Calculations Of Collision Strengths Research Articles

Comment on “Atomic structure and electron impact excitation of Al-like ions (Ga–Br)” by HB Wang and G Jiang in At. Data Nucl. Data Tables 148 (2022) 101532

In a recent paper, Wang and Jiang (At. Data Nucl. Data Tables 148 (2022) 101532) have reported data for energy levels, radiative rates (A-values), and effective collision strengths (Υ) for some transitions of five Al-like ions, namely Ga XIX, Ge XX, As XXI, Se XXII, and Br XXIII. On a closer examination we find that their reported data for energy levels and A-values are generally correct, but not for Υ. Their Υ values, for all transitions (allowed or forbidden) and for all ions, invariably decrease at higher temperatures. This is mainly because they have adopted a limited range of electron energies for the calculations of collision strengths. We demonstrate this with our calculations with the Flexible Atomic Code (FAC), and conclude that their Υ values are inaccurate, unreliable, and should not be adopted in any applications or modelling analysis.

Biosignature line ratios of [P ii] in exoplanetary and nebular environments

ABSTRACT Being the backbone element of deoxyribonucleic acid, phosphorus is a key component in the search for life in the Universe. To aid in its detection, we present line emissivity ratios for the five lowest-lying forbidden [P ii] transitions, namely those among the levels 3s23p2(3P0, 3P1, 3P2, 1D2, and 1S0). The wavelengths range between 0.44 and 70 µm, and several lie within the spectroscopic domain observable with the JWST. These line ratios have been calculated using a new collisional-radiative-cascade (CRR) model combining calculated collision strengths and level-specific recombination rate coefficients, with both data sets computed using the accurate Breit–Pauli R-matrix method. The CRR model includes a new scheme for (e + ion) recombination to emission-line formation. We compare its effect to models incorporating only electron-impact excitation and spontaneous radiative decay. We find that (e + ion) recombination has a significant impact on all line ratios, and represents a major improvement in physical accuracy of emission-line models.

Effective Collision Strengths and Radiative Parameters for Lines in the Sc ii Spectrum

Abstract This work reports large-scale calculations of electron excitation effective collision strengths and transition rates for a wide range of Sc ii spectral lines for astrophysical analysis and modeling. The present results are important for reliable abundance determinations in various astrophysical objects, including metal-poor stars, H ii regions, and gaseous nebulae. Accurate descriptions of the target wave functions and adequate accounts of the various interactions between the target levels are of primary importance for calculations of collision and radiative parameters. The target wave functions have been determined by a combination of the multiconfiguration Hartree–Fock and B-spline box-based close-coupling methods, together with the nonorthogonal orbitals technique. The calculations of the collision strengths have been performed using the B-spline Breit–Pauli R-matrix method. The close-coupling expansion includes 145 fine-structure levels of Sc ii belonging to the terms of the 3p 63d 2, 3p 63d4l (l = 0–3), 3p 63d5l (l = 0–3), 3p 63d6s, 3p 64s 2, 3p 64s4l (l = 0–3), 3p 64s5l (l = 0–1), and 3p 64p 2 configurations. The effective collision strengths are reported as a function of electron temperature in the range from 103 to 105 K. The collision and radiative rates are reported for all of the possible transitions between the 145 fine-structure levels. Striking discrepancies exist with the previous R-matrix calculations of the effective collision strengths for the majority of the transitions, indicating possible systematic errors in these calculations. Thus, there is a need for accurate calculations to reduce the uncertainties in the atomic data. The likely uncertainties in our effective collision strengths and radiative parameters have been assessed by means of comparisons with other collision calculations and available experimental radiative parameters.

