Margaret Scott

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 0-12xa0Ryd, and effective collision strength data have been calculated from these at electron temperatures in the range 1000-100,000xa0K. 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.

Electron impact excitation of Fe II : Total LS effective collision strengths

We present total effective collision strengths for electron-impact excitation of Fe II, calculated using the parallel R-matrix program PRMAT, for all sextet to quartet forbidden transitions among the lowest 113 LS states formed from the 3d64s, 3d7, 3d54s2, 3d64p and 3d54s4p basis configurations. After a detailed and systematic study of configuration-interaction effects in both the target and the collision wavefunctions, it was found that an additional 21 configurations needed to be included in the CI expansion to obtain significantly more accurate target state and collision wavefunctions. A total of 1785 individual lines are considered over a wide range of electron temperatures, 30–100 000 K, of particular importance in astrophysical applications. A detailed comparison is made with a previous 3 configuration approximation and significant differences of up to a factor of 2 are reported at the lowest temperatures considered. The inclusion of the additional 3d54s2 and 3d54s4p levels in the present work together with the additional CI effects are found to cause significant changes to the total effective collision strengths for the low-lying transitions from the ground state, particularly at very low temperatures. The disparities are found to be considerably less at the higher temperatures considered.

Electron-impact excitation of Fe II. Collision strengths and effective collision strengths for low-lying fine-structure forbidden transitions.

Context. Considerable demand exists for electron excitation data for Ni ii, since lines from this abundant ion are observed in a wide variety of laboratory and astrophysical spectra. The accurate theoretical determination of these data can present a significant challenge however, due to complications arising from the presence of an open 3d-shell in the description of the target ion. Aims. In this work we present collision strengths and Maxwellian averaged effective collision strengths for the electron-impact excitation of Ni ii. Attention is concentrated on the 153 forbidden fine-structure transitions between the energetically lowest 18 levels of Ni ii .E ffective collision strengths have been evaluated at 27 individual electron temperatures ranging from 30–100 000 K. To our knowledge this is the most extensive theoretical collisional study carried out on this ion to date. Methods. The parallel R-matrix package RMATRX II has recently been extended to allow for the inclusion of relativistic effects. This suite of codes has been utilised in the present work in conjunction with PSTGF to evaluate collision strengths and effective collision strengths for all of the low-lying forbidden fine-structure transitions. The following basis configurations were included in the target model – 3d 9 ,3 d 8 4s, 3d 8 4p, 3d 7 4s 2 and 3d 7 4s4p – giving rise to a sophisticated 295 jj-level, 1930 coupled channel scattering problem. Results. Comprehensive comparisons are made between the present collisional data and those obtained from earlier theoretical evaluations. While the effective collision strengths agree well for some transitions, significant discrepancies exist for others.

Configuration Interaction Effects in low-energy electron collisions with Fe II

Partial wave collision strengths are presented for low-energy electron-impact transitions in Fe II between the 3d 6 4 sa 6 D e ground state and the 3d 7 a 4 F e , 3d 6 4s a 4 D e and 3d 7 a 4 P e low-lying excited states. The collision strengths are calculated in LS coupling using a new Fortran 95 R-matrix program including all terms of the 3d 6 4s, 3d 7 , 3d 6 4p, 3d 5 4s 2 and 3d 5 4s4p configurations in the close coupling expansion of the collision wavefunction. Special emphasis is given to the inclusion of configuration interaction (CI) effects both in the target and in the collision wavefunctions. In both cases series of calculations are carried out where additional CI terms are included systematically. It is found that in order to obtain close to converged low-energy partial wave collision strengths two-electron excitations from the 3p shell to the 3d shell as well as pseudo s and d orbitals must be included in the CI expansions. Also resonance effects in low-energy partial wave collision strengths are found to depend sensitively on the representation of the d orbitals in the CI expansion of the collision wavefunction. Finally, CI models for both the target and collision wavefunctions are defined which can be used in proposed calculations to obtain accurate total collision strengths and effective collision strengths for transitions between LS-coupled terms and between fine-structure levels of Fe II.

Breit-Pauli R-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.

Electron-impact excitation of Fe II

We report in this paper the computation of accurate total collision strengths and effective collision strengths for electron-impact excitation of FeII, using the parallel R-matrix program PRMAT. Target states corresponding to the 3d64s, 3d7, 3d64p and 3d54s4s basis configurations were included in the calculations giving rise to a 113 LS state 354 coupled channel problem. Following a detailed systematic study of correlation effects in both the target state and collision wavefunctions, it was found that an additional 21 configuration functions needed to be included in the Configuration Interaction expansion to obtain significantly more accurate target states and collision wavefunctions. This much improved 26-configuration model has been used to calculate converged total effective collision strengths for all sextet to quartet transitions among these levels with total spin S = 2, giving a total of 1785 lines. These calculations have laid the foundation for an approach which may be adopted in the study of electron collisions with the low ionization stages of other iron peak elements. The work has been further extended with the commencement of a Breit-Pauli relativistic calculation for one of the smaller models and includes 262 fine-structure levels and over 1800 coupled channels. At the same time the PRMAT parallel R-matrix package is being extended to include relativistic effects which will allow us to attempt the more sophisticated 26-configuration model and produce for the first time the amount and quality of atomic data required to perform a meaningful synthesis of the Fe II spectrum.

