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. 1996 The American Physical Society.