R-matrix electron-impact excitation data for the O-like iso-electronic sequence

Context. Astrophysical plasma codes are built on atomic databases. In the current atomic databases, R-matrix electron-impact excitation data of O-like ions are limited. The accuracy of plasma diagnostics with O-like ions depends on the availability and accuracy of the atomic data. This is particularly relevant in the context of future observatories equipped with the next generation of high-resolution spectrometers. Aims. We aim to obtain level-resolved effective collision strengths of O-like ions from Ne III to Zn XXIII (i.e. Ne2+ to Zn22+) over a wide range of temperatures. This includes transitions up to nl = 5d for each ion. We also aim to assess the accuracy of the new data, as well as their impact on solar atmosphere plasma diagnostics, compared to those available within the CHIANTI database. Methods. Large-scale R-matrix intermediate coupling frame transformation calculations were performed systematically for the O-like iso-electronic sequence. For each ion, 630 fine-structure levels were included in both the configuration interaction target and close-coupling collision expansions. Results. Our results (energy levels, oscillator strengths, and effective collision strengths) of selected ions across the iso-electronic sequence are compared with those in archival databases and the literature. For the selected ions throughout the iso-electronic sequence, we find general agreement with the few previous R-matrix calculations of collision strengths. We illustrate the improvements for a few solar plasma diagnostics over existing CHIANTI atomic models based on distorted wave (DW) data. The electron-impact excitation data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS.

Transition Probabilities and Collision Strengths for Fine-structure Levels Excitation of Ti II

Abstract Several spectral features from the stellar and nebular objects arise due to the iron-peak Ti II fine-structure excitations. Transition probabilities and electron excitation collision strengths of iron-peak elements are important for a meaningful interpretation and analysis of the observed astrophysical spectra. Accurate description of atomic structure with open 3d-shell elements is the key to the reliable and accurate computation of radiative and collision rates. The term-dependent one-electron orbitals in the multiconfiguration Hartree–Fock approach with adjustable configuration expansions and semi-empirical fine-tuning for energy corrections have been used in achieving highly accurate target description. A total of 314 Ti II fine-structure levels of the ground 3d 24s and excited 3d 3, 3d4s 2, 3d 24p, 3d 25s, 3d4s4p, 3d 24d, 3d 25p, and 3d 24f configurations have been included in the calculations of these atomic parameters. The present calculation of collision strengths has been performed in a close-coupling approximation based on the B-spline Breit–Pauli R-matrix method with inclusion of spin–orbit interaction term in the Hamiltonian matrices. Effective collision strengths over a Maxwellian distribution of electron velocities at temperatures in the range from 103 to 105 K have been reported for transitions between the 314 fine-structure levels. These wide array of transitions give rise to many main Ti II infrared, optical, and ultraviolet lines from a variety of astrophysical objects. Our calculated parameters are compared with the available other theoretical and experimental results, and through this comparison likely uncertainties in our results have been estimated, especially for transitions among the low-lying fine-structure levels of astrophysical importance.

Collision Strengths and Effective Collision Strengths for Allowed Transitions among the n ≤ 5 Degenerate Levels of Atomic Hydrogen

We report calculations of collision strengths and effective collision strengths for 26 allowed transitions among the n≤ 5 degenerate levels of atomic hydrogen for which the close-coupling (CC) and Born approximations have been used. Results are listed over a wide range of energies (up to 100 Ryd) and temperatures (up to 107 K), sufficient for applications over a variety of plasmas, including fusion. Similar results have also been calculated for deuterium, but they negligibly differ with those of hydrogen.

Identification of Near-infrared [Se iii] and [Kr vi] Emission Lines in Planetary Nebulae∗

Abstract We identify [Se iii] 1.0994 μm in the planetary nebula (PN) NGC 5315 and [Kr vi] 1.2330 μm in three PNe from spectra obtained with the Folded-Port InfraRed Echellette (FIRE) spectrometer on the 6.5 m Baade Telescope. Se and Kr are the two most widely detected neutron-capture elements in astrophysical nebulae, and can be enriched by s-process nucleosynthesis in PN progenitor stars. The detection of [Se iii] 1.0994 μm is particularly valuable when paired with observations of [Se iv] 2.2864 μm, as it can be used to improve the accuracy of nebular Se abundance determinations, and allows Se ionization correction factor (ICF) schemes to be empirically tested for the first time. We present new effective collision strength calculations for Se2+ and Kr5+, which we use to compute ionic abundances. In NGC 5315, we find that the Se abundance computed from Se3+/H+ is lower than that determined with ICFs that incorporate Se2+/H+. We compute new Kr ICFs that take Kr5+/H+ into account, by fitting correlations found in grids of Cloudy models between Kr ionic fractions and those of more abundant elements, and use these to derive Kr abundances in four PNe. Observations of [Se iii] and [Kr vi] in a larger sample of PNe, with a range of excitation levels, are needed to rigorously test the ICF prescriptions for Se and our new Kr ICFs.

