Fine-structure Collision Strengths Research Articles

Electron-impact Excitation of Fe i

Abstract The Fe i spectra emitted by astrophysical sources contain information on plasma parameters such as chemical abundances and magnetic fields. However, to determine these parameters requires detailed plasma modeling, which in turn needs accurate atomic data for processes such as radiative decay and electron-impact excitation in Fe i. A lack of fine-structure resolved collision strengths for transitions in Fe i is addressed in this paper with the presentation of data obtained from a Dirac R-matrix calculation. The suitability of our choice of target description is shown, with our energies generally within 7% of literature values. Various A-values are compared with other theoretical and experimental results, and the quality of the collision strengths produced in this work demonstrated. A comparison of 300- and 1000-level close-coupling expansions is made, the latter shown to eliminate pseudoresonances in the collision strengths at electron energies between 0.5 and 1.0 Ry. Maxwell-averaged effective collision strengths are presented, and the convergence of our data is shown in the temperature range 1000–100,000 K.

Calculations of the Atomic Structure for Fe XVII Lines

Energy levels, line strengths, oscillator strengths, radiative decay rates and fine structure collision strengths are presented for sixteen-times ionized iron (Fe XVII). The atomic data are calculated with the AUTOSTRUCTURE code, where relativistic corrections are introduced according to the Breit–Pauli distorted wave approach. The calculations of atomic data for 89 fine-structure levels generated from eleven configurations 2s2p, 2s2p (3s, 3p, 3d), 2s2p (4s, 4p, 4d, 4f) and 2s2p (3s, 3p, 3d) of the Ne-like Fe ion are presented. Fine structure collision strengths for transitions from the ground and the first four excited levels are presented at four electron energies: 75, 125, 175, and 250 Ry. These atomic structure data are compared with the available experimental and theoretical results.

Energy levels, oscillator strengths, radiative decay rates and fine structure collision strengths for Ar IX lines

Energy levels, line strengths, oscillator strengths, radiative decay rates and fine structure collision strengths are presented for eight-time ionized iron (Ar IX). The atomic data are calculated with the AUTOSTRUCTURE code, where relativistic corrections are introduced according to the Breit–Pauli distorted wave approach. The calculations of atomic data for 37 fine-structure levels generated from seven configurations 2s22p6, 2s22p5 (3s, 3p, 3d) and 2s12p6 (3s, 3p, 3d) of the Ne-like Ar ion are presented. Fine structure collision strengths for transitions from the ground and the first four excited levels are presented at four electron energies 75, 125, 175 and 250Ryd. These atomic structure data with the available experimental and theoretical results are compared.

Energy levels, oscillator strengths, radiative decay rates, and fine-structure collision strengths for the Zn-like ions Nb XII and Mo XIII

Energy levels, line strengths, oscillator strengths, radiative decay rates, and fine-structure collision strengths are presented for the Zn-like ions Nb XII and Mo XIII. The atomic data are calculated with the AUTOSTRUCTURE code, where relativistic corrections are introduced according to the Breit–Pauli distorted wave approach. We present the calculations of atomic data for 110 fine-structure levels generated from fifteen configurations (1s22s22p63s23p63d10)4s2, 4s4p, 4p2, 4s4d, 4s4f, 4s5s, 4p4d, 4s5p, 4s5d, 4p4f, 4p5s, 4d2, 4d4f, 4f2, and 3d94s24p. Fine-structure collision strengths for transitions from the ground and the first four excited levels are presented at six electron energies (20, 50, 80, 110, 150, and 180 Ryd). Our atomic structure data are compared with the available experimental and theoretical results.

