Collision Strengths For Electron Impact Excitation Research Articles

Study of electron impact excitation of H-like Si13+ ion in dense plasma environment

The relativistic configuration interaction technique has been employed to study the electron impact excitation collision strengths of H-like Si13+ ion in strongly coupled plasma environment. The analytical plasma screening b-potential has been adopted to determine the physical effects of the screened Coulomb interaction due to the influence of plasma on the atomic structure and dynamics affecting atomic processes. The modified Dirac equations are solved to obtain the bound and continuum state wave functions. We examine the plasma screening effect by considering the plasma conditions at the electron temperatures of 200, 600 and 1000 eV over electron density range of 2.0 × 1023 - 1.0 × 1024 cm−3. The present results highlight that the inclusion of plasma environment induces significant effect on the binding energies, transition energies, radiative transition probabilities, oscillator strengths and collision strengths. It has been observed that the collision strength decreases with increase in plasma electron density for a fixed temperature. Our results will be beneficial for laser produced plasmas, high energy density physics, astrophysical applications and will open the door to modelling and advanced diagnostics of solar and stellar plasmas.

Atomic Databases: Four of a Kind

In the context of atomic data computations for astrophysical applications, we review four different types of databases we have implemented for data dissemination: a database for nebular modeling; TIPTOPbase; OPserver; and AtomPy. The database for nebular plasmas is briefly discussed as a study case of a successful project. TOPbase and the OPserver were developed during the Opacity Project, an international consortium concerned with the revision of astrophysical opacities, while TIPbase was part of the Iron Project to calculate radiative transition probabilities and electron impact excitation collision strengths for iron-group ions. AtomPy is a prototype for an open, distributed data-assessment environment to engage both producers and users. We discuss design strategies and implementation issues that may help in the undertaking of present and future scientific database projects.

Energy levels, transition rates and electron impact excitation rates for B-like Kr XXXII

Energy levels and transition rates for electric-dipole, electric-quadrupole, electric-octupole, magnetic-dipole, and magnetic-quadrupole transitions among the levels arising from the n≤ 5 configurations in B-like Kr XXXII are calculated by using two state-of-the-art methods, namely, the multi-configuration Dirac–Hartree–Fock (MCDHF) approach and the second-order many-body perturbation theory (RMBPT). Our results are compared with several available experimental and other theoretical values. Electron-impact excitation (EIE) collision strengths are calculated via the independent process and isolated resonance approximation using distorted-wave (denoted by IPIRDW). Radiation damping effects on the resonance excitation contributions are included. Effective collision strengths are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Spectral line intensities are modelled by using collision radiative model, and several line pairs pointed out might be useful for density diagnostics.

Energy Levels, Transition Rates and Electron Impact Excitation Rates for the B-like Isoelectronic Sequence with Z = 24–30

Abstract We report calculations of spectroscopic accuracy for 513 states in the B-like ions with Z = 24–30. The energy levels and transition rates are calculated using the second-order many-body perturbation theory, while multiconfiguration Dirac–Hartree–Fock calculations are performed to support the former results. The present two sets of results agree excellently with each other, and can be used as benchmarks in the future. The electron-impact excitation (EIE) collision strengths are calculated based on independent processes and isolated resonances approximation using the distorted wave method. Based on the present atomic data, the spectral lines of these ions are simulated using a collisional radiative model. The amount of energy, transition data, and EIE collision strengths of high accuracy are significantly increased for several B-like ions of astrophysical interest, where experimental data are still very scarce. The results can be used in line identification, plasma modeling, and diagnostics of astrophysical plasmas.

Estimating the Level of Uncertainty in Electron-Impact Excitation and Photoionisation Rates of Low-Ionised Stages of Ni Ions

Ni iv lines can be used as diagnostics for temperature and density for various astrophysical objects. In addition, ionization of Ni2+ is one of the causes of the opacity in the interstellar medium. We calculate the photoionization of Ni2+ and the electron-impact excitation of Ni3+. We use a fully-relativistic Dirac Atomic R-Matrix Code (DARC) method. We include a large set of configurations in the expansion of the wave functions of the target, up to the n=6 atomic shell. We show preliminary results for the photoionization cross-sections of Ni2+ and the electron-impact excitation collision strengths of Ni3+. The expected final results can be implemented in the available software packages for astrophysical plasma simulation, such as CLOUDY. We also show a preliminary estimation of the error of the data by the comparison of different sets of calculations.