Optimisation and assessment of theoretical impurity line power coefficients relevant to ITER and DEMO

Total radiated line power coefficients for ions of medium to heavy weight elements, called coefficients in the atomic data and analysis structure, have been improved by algorithmically optimising the selection of configuration sets that underpin the calculation to include the most important radiating transitions driven by both the ground and metastable configurations and to establish and limit the error of truncation. The optimised calculations typically differ from Pütterich by 20%–30% with truncation error . Further appraisal of error due to atomic level bundling, atomic structure and collision strength calculation methods has been carried out. It is shown that bundling to configurations is accurate to for all ions except those with closed-shell ground configurations which give errors up to a factor 2–3. For near neutral, closed-shell ions, plane-wave Born collision strength calculations, which omit spin-change, give substantial error in comparison with distorted-wave calculations of . For highly charged ions, spin-system breakdown reduces the error in the markedly, typically . The error introduced by the atomic structure codes used here, autostructure and the Cowan code, is probably limited to .

Collision strengths and transition probabilities for Co ii infrared forbidden lines

We calculate collision strengths and their thermally-averaged Maxwellian values for electron excitation and de-excitation between the fifteen lowest levels of singly-ionised cobalt, Co+, which give rise to emission lines in the near- and mid-infrared. Transition probabilities are also calculated and relative line intensities predicted for conditions typical of supernova ejecta. The diagnostic potential of the 10.52, 15.46 and 14.74 micro-metre transition lines is briefly discussed.

THERMALLY AVERAGED COLLISION STRENGTHS FOR EXTREME-ULTRAVIOLET LINE OF Fe ix

Collision strengths and thermally averaged collision strengths for a large number of extreme-ultraviolet lines of Fe ix arising by electron impact have been reported. The thermally averaged collision strengths are calculated at electron temperatures in the range 104–107 K for the 122,043 forbidden and allowed transitions between the 370 fine-structure levels. The atomic parameters for Fe ix play an important role in modeling of various astrophysical plasmas, including especially the solar corona. The B-spline Breit–Pauli R-matrix method has been used in the calculation of collision strengths. The target wave functions and transition probabilities have been determined by combining the multiconfiguration Hartree–Fock method with the B-spline box-based multichannel expansions. We have included 370 fine-structure levels of Fe ix in the energy region up to states. The close-coupling expansion includes levels of the , configurations and some low-lying levels of the configuration in our collision strengths and transition probabilities calculations. There is a good agreement with the previous R-matrix collision strength calculations by Storey et al. and Del Zanna et al. for transitions between the lowest 17 levels of the , and configurations, especially for electron temperatures log T(K) ≥ 5.0. The transitions between the first 17 levels are dominated by Rydberg series of resonances converging to the levels of the configuration. The present results and the calculation of Del Zanna et al. show significant differences for many weaker forbidden and intercombination transitions with thermally averaged collision strengths smaller than 0.01.

EFFECTIVE COLLISION STRENGTHS FOR FINE-STRUCTURE TRANSITIONS IN Si VII

The effective collision strengths for electron-impact excitation of fine-structure transitions in Si vii are calculated as a function of electron temperature in the range 5000–2,000,000 K. The B-spline Breit–Pauli R-matrix method has been used to calculate collision strengths by electron impact. The target wave functions have been obtained using the multi-configuration Hartree–Fock method with term-dependent non-orthogonal orbitals. The 92 fine-structure levels belonging to the 46 LS states of 2s22p4, 2s2p5, 2p6, 2s22p33s, 2s22p33p, 2s22p33d, and 2s2p43s configurations are included in our calculations of oscillator strengths and collision strengths. There are 4186 possible fine-structure allowed and forbidden transitions among the 92 levels. The present excitation energies, oscillator strengths, and collision strengths have been compared with previous theoretical results and available experimental data. Generally, a good agreement is found with the 6 LS-state close-coupling approximation results of Butler & Zeippen and the 44 LS-state distorted wave calculation of Bhatia & Landi.

