Electron excitation of Ca XVII

Electron-excitation collision strengths have been calculated for transitions between the ten lowest levels of Ca XVII (2sS, 2s2p P, 2s2p P, 2pP 2p D, 2pS ). At high impact energies, where all the channels are open, the calculation was carried out in the LS-coupling approximation by means of the R-matrix method. Transitions between the fine structure levels were then determined by application of a unitary transformation to the LS-coupled K-matrices. At low impact energies, where some of the channels may be closed, an extension of the R-matrix method was employed to take account of relativistic effects directly in the scattering equations. In general, results are in good agreement with recent distorted-wave calculations. Electron-excitation rates are given for a range of electron temperatures.

Energy levels, radiative rates and electron impact excitation rates for transitions in Be-like Cl XIV, K XVI and Ge XXIX

Results for energy levels, radiative rates and electron impact excitation (effective) collision strengths for transitions in Be-like Cl XIV, K XVI and Ge XXIX are reported. For the calculations of energy levels and radiative rates the general-purpose relativistic atomic structure package is adopted, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code is used. Oscillator strengths, radiative rates and line strengths are listed for all E1, E2, M1 and M2 transitions among the lowest 98 levels of the n ≤ 4 configurations. Furthermore, lifetimes are provided for all levels and comparisons made with available theoretical and experimental results. Resonances in the collision strengths are resolved in a fine energy mesh and averaged over a Maxwellian velocity distribution to obtain the effective collision strengths. Results obtained are listed over a wide temperature range up to 10^7.8 K, depending on the ion.

Energy levels, radiative rates and electron impact excitation rates for transitions in Fe XIV

Energies and lifetimes are reported for the lowest 136 levels of Fe XIV, belonging to the (1s(2)2s(2)2p(6)) 3s(2)3p, 3s(3)p(2), 3s(2)3d, 3p(3), 3s(3)p(3)d, 3p(2)3d, 3s(3)d(2), 3p(3)d(2) and 3s(2)4l configurations. Additionally, radiative rates, oscillator strengths and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions. Theoretical lifetimes determined from these radiative rates for most levels show satisfactory agreement with earlier calculations, a swell as with measurements. Electron impact excitation collision strengths are also calculated with the Dirac atomic R-matrix code (DARC) over a wide energy range up to 260 Ryd. Furthermore, resonances have been resolved in a fine energy mesh to determine effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron velocities. Results are listed for all 9180 transitions among the 136 levels over a wide range of electron temperatures, up to 10(7.1) K. Comparisons are made with available results in the literature, and the accuracy of the present data is assessed.

Non-equilibrium modeling of the FE XVII 3C/3D Line Ratio in an Intense X-ray Free-electron Laser Excited Plasma

Recent measurements using an X-ray Free Electron Laser (XFEL) and an Electron Beam Ion Trap at the Linac Coherent Light Source facility highlighted large discrepancies between the observed and theoretical values for the Fe XVII 3C/3D line intensity ratio. This result raised the question of whether the theoretical oscillator strengths may be significantly in error, due to insufficiencies in the atomic structure calculations. We present time-dependent spectral modeling of this experiment and show that non-equilibrium effects can dramatically reduce the predicted 3C/3D line intensity ratio, compared with that obtained by simply taking the ratio of oscillator strengths. Once these non-equilibrium effects are accounted for, the measured line intensity ratio can be used to determine a revised value for the 3C/3D oscillator strength ratio, giving a range from 3.0 to 3.5. We also provide a framework to narrow this range further, if more precise information about the pulse parameters can be determined. We discuss the implications of the new results for the use of Fe XVII spectral features as astrophysical diagnostics and investigate the importance of time-dependent effects in interpreting XFEL-excited plasmas.