Claire Hudson

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.

Effective collision strengths for electron impact excitation of C II

We extend a previous calculation of effective collision strengths for electron impact excitation of the boron-like ion C . The earlier work was restricted to the excitation within the 2s 2 2p ground configuration and the sixteen 2s 2 2p-2s2p 2 fine-structure transitions whilst the present paper considers all fine-structure transitions among the levels arising from the lowest 16 LS states. The collisional cross sections are computed in the multichannel close-coupling R-matrix approximation, in which sophisticated configuration-interaction wave functions are used to represent the target states. The 16 states included have the following basis configurations: the 2s 2 2p ground state, four 2s2p 2 states, three 2p 3 states, one 2s2p3s state as well as the 2s 2 3l(l = s, p, d) and 2s 2 4l(l = s, p, d, f) states. The 16 LS target states correspond to 30 fine-structure levels and lead to a total of 435 fine-structure transitions. In this paper we tabulate effective collision strengths, obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities, for electron temperatures in the range given by log10 Te(K) = 3.0−5.5, suitable for most astrophysical applications and laboratory plasma diagnostics. Significant differences from a previous calculation are noted and comparisons are made with some recent experimental data.

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.

ELECTRON-IMPACT EXCITATION COLLISION STRENGTHS AND THEORETICAL LINE INTENSITIES FOR TRANSITIONS IN S III

We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S III over a wide range of electron temperatures of astrophysical importance, log Te (K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations—3s 23p 2, 3s3p 3, 3s 23p3d, 3s 23p4s, 3s 23p4p, and 3s 23p4d—giving rise to 1378 individual lines and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code CLOUDY to generate line intensities for a range of plasma parameters, with emphasis on allowed ultraviolet extreme-ultraviolet emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by Far-Ultraviolet Spectroscopic Explorer and Extreme-Ultraviolet Explorer. The present line intensities are found to agree well with the observational results and provide a noticeable improvement on the values predicted by CHIANTI.

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.

Dirac R-matrix collision strengths and effective collision strengths for transitions of Nixvii

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

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.

Electron impact excitation of the Fe-peak ions Ni III and Ni IV

Accurate determination of electron excitation rates for the Fe-peak elements is complicated by the presence of an open 3d-shell in the description of the target ion, which can lead to hundreds of target state energy levels. Furthermore, the low energy scattering region is dominated by series of Rydberg resonances, which require a very fine energy mesh for their delineation. These problems have prompted the development of a suite of parallel R-matrix codes. In this work we report recent applications of these codes to the study of electron impact excitation of Ni III and Ni IV.

Electron-Impact Excitation of Fe-peak Ions for Astrophysical Applications

This paper discusses one of the major outstanding problems in atomic collision physics, namely the accurate theoretical treatment of electron scattering from open d-shell systems, and explores how this issue has been addressed over recent years with the development of the new parallel R-matrix suite of codes. It focuses on one code in particular – the new parallel R-matrix package PRMAT, which has recently been extended to account for relativistic fine-structure effects. This program facilitates the determination of accurate electron-impact excitation rates for complex open 3d-shell systems including the astrophysically important Fe-peak ions such as Ni II, Fe II and Fe III. Results are presented for collision strengths and Maxwellian averaged effective collision strengths for the optically forbidden fine-structure transitions of Ni II. To our knowledge this is the most extensive calculation completed to date for this ion.