Structural and collisional data for Mg III and Al IV

We present in this work energy levels, oscillator strengths, radiative decay rates and fine structure collision strengths for the Mg III and Al IV ions. The 11 configurations: (1s2) 2s22p6, 2s22p53l, 2s2p63l, 2s22p54l (l⩽n-1, where n is the principal quantum number), yielding the lowest 75 levels are used. The collisional data for these two ions are missing in the literature, especially the database CHIANTI, this is the principal motivation behind the present work. Calculations have been performed using the AUTOSTRUCTURE code. AUTOSTRUCTURE treats the scattering problem in the distorted wave approach. Fine structure collision strengths are calculated for a range of electron energies from 10Ry to 240Ry. The atomic structure data are compared to available experimental and theoretical results.

Fine-structure collision strengths and line ratios for [Ne v] in infrared and optical sources

New collisions’ strengths for the mid-infrared (mid-IR) and optical transitions in Ne v are presented. Breit–Pauli-R-Matrix calculations for electron impact excitation are carried out with fully resolved near-threshold resonances at very low energies. In particular, the fine-structure lines at 14 and 24 μm due to transitions among the ground state levels 1s22s22p3 3P0, 1, 2, and the optical/near-ultraviolet lines at 2973, 3346 and 3426 Å transitions among the 3P0, 1, 2, 1D2, 1S0 levels are described. Maxwellian-averaged collision strengths are tabulated for all forbidden transitions within the ground configuration. While some significant differences are found for both the far infrared and the optical transitions compared to previous results, computed line emissivity ratios are in good agreement, but change rapidly in the low temperature range Te < 10 000 K. An analysis of the 14/24 μm ratio in low-energy-density (LED) plasma conditions reveals considerable variation; the effective rate coefficient may be dominated by the very low energy behaviour rather than the Maxwellian-averaged collision strengths. Computed values suggest a possible solution to the anomalous mid-IR ratios found to be lower than theoretical limits observed from planetary nebulae and Seyfert galaxies. While such LED conditions may be present in infrared sources, they might be inconsistent with photoionization equilibrium models.

Energy levels, oscillator strengths, radiative decay rates, and fine structure collision strengths for Kr VII lines

Energy levels, line strengths, oscillator strengths, radiative decay rates and fine structure collision strengths are presented for six-times ionized krypton (Kr VII). The atomic data are calculated with the AUTOSTRUCTURE code, where relativistic corrections are introduced according to the Breit–Pauli distorted wave approach. We present calculations of atomic data for 40 fine-structure levels generated from nine configurations ((1s22s22p63s23p63d10)4s2, 4lnl′, n = 4, 5; l = 0, 1; and l′ ≤ 3) of the Zn-like Kr ion. Fine structure collision strengths for transitions from the ground and the first four excited levels are presented at six electron energies: 8, 15, 30, 45, 60, and 80 Ryd. Our atomic structure data are compared with the available experimental and theoretical results.

Radiative atomic data and fine-structure collision strengths for neon-like sulfur

We have employed the distorted wave method to calculate radiative and collisional atomic data for the neon-like sulfur S VII. Fine-structure collision strengths have been calculated at many energy values.

Fine structure collision strengths for S VII lines

Energy levels, oscillator strengths, radiative decay rates and fine structure collision strengths are presented for six times ionized sulfur S VII. The atomic data are calculated with the SUPERSTRUCTURE code, where relativistic corrections are introduced according to the Breit–Pauli approach. We include in this work the (1s2) 2s22p6, 2s22p53l, 2s2p63l, 2s22p54l (l ⩽ n − 1) configurations that yield the lowest 75 levels. The scattering problem is treated in the distorted wave approach by the code DISTORTED WAVE. This produces collision strengths in LS coupling that will be used by the code JAJOM to transform them into fine structure ones. Fine structure collision strengths for transitions from the ground and the first four excited levels are presented at six electron energies from 20 to 120 Ryd by a step of 20 Ryd. Our atomic structure data are compared with the available experimental and theoretical results.

