Effective Collision Strengths For Transitions Research Articles

Radiative Rates and Electron Impact Excitation Rates for Transitions in He II

We report calculations of energy levels, radiative rates, collision strengths and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of He II. The general-purpose relativistic atomic structure package (grasp) and Dirac atomic R-matrix code (darc) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 9 Ryd (10 5.4 K). Comparisons are made with earlier available results, and the accuracy of the data is assessed.

Radiative rates and electron-impact excitation for then≤ 6 fine-structure levels in H-like ions with 13 ≤Z≤ 42

Context. Many observed emission lines from space missions are due to highly charged H-like ions. An analysis of the lines provides information on the temperature, density, and chemical composition of plasmas. A wide range of atomic parameters, such as energy levels, radiative rates, and excitation rate coefficients are needed to achieve this goal.Aims. In this paper we report on calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the 36 lowest levels of the n ≤ 6 configurations of highly charged H-like ions with 13 ≤ Z ≤ 42.Methods. The widely used Flexible Atomic Code (FAC) is adopted for the calculation. Energy levels and radiative rates are calculated within the relativistic configuration-interaction method. Employing relativistic distorted-wave approximation, direct excitation collision strengths are calculated at eleven scattered electron energies E ′ f = 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.5, where E ′ f is in units of Z 2 rydbergs. Collision strengths at higher energies are estimated by interpolation/extrapolation using relativistic Bethe form. Resonance contributions through the relevant He-like doubly excited n ′l ′n ′′l ′′ configurations with n ′ ≤ 7 and n ′′ ≤ 75 are explicitly taken into account using the independent-process isolated-resonance approximation. Radiation damping effects are taken into account.Results. We present the radiative rates, oscillator strengths, and line strengths for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), magnetic quadrupole (M2), electric octupole (E3), and magnetic octupole (M3) transitions. Assuming a Maxwellian electron velocity distribution, we report effective collision strengths over a wide temperature range between 2 × 103 × Z 2 and 2 × 106 × Z 2 K. We believe that the present results are the most extensive and definitive atomic dataset to date for highly charged H-like ions.

Electron Impact Excitation of N-like Ca XIV

Abstract We present a close-coupling R-matrix calculation of the electron impact excitation of N-like Ca XIV. GRASP (general-purpose relativistic atomic structure package) was used to obtain the target states. Level energies are reported for the 272 levels of the target ion. The oscillator strengths and radiative rates were calculated for E1, E2, M1, and M2 transitions among these levels. In order to determine the collision strength, the lowest 84 levels were used as the target model, together with 40 partial waves included in the R-matrix calculation. The effective collision strengths were obtained by integrating the collision strengths over a Maxwellian electron energies distribution. Comparisons were made with our FAC and the LB results by Landi and Bhatia (2005, At. Data Nucl. Data Tables, 90, 177). Good agreements are shown for level energies, oscillator strengths and radiative rates, respectively. As to the collision strength, a mass of resonances appears in the R-matrix results, which are important in the determination of effective collision strengths. The discrepancies of the effective collision strengths between results from the R-matrix and from FAC are discussed. Finally, the effective collision strengths for transitions among the first 84 levels are reported. To test our results, we also compared the predicted line ratio with the observed values.

Dirac R-matrix collision strengths and effective collision strengths for transitions of Ni xvii

Context. Electron impact excitation collision strengths are required for the analysis and interpretation of stellar observations. Aims. This calculation aims to provide fine structure effective collision strengths for the Nixvii ion using a method which includes contributions from resonances. Methods. A fully relativistic R-matrix calculation has been performed using the DARC code. In the structure part of our calculation 141 fine-structure levels are employed and 37 of these are used in the scattering calculation. Results. Collision strengths have been determined for 666 fine-structure transitions arising from the 37 lowest j-levels involving configurations 3s 2 ,3 p 2 ,3 d 2 , 3s3p, 3s3d, 3p3d and 3s4s. The effective collision strengths for these transitions have been calculated for electron temperatures (Te) in the range log 10 Te(K) = 4.5−8.0. Effective collision strengths are tabulated for transitions between the first ten fine structure levels, arising from the 3s 2 , 3s3p and 3p 2 configurations. The remaining transitions are available at the CDS as

Radiative rates and electron impact excitation rate coefficients for Ne-like selenium, Se XXV

