Relativistic close-coupling calculations for photoionization and recombination of Ne-like Fe XVII

Relativistic and channel coupling effects in photoionization and unified electronic recombination of Fe XVII are demonstrated with an extensive 60-level close-coupling calculation using the Breit-Pauli R-matrix method. A multiconfiguration eigenfunction expansion up to the n53 levels of the core ion Fe XVIII is employed with five spectroscopic configurations 2s2p,2s2p,2s2p 3s ,3p ,3d , and a number of correlation configurations. The unified e1ion recombination calculations for e1Fe XVIII→Fe XVII include both the nonresonant and resonant recombination ~‘‘radiative’’ and ‘‘dielectronic recombination’’—RR and DR!. Photoionization and e 1ion recombination calculations are carried out for the total and the level-specific cross sections, including the ground and several hundred excited bound levels of Fe XVII ~up to fine-structure levels with n510). The low-energy and the high-energy cross sections are compared from ~i! a three-level calculation including only the 2sp (P1/2,3/2 o ) and 2s2p (S1/2) levels of Fe XVIII, and ~ii! the first 60-level calculation with Dn.0 coupled channels. Strong channel coupling effects are demonstrated throughout the energy ranges considered, in particular via giant photoexcitation-of-core ~PEC! resonances due to L-M shell dipole transition arrays 2p5→2p4 3s ,3d in Fe XIII that enhance effective cross sections by orders of magnitude. Comparison is made with previous theoretical and experimental works on photoionization and recombination that considered the relatively small low-energy region ~i!, and the weaker Dn50 couplings. While the simpler three-level results describe the near-threshold photoionization and recombination, they are inadequate for practical applications that also require the higher-energy cross sections for modeling ionization balance of Fe XVII in laboratory and astrophysical plasmas. The present 60-level results should provide reasonably complete and accurate datasets for both photoionization and e1ion recombination of Fe XVII.