Excitation cross-sections by electron impact for O V and O VI levels

Radiative atomic and electron impact excitation data for O V and O VI ions have been calculated. The radiative atomic data have been calculated with the AUTOSTRUCTURE code. Besides the onebody and the two-body fine structure interactions, the two-body non-fine structure operators of the Breit–Pauli Hamiltonian, namely contact spin–spin, two-body Darwin and orbit–orbit are incorporated in AUTOSTRUCTURE. The scattering problem has been treated in the Breit–Pauli distorted wave approximation using the same code AUTOSTRUCTURE .T he OV atomic calculations have been extended from 46 to 92 levels. We have calculated excitation cross-sections for the O V 2s 2 −2s2p and the O VI 2s−2p transitions at energies near the corresponding excitation threshold regions. We have also calculated collision strengths for transitions from the most important levels for collisional excitation at electron energies up to 120 Ry for O V and up to 140 Ry for O VI. Our results have been compared with the available theoretical/experimental ones and a satisfactory agreement has been found between them.

Dirac R-matrix calculation for electron-impact excitation of S xiii

Context. Sulfur emission lines in the soft X-ray and extreme-ultraviolet regions are observed in a variety of laboratory and astrophys- ical spectra. But accurate electron impact excitation data for S xiii for state-of-the-art NLTE spectral models are scarce. Aims. We calculated electron-impact excitation collision strengths and effective collision strengths of S xiii for transitions among the lowest-lying 98 fine-structure states 1s 2 2lnlcorresponding to principal quantum numbers n = 2,3,4. The effective collision strengths for these transitions were computed over a wide temperature range (log10 Te (K) = 4.53-7.53) for various astrophysical plasma conditions. Methods. We used the fully-relativistic parallel Dirac R-matrix code to calculate collision strengths. To generate target wavefunctions and energy levels for scattering calculations, we employed the GRASP0 multi-configuration Dirac-Fock code for states up to n = 5. Results. The wavefunctions are generated from 27 configurations - 1s 2 2lnl � (n = 2,3,4,5) - giving rise to 166 jjenergy levels. The collision and effective collision strengths among the lowest 98 fine-structure levels are compared with the previous theoretical calculations. The collision strengths for most transitions agree well at higher incident electron energies. Conclusions. The resonant contributions to effective collision strengths are most dominant at lower temperatures.

Analogues of relativistic integrals: their application in R-matrix method for highly charged tungsten ions

The electron-impact collision strength calculations using different R-matrix code versions are performed for the 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4l (l = 0, 1, 2, 3) configuration levels of the W 45+ ion. The influence of relativistic effects on the bound-bound, bound-continuum, and continuum-continuum integrals of the collision strength is studied in quasirelativistic and relativistic approximations. A suitability of our introduced relativistic integrals method for highly charged ions is cross-checked by comparing results of different relativistic calculation methods.

Analogues of relativistic integrals: their application in R-matrix method for highly charged tungsten ions

The electron-impact collision strength calculations using different R-matrix code versions are performed for the 1s22s22p63s23p63d104l (l = 0, 1, 2, 3) configuration levels of the W45+ ion. The influence of relativistic effects on the bound-bound, bound-continuum, and continuum-continuum integrals of the collision strength is studied in quasirelativistic and relativistic approximations. A suitability of our introduced relativistic integrals method for highly charged ions is cross-checked by comparing results of different relativistic calculation methods.