Electron impact excitation for He-like ions withZ= 20–42

Aims. Spectral lines of He-like ions are among the most prominent features in X-ray spectra from a large variety of astrophysical and high-temperature fusion plasmas. A reliable plasma modeling and interpretation of the spectra require a large amount of accurate atomic data related to various physical processes. In this paper, we focus on the electron-impact excitation (EIE) process. Methods. We adopted the independent process and isolated resonances approximation using distorted waves (IPIRDW). Resonant stabilizing transitions and decays to lower-lying autoionizing levels from the resonances are included as radiative damping. To verify the applicability of the IPIRDW approximation, an independent Dirac R-matrix calculation was also performed. The two sets of results show excellent agreement. Results. We report electron impact excitation collision strengths for transitions among the lowest 49 levels of the 1snl(n ≤ 5; l ≤ (n - 1)) configurations in He-like ions with 20 ≤ Z ≤ 42. The line ratios R and G are calculated for Fe XXV and Kr XXXV. Conclusions. Compared to previous theoretical calculations, our IPIRDWcalculation treats resonance excitation and radiative damping effects more comprehensively, and the resulting line emission cross sections show good agreement with the experimental observations. Our results should facilitate the modeling and diagnostics of various astrophysical and laboratory plasmas. (Less)

Scaling of collision strengths for highly-excited states of ions of the H- and He-like sequences

Emission lines from highly-excited states (n >= 5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n >= 6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, for example. We investigate the dependence on the relevant parameters: the principal quantum number n or the nuclear charge Z. We also estimate the importance of coupling to highly-excited states and the continuum by comparing the results of different sized calculations. We provide analytic formulae to calculate the electron-impact excitation collision strengths and effective collision strengths to highly-excited states (n >= 8) of H- and He-like ions. These extrapolated effective collision strengths can be used to interpret astrophysical and fusion plasma via collisional-radiative modelling.

Electron Impact Excitation of F-Like W LXVI

Electron impact excitation collision strengths are calculated for all transitions among 113 levels of the 2s 2 2p 5 , 2s2p 6 , 2s 2 2p 4 3ℓ, 2s2p 5 3ℓ, and 2p 6 3ℓ configurations of F-like W LXVI. For this purpose, Dirac Atomic R-matrix Code (DARC) has been adopted and results are listed over a wide energy range of 1000 to 6000 Ryd. For comparison purposes, analogous calculations have also been performed with the Flexible Atomic Code (FAC), and the results obtained are comparable with those from DARC.

Breit-Pauli electron-impact excitation collision strengths for transitions in O III

SynopsisCollision strengths for electron impact excitation of fine-structure transitions between the first 202 fine-structure levels of O III have been calculated using the Breit-Pauli B-spline R-matrix method. The close-coupling expansion includes levels of the 2s22p2, 2s2p3, 2s22p33l (l=0-2), 2s22p34l (l=0-2) and 2s2p23l configurations. The present results considerably improve the existing oscillator strengths and collision strengths for O III.

Advances in atomic data for plasma diagnostics

SynopsisWe present sets of new atomic data for astrophysical and fusion plasma diagnostics. We calculate electron-impact excitation collision strengths and effective collisions strengths for the Be- and Mg-like isoelectronic sequences up to Krq+. We use the R-Matrix Intermediate-Coupling Frame Transformation method. We also study the accuracy of calculations for highly-excited states and give extrapolation rules to estimate the effective collision strengths and their error at high n. We demonstrate the importance of a well converged CI/CC expansion in the R-matrix calculation to get good quality results, mainly for highly-excited states.

Collision rates for electron excitation of Mg V lines

Aims. Transition probabilities and electron impact excitation collision strengths and rates for astrophysically important lines in Mg V are reported. The 86 fine-structure levels of the 2s2p, 2s2p, 2p, 2s2p3s, 2s2p3p and 2s2p3d configurations are included in our calculations. The effective collision strengths are presented as a function of electron temperature for solar and other astrophysical applications. Methods. The collision strengths have been calculated using the B-spline Breit-Pauli R-matrix method for all fine-structure transitions among the 86 levels. The one-body mass, Darwin and spin-orbit relativistic effects are included in the Breit-Pauli Hamiltonian in the scattering calculations. The one-body and two-body relativistic operators are included in the multiconfiguration Hartree-Fock calculations of transition probabilities. Several sets of non-orthogonal spectroscopic and correlation radial orbitals are used to obtain accurate description of Mg V 86 levels and to represent the scattering functions. Results. The calculated excitation energies are in very good agreement with experiment and represents an improvement over the previous calculations. The present collision strengths show good agreement with the previously available R-matrix and distorted-wave calculations. The oscillator strengths for E1 transitions normally compare very well with previous calculations. The thermally averaged collision strengths are obtained by integrating total resonant and non-resonant collision strengths over a Maxwellian distribution of electron energies and these are presented over the temperature range log10 Te = 3.2−6.0 K.

Electron impact excitation of Si II and Fe XIV

Energy levels, radiative rates, lifetimes, collision strengths and effective collision strengths are calculated for two important Al-like ions, namely Si II and Fe XIV. For Si II, the lowest 56 levels of the 3s23p, 3s3p2 3p3 3s23d, 3s3p3d, 3s24ℓ and 3s25ℓ configurations are included, whereas for Fe XIV additional 80 levels of 3p23d, 3s3d2 and 3p3d2 are considered, but not of 3s2 5ℓ. For the determination of atomic structure GRASP has been adopted and radiative rates are calculated for all E1, E2, Ml and M2 transitions. Electron impact excitation collision strengths are calculated with the DARC code, over a wide energy range, and resonances are resolved in a fine energy mesh to determine effective collision strengths over a wide range of temperatures. Extensive comparisons are made for all atomic parameters with available theoretical and experimental data, and the accuracy of the present results is assessed. Energy levels are estimated to be accurate to ~1% and all other parameters to be better than 20%.