Electron impact excitation rate coefficients of N II ion

This paper calculates the electron impact excitation rate coefficients from the ground term 2s22p2 3P to the excited terms of the 2s22p2, 2s2p3, 2s22p3s, 2s22p3p, and 2s22p3d configurations of N II. In the calculations, multiconfiguration Dirac–Fork wave functions have been applied to describe the target-ion states and relativistic distorted-wave calculation has been performed to generate fine-structure collision strengths. The collision strengths are then averaged over a Maxwellian distribution of electron velocities in order to generate the effective collision strengths. The calculated rate coefficients are compared with available experimental and theoretical data, and some good agreements are found for the outer shell electron excitations. But for the inner shell electron excitations there are still some differences between the present calculations and available experiments.

Radiative transition rates and collision strengths for Si II

Aims. This work reports radiative transition rates and electron impact excitation collision strengths for levels of the 3s23p, 3s3p2, 3s24s, and 3s23d configurations of Siii. Methods. The radiative data were computed using the Thomas-Fermi-Dirac-Amaldi central potential, but with the modifications introduced by Bautista (2008) that account for the effects of electron-electron interactions. We also introduce new schemes for the optimization of the variational parameters of the potential. Additional calculations were carried out with the Relativistic Hartree-Fock and the multiconfiguration Dirac-Fock methods. Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method which accounts for spin-orbit coupling effects. Results. We present extensive comparisons between the results of different approximations and with the most recent calculations and experiment available in the literature. From these comparisons we derive a recommended set of gf- values and radiative transition rates with their corresponding estimated uncertainties. We also study the effects of different approximations in the representation of the target ion on the electron-impact collision strengths. Our most accurate set of collision strengths were integrated over a Maxwellian distribution of electron energies and the resulting effective collision strengths are given for a wide range of temperatures. Our results present significant differences from recent calculations with the B-spline non-orthogonal R-matrix method. We discuss the sources of the differences.

Fine structure effective collision strengths for the electron impact excitation of

Electron impact excitation collision strengths are required for the analysis and interpretation of stellar observations. To date no evaluations exist for the ion. An 18-state R-matrix calculation has been performed. The target states are represented by configuration interaction wavefunctions and consist of the 18 lowest LS states, having configurations 3s23p3, 3s3p4 and 3s23p23d. These target states give rise to 39 fine structure levels and 741 possible transitions. The fine structure collision strengths were obtained by transforming to a jj-coupling scheme using the JAJOM program of Saraph and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of velocities. The nonzero effective collision strengths for transitions between the fine structure levels are given for electron temperatures (Te) in the range log10 Te(K)=4.5–6.5. Data for transitions among the five fine structure levels arising from the 3s23p3 ground state configurations are considered in some detail in this paper. These calculations are the first evaluations of collision strengths and effective collision strengths for this ion.

Fine structure effective collision strengths for the electron impact excitation of the sulphur ion S V

We have performed a 14-state R-matrix calculation to determine effective collision strengths for fine structure transitions in S v ion. The target states were taken to be the 14 lowest LS states, which involve configurations of the form - (2p6)3s2, 3s3p, 3p2, 3s3d, 3s4s, 3p3d. These target states give rise to 26 fine structure levels and 325 possible transitions. The fine structure collision strengths were obtained by transforming to a jj-coupling scheme using the JAJOM program of Saraph and using a sufficiently fine energy mesh so that the resonance structure can be be properly delineated. Effective collision strengths were calculated by averaging the electron collision strengths over a Maxwellian distribution of velocities. Comparisons are made with an earlier R-matrix calculation and with a distorted-wave approximation.

