An extensive set of fine structure levels and corresponding transition probabilities for allowed and forbidden transitions in Fe xvii is presented. A total of 490 bound energy levels of Fe xvii of total angular momenta of even and odd parities with , , , and singlet and triplet multiplicities, are obtained. They translate to over allowed (E1) transitions that are of dipole and intercombination type, and 2312 forbidden transitions that include electric quadrupole (E2), magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type representing the most detailed calculations to date for the ion. Oscillator strengths f, line strengths S, and coefficients A of spontaneous emission for the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix approximation. A-values for the forbidden transitions are obtained from atomic structure calculations using codes SUPERSTRUCTURE and GRASP. The energy levels are identified in spectroscopic notation with the help of a newly developed level identification algorithm. Nearly all 52 spectroscopically observed levels have been identified, their binding energies agreeing within 1% with our calculation. Computed transition probabilities are compared with other calculations and measurement. The effect of 2-body magnetic terms and other interactions is discussed. The present data set enhances by more than an order of magnitude the heretofore available data for transition probabilities of Fe xvii.

Aimed at solving the outstanding problem of solar opacity, and radiation transport plasma models in general, we report substantial photoabsorption in the high-energy regime due to atomic core photoexcitations not heretofore considered. In extensive $R$-matrix calculations of unprecedented complexity for an important iron ion Fe xvii (${\mathrm{Fe}}^{16+}$), with a wave function expansion of 99 Fe xviii (${\mathrm{Fe}}^{17+}$) LS core states from $n\le 4$ complexes (equivalent to 218 fine structure levels), we find (i) up to orders of magnitude enhancement in background photoionization cross sections, in addition to strongly peaked photo-excitation-of-core resonances not considered in current opacity models, and ii) demonstrate convergence with respect to successive core excitations. The resulting increase in the monochromatic continuum, and 35% in the Rosseland mean opacity, are compared with the “higher-than-predicted” iron opacity measured at the Sandia $Z$-pinch fusion device at solar interior conditions.

The online atomic database of NORAD-Atomic-Data, where NORAD stands for Nahar OSU Radiative, is part of the data sources of the two international collaborations of the Opacity Project (OP) and the Iron Project (IP). It contains large sets of parameters for the dominant atomic processes in astrophysical plasmas, such as, (i) photo-excitation, (ii) photoionization, (iii) electron–ion recombination, (iv) electron–impact excitations. The atomic parameters correspond to tables of energy levels, level-specific total photoionization cross-sections, partial photoionization cross-sections of all bound states for leaving the residual ion in the ground state, partial cross-sections of the ground state for leaving the ion in various excited states, total level-specific electron–ion recombination rate coefficients that include both the radiative and dielectronic recombination, total recombination rate coefficients summed from contributions of an infinite number of recombined states, total photo-recombination cross-sections and rates with respect to photoelectron energy, transition probabilities, lifetimes, collision strengths. The database was created after the first two atomic databases, TOPbase under the OP and TIPbase under the IP. Hence the contents of NORAD-Atomic-Data are either new or from repeated calculations using a much larger wave function expansion making the data more complete. The results have been obtained from the R-matrix method using the close-coupling approximation developed under the OP and IP, and from atomic structure calculations using the program SUPERSTRUCTURE. They have been compared with available published results which have been obtained theoretically and experimentally, and are expected to be of high accuracy in general. All computations were carried out using the computational facilities at the Ohio Supercomputer Center (OSC) starting in 1990. At present it contains atomic data for 154 atomic species, 98 of which are lighter atomic species with nuclear charge Z ≤ 28 and 56 are heavier ones with Z > 28. New data are added with publications.

The first large-scale calculations of relativistic radiative transition probabilities from the Iron Project is reported for dipole allowed and intercombination (E1) transitions in Li-like Fe XXIV and He-like Fe XXV. The ab intio calculations are carried out in the close coupling approximation using the Breit-Pauli R-matrix method in intermediate coupling characterized by SLJ, with total (2S + 1) = 2,4, L = 7, J = 1/2-11/2 even and odd parity, for Fe XXIV, and with total (2S + 1) = 1,3, L = 9, and J = 0-4 for Fe XXV. The eigenfunction expansions for the target ions include 13 levels up to the n = 3 for Fe XXV, and 16 levels up to the n = 4 for Fe XXVI, respectively. The calculated number of bound levels, 83 for Fe XXIV and 138 for Fe XXV, is much larger than experimentally observed. The level energies are in good agreement for the common levels. All dipole and intercombination fine structure transitions involving the calculated bound levels up to n = 10 and ℓ = 5 or 6 are considered. Oscillator strengths, line strengths, and Einstein A-coefficients are tabulated for 802 transitions in Fe XXIV and 2579 transitions in Fe XXV. The results compare well with limited subsets of transitions considered in previous works including fully relativistic and QED corrections. Additional comparisons between the length and the velocity formulations indicate an overall accuracy between 1-10%. The range of uncertainty is indicative of the relatively small influence of atomic effects, such as the two-body Breit interaction terms and finite nuclear mass term, that are not included in the Breit-Pauli approximation employed in the present calculations. The extensive set of data is expected to be useful in the analysis of X-ray and XUV spectra from astrophysical sources 1 .

A comprehensive study of high-accuracy photoionization cross sections is carried out using the relativistic Breit-Pauli $R$-matrix (BPRM) method for ($h\nu +\mathrm{Fe}$ xvii $\to$ Fe xviii $+e$). Owing to its importance in high-temperature plasmas, the calculations cover a large energy range, particularly the myriad photoexcitation-of-core (PEC) resonances including the $n=3$ levels not heretofore considered. The calculations employ a close-coupling wave-function expansion of 60 levels of the core ion Fe xviii ranging over a wide energy range of nearly 900 eV between the $n=2$ and $n=3$ levels. Strong-coupling effects due to dipole transition arrays $2p^5\to 2p^4(3s,3d)$ manifest themselves as large PEC resonances throughout this range and enhance the effective photoionization cross sections orders of magnitude above the background. Comparisons with the erstwhile Opacity Project (OP) and other previous calculations show that the currently available cross sections considerably underestimate the bound-free cross sections. A level-identification scheme is used for spectroscopic designation of the 454 bound fine structure levels of Fe xvii, with $n⩽10$, $l⩽9$, and $0⩽J⩽8$ of even and odd parities, obtained using the ab initio BPRM method (compared to 181 $\mathit{LS}$ bound states in the OP work). The calculated energies are compared with those available from the National Institute for Standards and Technology database, which lists 63 levels with very good agreement. Level-specific photoionization cross sections are computed for all levels. In addition, partial cross sections for leaving the core ion Fe xvii in the ground state are also obtained. These results should be relevant to modeling of astrophysical and laboratory plasma sources requiring (i) photoionization rates, (ii) extensive nonlocal-thermodynamic-equilibrium models, (iii) total unified electron-ion recombination rates including radiative and dielectronic recombination, and (iv) plasma opacities. We particularly examine PEC and non-PEC resonance strengths and emphasize their expanded role to incorporate inner-shell excitations for improved opacities, as shown by the computed monochromatic opacity of Fe xvii.