In this article we report calculations of energy levels, radiative rates, electron impact collision strengths, and effective collision strengths for transitions among the 241 fine-structure levels arising from 2 l 8 and 2 l 7 n ′ l ′ ( n ′ ≤ 6 and l ′ ≤ n ′ − 1 ) configurations of Ne-like Se XXV using the Flexible Atomic Code. Energy levels and radiative rates are calculated within the relativistic configuration-interaction method. Direct excitation collision strengths are calculated using the relativistic distorted-wave approximation and high-energy collision strengths are obtained in the relativistic plane-wave approximation. Resonance contributions through the relevant Na-like doubly-excited configurations 2 l 7 n ′ l ′ n ″ l ″ ( 3 ≤ n ′ ≤ 7 , l ′ ≤ n ′ − 1 , n ′ ≤ n ″ ≤ 50 , and l ″ ≤ 8 ) are explicitly taken into account via the independent-process and isolated-resonance approximation using distorted waves. Resonant stabilizing transitions and possibly important radiative decays from the resonances toward low-lying autoionizing levels are considered. In addition, the resonance contributions from Na-like 2 l 6 3 l ′ 3 l ″ n ‴ l ‴ ( n ‴ = 3 − 6 ) configurations are included and found to be predominant for many transitions among the singly-excited states in Ne-like Se XXV. We present the radiative rates, oscillator strengths, and line strengths for all electric dipole, magnetic dipole, electric quadrupole, magnetic quadrupole, electric octopole, and magnetic octopole transitions among the 241 levels. The effective collision strengths are reported for all 28920 transitions among the 241 levels over a wide temperature range up to 10 keV. To assess the reliability and accuracy of the present collisional data, we have performed a 27-state close-coupling calculation, employing the Dirac R-matrix theory. The results from the close-coupling calculation and the independent-process calculation for the identical target states are found to be in good agreement.

Radiative rates and electron impact excitation rate coefficients for H-like Fe XXVI

Abstract In this paper we report on calculations on energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 36 levels of the n ≤ 6 configurations of H-like Fe XXVI. Flexible atomic code (FAC) is adopted for the calculation. Energy levels and radiative rates are calculated within relativistic configuration-interaction method. Direct excitation collision strength is calculated using relativistic distorted-wave approximation. Resonance contributions through the relevant He-like doubly excited n ′ l ′ n ″ l ″ configurations with n ′ ≤ 7 and n ″ ≤ 75 are explicitly taken into account using the isolated process and isolated resonances approximation. We present the radiative rates, oscillator strengths, and line strengths for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among the 36 levels. Furthermore, collision strengths and effective collision strengths are reported for all the 630 transitions among the above 36 levels over a wide energy (temperature) range up to 25 keV ( 10 9 K ) . Extensive comparisons are made with earlier available results and the accuracy of the data is assessed.

Radiative rates and electron impact excitation rates for transitions in Cr VIII

Aims. In this paper we report on calculations of energy levels, radiative rates, oscillator strengths, line strengths, and effective collision strengths for transitions among the lowest 362 levels of the (1s 2 2s 2 2p 6 )3 s 2 3p 5 ,3 s3p 6 ,3 s 2 3p 4 3d, 3s3p 5 3d, 3s 2 3p 3 3d 2 ,3 s3p 4 3d 2 ,3 p 6 3d, and 3s 2 3p 4 4� configurations of Cr viii. Methods. The general-purpose relativistic atomic structure package (grasp) and flexible atomic code (fac) are adopted for the calculations. Results. Radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among the 362 levels. Comparisons are made with earlier available results and the accuracy of the data is assessed. Additionally, lifetimes for all 362 levels are listed, although comparisons with other theoretical results are limited to only a few levels. Our energy levels are estimated to be accurate to better than 3% (within 0.4 Ryd), whereas results for other parameters are probably accurate to better than 20%. Finally, electron impact collision strengths and excitation rates are computed for all transitions over a wide energy (temperature) range. For these calculations, FAC is adopted and results in the form of effective collision strengths are reported over a wide temperature range of 10 5.0 −10 6.6 K.

Effective collision strengths for transitions of Ni XVII

Electron impact excitation collision strengths are required for the analysis and interpretation of stellar observations. This calculation aims to provide fine structure effective collision strengths for the Nixvii ion using a method which includes contributions from resonances. A DARC calculation has been performed, involving 37 Jπ states. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. The non-zero effective collision strengths for transitions between the fine structure levels are given for electron temperatures (Te) in the range log10Te(K) = 4.5 - 8.5. Data for several transitions from the ground state are discussed in this paper.

Energy levels, oscillator strengths, and effective collision strengths for transitions in Fe XIV

In this paper we report atomic data, namely energy levels, radiative rates, lifetimes, collision strengths, and excitation rate coefficients, for transitions among 162 levels of the (1s22s22p6) 3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2, 3p3d2, 3d3, 3s3p4s, and 3s24ℓ configurations of Fe XIV. For the calculations of energy levels and radiative rates both the grasp and fac codes have been adopted, whereas for the collision strengths only fac is employed.

Excitation rates for transitions in Kr XXXII

In this paper we report our results for collision strengths and effective collision strengths for transitions among the lowest 125 levels of the 2s22p, 2s2p2, 2p3, 2s23ℓ, 2s2p3ℓ, and 2p23ℓ configurations of Kr XXXII. For our calculations both the FAC and DARC codes have been employed.

