Atomic Data and Spectral Line Intensities for Fe VIII

Abstract

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Fe VIII. The configurations used are 3 p 6 3d, 3p 5 3d 2 , 3p 6 4s, 3p 6 4p, and 3 p 5 3d4s giving rise to 73 fine-structure levels in intermediate coupling. Collision strengths are calculated at four incident energies, 10, 30, 50, and 70 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of log T e (K) = 5.57, corresponding to maximum abundance of Fe VIII. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities 10 8 -10 14 cm −3 . Relative spectral line intensities are calculated. Proton excitation rates and solar blackbody radiative excitation are also included in the statistical equilibrium equations. C [2,3]. The same set of lines has also been observed by Malinovsky and Heroux [4], who measured the spectra photoelectrically using a double spectrometer flown on an Aerobee rocket. The 185.221Å line has been observed from the SERTS-95 flight [5] but it is blended with the Ni XVI line at 185.231Å. The same line has also been observed with the RES-K spectroheliograph on board the KORONAS-I satellite [6]. There are a number of unidentified lines in the recent compilation of lines observed from the UV spectrometer SUMER on SOHO [7] and it is suspected that some of these lines could be Fe VIII lines. Accurate atomic data for this ion must be available for identification of various spectral lines and to infer properties of solar and astrophysical plasmas. The presently calculated data will be useful for any present and future observations.In order to interpret data from these missions, atomic data such as energy levels, oscillator strengths, radiative transition rates, and collision strengths are required. provides all the quantities required for diagnostic purposes. In this paper we carry out a distorted wave calculation for Fe VIII in the same way as for the other Fe ions mentioned above. Since coupling between various channels is not included in the distorted wave approximation, the present calculation does not include resonances which could be important for forbidden transitions but usually not for dipole-allowed transitions for which most of the contribution to collision strengths comes from a very large number of incident partial waves.We present energy levels, oscillator strengths, radiative transition rates, and collision strengths for Fe VIII for 73 finestructure levels obtained by using the configurations 3 p 6 3d, 3 p 5 3d 2 , 3p 6 4s, 3p 6 4p, and 3 p 5 3d4s, above the Mg-like 1s 2 2s 2 2 p 6 3s 2 core. Although Fe VIII is K-like, the outermost electron is in the 3d orbital, not in the 4s orbital as in neutral potassium. Therefore, the lowest configuration is 3 p 6 3d. We solve the statistical equilibrium equations for level populations at log T e (K) = 5.57 where T e is the temperature of...

The influence of core–valence electron correlations on the convergence of energy levels and oscillator strengths of ions with an open 3d shell using Fe VIII as an example

“…However, it should be noted that there is strong mixing for many levels. The experimental [36] and the most recent theoretical results obtained by Bhatia and Eissner [26] are also shown for comparison.…”

“…CI was included between the 3s 2 3p 6 3d, 3s 2 3p 6 4d, 3s 2 3p 6 5d, 3s 2 3p 6 4s, 3s 2 3p 6 5s and 3s 2 3p 5 3d4p even configurations and the 3s 2 3p 5 3d 2 , 3s 2 3p 6 4p, 3s 2 3p 6 5p, 3s 2 3p 6 4f, 3s 2 3p 6 5f, 3s 2 3p 6 6f, 3s 2 3p 6 7f, 3s 2 3p 5 3d4s and 3s 2 3p 5 3d4d odd configurations. More recently, Bhatia and Eissner [26] reported the energy levels, oscillator strengths, radiative transition rates and collision strengths of Fe VIII for 73 fine structure energy levels obtained by including the configurations 3s 2 3p 6 3d, 3s 2 3p 5 3d 2 , 3s 2 3p 6 4s, 3s 2 3p 6 4p and 3s 2 3p 5 3d4s using the superstructure programme [27].…”

EFFECTIVE COLLISION STRENGTHS FOR ELECTRON-IMPACT EXCITATION OF Fe VIII

“…Fawcett (1989) calculated the oscillator strengths and wavelengths for lines belonging to the transition arrays from the ground state to the 3p 5 3d 2 , 3p 6 nl, and 3p 5 3d4s levels using extensive multiconfiguration expansions. More recently, Bhatia & Eissner (2000) reported the energy levels, oscillator strengths, radiative transition rates, and collision strengths of Fe viii for 73 finestructure energy levels of the 3p 6 3d, 3p 5 3d 2 , 3p 6 4s, 3p 6 4p, and 3p 5 3d4s configurations using the SUPERSTRUCTURE program (Eissner et al 1972). All past calculations in both LS and intermediate-coupling scheme have not considered the important 3p-3d inter-shell core-valence electron correlation effects.…”

“…As concerned the electron scattering calculation, earlier distorted-wave and close-coupling calculations for Fe viii (Pindzola et al 1988;Bhatia & Eissner 2000) included only a small number of configurations and did not map out the rich resonance structure found near excitation thresholds. The most up to date and the most extensive electron scattering calculations for Fe viii ion have been provided by Griffin et al (2000).…”

Soft X-ray emission lines of Fe VII-Fe XVI in stellar coronae in the range 49-106 Å

“…For example, Witthoeft & Badnell (2008) calculated the electron‐impact excitation of Fe 6+ with the intermediate‐coupling frame transformation (ICFT) R ‐matrix method, and extended the excitation data to levels of the 3p 6 3d5p configuration. For Fe 7+ , Griffin et al's data (2000) have been incorporated into the chianti 5 package (Landi et al 2006), the data being more accurate than the DW results of Bhatia & Eissner (2000). For Fe 9+ , Pelan & Berrington (2001) generated the excitation data among the 31 lowest‐lying fine‐structure levels using a 180‐level (target) Breit–Pauli R ‐matrix calculation.…”