Dielectronic recombination of lithiumlike Ni25+ ions: High-resolution ratecoefficients and influence of external crossed electric and magnetic fields - art. no. 022708

Absolute dielectronic recombination (DR) rates for lithiumlike Ni25+(1s(2)2 s) ions were measured at high-energy resolution at the Heidelberg heavy-ion storage ring TSR. We studied the center-of-mass energy range 0-130 eV whic h covers all Delta n = 0 core excitations. The influence of external crosse d electric (0-300 V/cm) and magnetic (41.8-80.1 mT) fields was investigated . For the measurement at near-zero electric field, resonance energies and s trengths are given for Rydberg levels up to n = 32; also Maxwellian plasma rate coefficients for the Delta n = 0 DR at electron temperatures between 0 .5 and 200 eV are provided. For increasing electric-field strength we find that for both the 2p(1/2) and 2p(3/2) series of Ni24+(1s(2)2p(j)nl) Rydberg resonances with n > 30, the DR rate coefficient increases approximately li nearly by up to a factor of 1.5. The relative increase due to the applied e lectric field for Ni25+ is remarkably lower than that found in previous mea surements with lighter isoelectronic Si11+, Cl14+, and Ti19+ ions [T. Barts ch et al., Phys. Rev. Lett. 79, 2233 (1997); 82, 3779 (1999); J. Phys. B 33 , L453 (2000)], and in contrast to the results for lighter ions no clear de pendence of the electric-field enhancement on the magnetic-held strength is found. The Maxwellian plasma rate coefficients for Delta n = 0 DR of Ni25 are enhanced by at most 11% in the presence of the strongest experimentall y applied fields.