Relativistic and correlation effects in electron impact excitation of forbidden transitions of OII

We investigate relativistic and correlation effects in electron impact excitation of singly ionized oxygen using the Breit–Pauli R-matrix method. The intermediate coupling close-coupling calculations are carried out using a 16-level target representation dominated by the electronic configurations 1s22s22p3, 1s22s2p4, 1s22s22p23s. Resonance structures are delineated in detail to ascertain the effect on averaged collision strengths. Convergence of the partial wave summation is ensured for non-dipole transitions in the R-matrix calculations. The present results differ significantly from the similar Breit–Pauli R-matrix calculations by McLaughlin and Bell (1998 J. Phys. B: At. Mol. Opt. Phys. 31 4317–29), but are essentially in agreement with the LS coupling results of Pradhan (1976a J. Phys. B: At. Mol. Opt. Phys. 9 433–43, 1976b Mon. Not. R. Astron. Soc. 177 31–8). A comprehensive study of the detailed energy behaviour of all forbidden transitions among the five levels of the ground configuration, i.e. 2s2p3(4So3/2, 2Do5/2,3/2, 2Po3/2,1/2) shows that the finestructure collision strengths do not significantly depart from the values obtained from a purely transformation, and relativistic effects are therefore small. We find that the Maxwellian-averaged effective collision strengths for the ten transitions also differ from the previous work, most likely due to more extensive delineation of resonances in the present work. However, the differences are largely systematic and therefore the OII line intensity ratios are not significantly affected. We also obtain an excellent agreement between the present-calculated cross sections for the 4So − 2Do transition and the experimental merged beam measurements.

Fine structure effective collision strengths for the electron impact excitation of Al III

Context. $\ion{S}{v}$ emission lines have been observed in solar flares, solar upper atmospheres, quiet sun regions and broad band absorption line quasars, with particular lines being used as diagnostics for electron temperature and density. Accurate atomic data are needed to analyse the observational data and to date the best available calculations for this ion have not included contributions from resonances. Aims. To calculate fine structure effective collision strengths for the electron impact excitation of $\ion{S}{v}$ using a method which incorporates resonances. Methods. A 14-state R -matrix calculation has been performed. The target states are represented by configuration interaction wavefunctions and consist of the 14 lowest LS states, having configurations (2p 6 )3s 2 , 3s3p, 3p 2 , 3s3d, 3s4s, 3p3d. These target states give rise to 26 fine structure levels and 325 possible transitions. The fine structure collision strengths were obtained by transforming to a jj -coupling scheme using the JAJOM program of Saraph and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. The effective collision strengths were calculated by averaging the electron collision strengths over a Maxwellian distribution of velocities. Results. Tabulations of the non-zero effective collision strengths for transitions between both the LS states and the fine structure levels are given for electron temperatures ( T e ) in the range $\log_{10} T_{\rm e} ({\rm K}) = 4.0{-}6.0$. Comparisons are made with previous R -matrix and distorted-wave calculations.

Atomic data from the Iron project

This paper reports on radiative transition rates and electron impact excitation rate coefficients for levels of the 3d 7 ground configuration of Ni IV. The radiative data were computed using the Thomas-Fermi-Dirac central potential method, which allows for configuration interactions (CI) and relativistic effects in the Breit-Pauli formalism. Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method that accounts for spin-orbit coupling effects. The collision strengths were integrated over a Maxwellian distribution of electron energies, and the resulting effective collision strengths are given for a wide range of temperatures. We build a multilevel model for the Ni IV system and use it to identify the most important lines in optical and infrared spectra and to compute line ratios as diagnostics of nebular conditions. Finally, we test these data against recent observations of the bipolar planetary nebula Mz 3.

Effective collision strengths for fine-structure transitions for the electron impact excitation of N II

We present effective collision strengths for the electron impact excitation of singly ionized nitrogen which have been calculated using the R-matrix method. The 23 lowest LS states are included in the expansion of the total wavefunction. These target states arise from the 2s 2 2p 2 ,2 s2p 3 and 2s 2 2p3l(l = s, p, d) configurations, leading to 41 fine structure levels and 820 possible transitions. The fine-structure collision strengths were obtained by transforming to a jj-coupling scheme using the JAJOM program of Saraph and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. The effective collision strengths were calculated by averaging the electron collision strengths over a Maxwellian distribution of velocities. Tabulations of the non-zero effective collision strengths are given for electron temperatures (Te )i n the range log10 Te(K) = 2.0−5.5.