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.

Breit-PauliR-matrix calculation of fine-structure effective collision strengths for the electron impact excitation of Mg V

Context. Electron impact excitation collision strengths are required for analysing and interpreting stellar observations. Aims. This calculation aims to provide fine-structure effective collision strengths for the Mg ix ion using a method that includes contributions from resonances. Methods. A 26-state Breit-Pauli R-matrix calculation has been performed. The target states are represented by configuration interaction wavefunctions and consist of the 26 lowest LS states, having configurations 2s 2 , 2s2p, 2p 2 , 2s3s, 2s3p, 2s3d, 2p3s, 2p3p, and 2p3d. These target states give rise to 46 fine structure levels and 1035 possible transitions. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. Results. The non-zero effective collision strengths for transitions between the fine structure levels are given for electron temperatures (Te) in the range log10 Te(K) = 3.0–7.0. Values for selected transitions are given in this paper and links provided to the entire data set.

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.

Radiative rates and electron impact excitation rates for H-like Ar XVIII

Aims. In this paper we report on calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of H-like Ar xviii.

Radiative rates and electron impact excitation rates for H-like Fe XXVI

Aims. In this paper we report on calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of H-like Fe XXVI. Methods. The general-purpose relativistic atomic structure package (GRASP) and Dirac atomic R -matrix code (DARC) are adopted for the calculations. Results. Radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective collision strengths are reported for all the 300 transitions among the above 25 levels over a wide energy (temperature) range up to 1500 Ryd (10 7.7 K). Comparisons are made with earlier available results and the accuracy of the data is assessed.

“Electron collisional excitation of argon-like Ni XI using the Breit-Pauli R-matrix method”

In a recent paper, Verma et al. [Eur. Phys. J. D 42, 235 (2007)] have reported results for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 17 levels of the (1s22s22p6)3s23p6, 3s23p53d and 3s3p63d configurations of Ni xi. They adopted the civ3 and R-matrix codes for the generation of wavefunctions and the scattering process, respectively. In this paper, through two independent calculations performed with the fully relativistic darc (along with grasp) and fac codes, we demonstrate that their results are unreliable. New data are presented and their accuracy is assessed.

Electron impact excitation of Fe XVI: radiative and excitation rates

Aims. In this paper we report calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions in Fe XVI. Methods. For energy levels and radiative rates we have used the General purpose Relativistic Atomic Structure Package (GRASP), and for the compuations of collision strengths the Dirac Atomic R-matrix Code (DARC) has been adopted. Results. Energies for the lowest 39 levels among the n < 7 (l ≤ 4) configurations of Fe XVI are reported. Additionally, radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (El), magnetic dipole (Ml), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Electron impact excitation collision strengths have also been calculated for all 741 transitions among the above 39 levels over a wide energy range up to 220 Ryd. Resonances have been resolved in the threshold region, and effective collision strengths have been obtained over a wide temperature range up to 10 7 K. Comparisons are made with the available results in the literature, and the accuracy of the present results is assessed.

Effective collision strengths for transitions in Fe X

Collision strengths for 4005 transitions among the lowest 90 levels of the (1s22s22p6) 3s23p5, 3s3p6, 3s23p43d, 3s3p53d and 3s23p33d2 configurations of Fe X have been calculated using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2005, Comput. Phys. Commun., in preparation), over a wide energy range up to 210 Ryd. Resonances have been resolved in the threshold region, and effective collision strengths have been obtained over a wide temperature range up to 107 K. The present calculations should represent a significant improvement (in both range and accuracy) over the earlier available results of Bhatia & Doschek (1995, At. Data Nucl. Data Tables, 60, 97), Tayal (2001, ApJS, 132, 117) and Pelan & Berrington (2001, A&A, 365, 258). Based on several comparisons, the accuracy of our data is assessed to be better than 20%, for a majority of transitions.

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.

Radiative Rates, Collision Strengths and Effective Collision Strengths for Transitions in Gd XXXVII

Energy levels and radiative rates for transitions among 107 fine-structure levels belonging to the (1s22s22p6) 3s23p63d10, 3s23p63d94l, 3s23p53d104l, and 3s3p63d104l configurations of Ni-like Gd XXXVII have been calculated using the fully relativistic GRASP code. Radiative rates and oscillator strengths are tabulated for all allowed transitions among these levels. Additionally, collision strengths for transitions among the lowest 59 levels have been computed using the Dirac Atomic R-matrix Code. Resonances in the threshold region have been delineated, but results for collision strengths are tabulated only at energies above thresholds in the range 120 ≤ E ≤ 800 Ry. Effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron velocities, have also been calculated and are tabulated over a wide electron temperature range of 105.0 to 107.7 K. Our energy levels are assessed to be accurate to within 1%, while oscillator strengths, collision strengths, and effective collision strengths for all strong transitions are probably accurate to better than 20%.