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 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 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$3p, 3s3p$^2$, 3s$^2$3d, 3p$^3$, 3s3p3d, 3p$^2$3d, 3s3d$^2$, 3p3d$^2$ and 3s$^24\ell$ 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, as well 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.

Energy levels, radiative rates and electron impact excitation rates for transitions in Si ii

Energies for the lowest 56 levels, belonging to the 3s$^2$3p, 3s3p$^2$, 3p$^3$, 3s$^2$3d, 3s3p3d, 3s$^2$4$\ell$ and 3s$^2$5$\ell$ configurations of Si II, are calculated using the {\sc grasp} (General-purpose Relativistic Atomic Structure Package) code. Analogous calculations have also been performed (for up to 175 levels) using the Flexible Atomic Code ({\sc fac}). Furthermore, radiative rates are calculated for all E1, E2, M1 and M2 transitions. Extensive comparisons are made with available theoretical and experimental energy levels, and the accuracy of the present results is assessed to be better than 0.1 Ryd. Similarly, the accuracy for radiative rates (and subsequently lifetimes) is estimated to be better than 20% for most of the (strong) transitions. Electron impact excitation collision strengths are also calculated, with the Dirac Atomic R-matrix Code ({\sc darc}), over a wide energy range up to 13 Ryd. Finally, to determine effective collision strengths, resonances are resolved in a fine energy mesh in the thresholds region. These collision strengths are averaged over a Maxwellian velocity distribution and results listed over a wide range of temperatures, up to 10$^{5.5}$ K. Our data are compared with earlier $R$-matrix calculations and differences noted, up to a factor of two, for several transitions. Although scope remains for improvement, the accuracy for our results of collision strengths and effective collision strengths is assessed to be about 20% for a majority of transitions.

ELECTRON IMPACT EXCITATION COLLISION STRENGTHS FOR EXTREME ULTRAVIOLET LINES OF Fe VII

Extensive calculations have been performed for electron impact excitation collision strengths and oscillator strengths for the Fe VII extreme ultraviolet lines of astrophysical importance. The collision strengths for fine-structure transitions are calculated in the B-spline Breit-Pauli R-matrix approach. The target wavefunctions have been calculated in the multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals. The close-coupling expansion includes 189 fine-structure levels of Fe VII belonging to terms of the ground 3p 63d 2 and excited 3p 53d 3, 3p 63d4l, 3p 63d5s, and 3p 63d5p configurations. The effective collision strengths are determined from the electron excitation collision strengths by integration over a Maxwellian distribution of electron velocities. The effective collision strengths are provided for 17766 fine-structure transitions at electron temperatures from 104 to 107 K. Our results normally agree with the previous R-matrix frame-transformation calculations by Witthoeft & Badnell. However, there are important differences for some transitions with the previous calculations. The corrections to the previous results are mainly due to more extensive expansions for the Fe VII target states.

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.

Methods, algorithms, and computer codes for calculation of electron-impact excitation parameters

We describe the computer codes, developed at Vilnius University, for the calculation of electron-impact excitation cross sections, collision strengths, and excitation rates in the plane-wave Born approximation. These codes utilize the multireference atomic wavefunctions which are also adopted to calculate radiative transition parameters of complex many-electron ions. This leads to consistent data sets suitable in plasma modelling codes. Two versions of electron scattering codes are considered in the present work, both of them employing configuration interaction method for inclusion of correlation effects and Breit-Pauli approximation to account for relativistic effects. These versions difer only by one-electron radial orbitals, where the first one employs the nonrelativistic numerical radial orbitals, while the other version uses the quasirelativistic radial orbitals. The accuracy of produced results is assessed by comparing radiative transition and electron-impact excitation data for neutral hydrogen, helium, and lithium atoms as well as highly charged tungsten ions with theoretical and experimental data available from other sources.

Methods, algorithms, and computer codes for calculation of electron-impact excitation parameters

We describe the computer codes, developed at Vilnius University, for the calculation of electron-impact excitation cross sections, collision strengths, and excitation rates in the plane-wave Born approximation. These codes utilize the multireference atomic wavefunctions which are also adopted to calculate radiative transition parameters of complex many-electron ions. This leads to consistent data sets suitable in plasma modelling codes. Two versions of electron scattering codes are considered in the present work, both of them employing configuration interaction method for inclusion of correlation effects and Breit-Pauli approximation to account for relativistic effects. These versions differ only by one-electron radial orbitals, where the first one employs the non-relativistic numerical radial orbitals, while another version uses the quasirelativistic radial orbitals. The accuracy of produced results is assessed by comparing radiative transition and electron-impact excitation data for neutral hydrogen, helium and lithium atoms as well as highly-charged tungsten ions with theoretical and experimental data available from other sources.

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.