Calculated Rate Coefficients for the Electron Impact Excitation of Singly Ionized Nitrogen

A 23-state R-matrix calculation has been performed to generate finestructure collision strengths for the electron impact excitation of N II. The target states are represented by configuration interaction wavefunctions and consist of the set of configurations having the form 2s22p2, 2s2p3, 2s22p3l (l = s,p,d). The fine structure collision strengths are generated by transforming to a jj-coupling scheme using the JAJOM program of Saraph, and a sufficiently fine energy mesh has been used to properly delineate the resonance structure. The collision strengths are then averaged over, using a Maxwellian distribution of velocities in order to generate the effective collision strengths. In this paper we use our data to calculate the excitation rate coefficients for six LS transitions so that comparison can be made with experimental and theoretical data presented in Frost et al. The transitions involved are those from the ground state to the 2s22p3s 1Po, 2s2p31Do, 2s22p3p 3Se, 2s2p33So, 2s22p3d 3Do and 2s22p3d 3Po levels, and involve 30 fine-structure levels. The theoretical calculation detailed by Frost et al (also a 23 state R-matrix calculation) produces effective collision strengths for transitions between LS levels, and the authors note `good agreement' with an earlier 13-state R-matrix calculation by Stafford et al. The current calculation improves upon the work of Stafford et al and provides much more data, allowing for comparisons to be made with transitions not included by Stafford et al. In general we find that the current calculation is in better agreement with the calculation described in Frost et al than with that of Stafford et al, and that our calculation provides the same `broad trend' of agreement with the Frost et al experimental rates.

12C/13C Ratio in Planetary Nebulae from theIUEArchives

We investigated the abundance ratio of 12C/13C in planetary nebulae by examining emission lines arising from C III 2s2p 3P → 2s2 1S0. Spectra were retrieved from the International Ultraviolet Explorer archives, and multiple spectra of the same object were co-added to achieve improved signal-to-noise ratio. The 13C hyperfine structure line at 1909.6 A was detected in NGC 2440. The 12C/13C ratio was found to be ~4.4 ± 1.2. In all other objects, we provide an upper limit for the flux of the 1910 A line. For 23 of these sources, a lower limit for the 12C/13C ratio was established. The impact on our current understanding of stellar evolution is discussed. The resulting high-signal-to-noise ratio C III spectrum helps constrain the atomic physics of the line formation process. Some objects have the measured 1907/1909 A flux ratio outside the low-electron density theoretical limit for 12C. A mixture of 13C with 12C helps to close the gap somewhat. Nevertheless, some observed 1907/1909 A flux ratios still appear too high to conform to the currently predicted limits. It is shown that this limit, as well as the 1910/1909 A flux ratio, are predominantly influenced by using the standard partitioning among the collision strengths for the multiplet 1S0-3P according to the statistical weights. A detailed calculation for the fine-structure collision strengths between these individual levels would be valuable.

Effective collision strengths for transitions in singly ionized nitrogen

The R-matrix method has been used to calculate effective collision strengths for the electron-impact excitation of the carbon-like ion N II. The lowest 23 LS target states are included in the expansion of the total wavefunction, consisting of the nine n = 2 states with configurations 2 s 22p 2 and 2s2p 3 , along with 14 n = 3 states with configuration 2s 2 2p3l (l= s,p,d). The fine-structure collision strengths have been obtained by transforming to a jj-coupling scheme using Saraph's JAJOM program, and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. Effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities. Results are presented for transitions among the 2s 2 2p 2 3 P, 1 D, 1 S and 2s2p 3 5 S levels for electron temperatures in the range log T e (K) = 2.0-5.1, appropriate for astrophysical applications.