Electron-impact Excitation of Ni II: Effective Collision Strengths for Optically Allowed Fine-structure Transitions

In this paper, we present collision strengths and Maxwellian averaged effective collision strengths for the electron-impact excitation of Ni II. Attention is expressly concentrated on the optically allowed fine-structure transitions between the 3d 9, 3d 84s, and 3d 74s 2 even parity levels and the 3d 84p and 3d 74s 4p odd parity levels. The parallel RMATRXII R-matrix package has been recently extended to allow for the inclusion of relativistic fine-structure effects. This suite of codes has been utilized in conjunction with the parallel PSTGF and PSTGICF programs in order to compute converged total collision strengths for the allowed transitions with which this study is concerned. All 113 LS terms identified with the 3d 9, 3d 84s, 3d 74s 2, 3d 84p, and 3d 74s 4p basis configurations were included in the target wavefunction representation, giving rise to a sophisticated 295 jj-level, 1930 coupled channel scattering complex. Maxwellian averaged effective collision strengths have been computed at 30 individual electron temperatures ranging from 30 to 1,000,000 K. This range comfortably encompasses all temperatures significant to astrophysical and plasma applications. The convergence of the collision strengths is exhaustively investigated and comparisons are made with previous theoretical works, where significant discrepancies exist for the majority of transitions. We conclude that intrinsic in achieving converged collision strengths and thus effective collision strengths for the allowed transitions is the combined inclusion of contributions from the (N + 1) partial waves extending to a total angular momentum value of L = 50 and further contributions from even higher partial waves accomplished by employing a top-up procedure.

Electron-impact Excitation of Cr?II: A Theoretical Calculation of Effective Collision Strengths for Optically Allowed Transitions

In this paper, we present electron-impact excitation collision strengths and Maxwellian averaged effective collision strengths for the complicated iron-peak ion Cr II. We consider specifically the allowed lines for transitions from the 3d 5 and 3d 44s even parity configuration states to the 3d 44p odd parity configuration levels. The parallel suite of R-Matrix packages, RMATRX II, which have recently been extended to allow for the inclusion of relativistic effects, were used to compute the collision cross sections. A total of 108 LSπ/280 Jπ levels from the basis configurations 3d 5, 3d 44s, and 3d 44p were included in the wavefunction representation of the target including all doublet, quartet, and sextet terms. Configuration interaction and correlation effects were carefully considered by the inclusion of seven more configurations and a pseudo-corrector type orbital. The 10 configurations incorporated into the Cr II model thus listed are 3d 5, 3d 44s, 3d 44p, 3d 34s 2, 3d 34p 2, 3d 34s4p, , , , and , constituting the largest Cr II target model considered to date in a scattering calculation. The Maxwellian averaged effective collision strengths are computed for a wide range of electron temperatures 2000-100,000 K which are astrophysically significant. Care has been taken to ensure that the partial wave contributions to the collision strengths for these allowed lines have converged with top-up from the Burgess-Tully sum rule incorporated. Comparisons are made with the results of Bautista et al. and significant differences are found for some of the optically allowed lines considered.

Electron impact excitation of Fe-peak elements : forbidden transitions in the 3d5 manifold of Fe IV

Electron-impact excitation collision strengths of the Fe-peak element Fe IV are calculated in the close-coupling approximation using the R-matrix suite of codes PRMAT designed for parallel processors. One hundred and eight LS-coupled states arising from the 3d5, 3d44s and 3d44p configurations of Fe IV, are retained in the present calculations. Detailed multi-configuration interaction target wavefunctions are used with the aid of 3p2 → 3d2 electron promotions and a correlation orbital in the present calculations. Effective collision strengths for optically forbidden transitions, which are extremely important in the analysis of lines in the Fe IV spectra, are obtained by averaging the electron collision strengths for a wide range of incident electron energies, over a Maxwellian distribution of velocities. Results are presented for electron temperatures (Te in Kelvin) in the range 3.3 ≤ Log Te≤ 6.0 applicable to many laboratory and astrophysical plasmas for transitions within the 3d5 manifold. The present results compared to previous investigations provide improved results for important lines in the Fe IV spectrum.

Electron impact excitation of Fe III : forbidden transitions

Electron-impact excitation collision strengths of the iron peak element Fe III are calculated in the close-coupling approximation using the new R-matrix program PRMAT designed for present and future generations of parallel processors. In the present calculations 136 LS-coupled states arising from the 3d6, 3d54s and 3d54p configurations of Fe III are retained. The effective collision strengths, which are extremely important in the analysis of astrophysically important lines in the Fe III spectra, are obtained by averaging the electron collision strengths for a wide range of incident electron energies over a Maxwellian distribution of velocities. Results are presented for electron temperatures (Te in Kelvin) in the range 3.3≤log Te≤6.0, applicable to many laboratory and astrophysical plasmas for forbidden transitions within the 3d6 manifold. The present results provide improved results for important lines in the Fe III spectrum.