COLLISION STRENGTHS AND EFFECTIVE COLLISION STRENGTHS FOR TRANSITIONS WITHIN THE GROUND-STATE CONFIGURATION OF S III

We have carried out a 29-state R-matrix calculation in order to calculate collision strengths and effective collision strengths for the electron impact excitation of S III. The recently developed parallel RMATRX II suite of codes have been used, which perform the calculation in intermediate coupling. Collision strengths have been generated over an electron energy range of 0-12 Ryd, and effective collision strength data have been calculated from these at electron temperatures in the range 1000-100,000 K. Results are here presented for the fine-structure transitions between the ground-state configurations of 3s 23p 2 3 P 0, 1, 2, 1 D 2, and 1 S 0, and the values given resolve a discrepancy between two previous R-matrix calculations.

Effective collision strengths for transitions in Ni XIX

Aims. In this paper we report electron impact collision strengths and excitation rates for transitions among the lowest 89 levels of Ni xix. Methods. The Dirac atomic R -matrix code (darc) is adopted for the calculations of collision strengths and subsequently the effective collision strengths. Results. Collision strengths for resonance transitions among 89 levels arising from the (1s 2 ) 2s 2 2p 6 , 2s 2 2p 5 3$\ell$, 2s2p 6 3$\ell$, 2s 2 2p 5 4$\ell$, and 2s2p 6 4$\ell$ configurations of Ni xix are reported over a wide energy range below 250 Ryd. Additionally, effective collision strengths for all 3916 transitions among the 89 levels are listed over a wide temperature range below 10 7 K. Comparisons are made among different calculations and the accuracy of the data is assessed. Finally, comparisons between theoretical and experimental intensity ratios of some prominent lines of Ni xix are discussed.

Effective collision strengths for allowed transitions among the n $\mathsf{\le}$ 5 degenerate levels of Al XIII

Aims. In this paper we report on calculations of collision strengths and effective collision strengths for allowed transitions among the $n \le$ 5 degenerate levels of Al xiii. Methods. The Dirac atomic R -matrix code (darc) has been adopted for these calculations. Results. Collision strengths are reported over a wide energy range below 300 Ryd, and effective collision strengths are provided for electron temperatures of 4.4 ≤ log $T_{\rm e} \le$ 6.8 K.

The agreement of Breit–Pauli and Dirac R-matrix collision strengths for iron peak elements: an Fe14+ case study

In calculating collision strengths and excitation rates for electron impact on moderately ionized iron peak elements, one might question whether the Breit–Pauli R-matrix method is sufficiently accurate as compared with the Dirac R-matrix method. We test this for Fe14+ by removing as far as possible any variation in algorithmic features, such as the energy mesh and target state expansion, as opposed to genuine differences between the two approaches. We find the average difference between the Breit–Pauli and Dirac R-matrix effective collision strengths is only 6%, which confirms the hypothesis that if one gets the Dirac and Breit–Pauli target states close, and resolves the resonances adequately (we use up to 384 101 points), then the Dirac and Breit–Pauli collision strengths are in good agreement. We finally tabulate the best converged effective collision strengths for T = 105–107 K for all transitions involving the lowest 10 levels of Fe14+.

Atomic data from the IRON Project

This paper reports on the calculation of collision strengths for electron induced transitions in the beryllium-like ion Ni xxv whose ground state is 1s 2 2s 2 1 S 0 . We make use of the R-matrix method in conjunction with the intermediate frame coupling transformation (IFCT). The target has 98 fine structure states 1s 2 nl n'l' S LJ corresponding to n = 2 and n' = 2, 3, 4. Our calculation extends up to 440 Ry with respect to the ground state. In order to obtain reliable rate coefficients at high temperatures (T above 2 x 10 7 K) we have extended our collision strengths to much higher energies by using a variety of techniques, including use of Burgess's interactive code OmeUps. The effective collision strength T is tabulated against log T for the 45 transitions linking the lowest 10 levels. We also give results for 5 transitions in the X-ray region which are needed in solar studies. The temperature range 6.3 < log T < 8.3 is centred on log T = 7.1 which is where this ion has its maximum coronal abundance.