C.Y. Chen

Systematic Calculations of Energy Levels and Transition Rates of Be-like Ions with Z=10–30 Using a Combined Configuration Interaction and Many-body Perturbation Theory Approach

We report calculations of energy levels and radiative rates for transitions among the lowest 116 fine-structure levels arising from the configurations in Be-like ions with Z = 10–30. The wavelengths, oscillator strengths, line strengths, and radiative rates for all possible electric dipole, magnetic dipole, electric quadrupole, and magnetic quadrupole transitions among the 116 levels have been calculated using the combined configuration interaction and many-body perturbation method. The accuracy of the results is determined through extensive comparisons with existing laboratory measurements and theoretical results. The present complete set of results should be of great help in line identification and the interpretation of spectra, as well as in the modeling and diagnostics of astrophysical and fusion plasmas.

Relativistic many-body calculations on wavelengths and transition probabilities for forbidden transitions within the

Wavelengths and transition probabilities have been computed for forbidden lines within the 3dk(k = 1-9) ground configurations in ions of hafnium, tantalum, tungsten and gold, employing the second-order relativistic many-body perturbation theory (RMBPT). For comparison, the relativistic configuration-interaction (RCI) calculations have also been performed. Comparing to the previously published theoretical wavelengths and the present RCI ones, the present RMBPT results are in much better agreement with the experimental values measured recently by using the electron beam ion trap facility, reproducing these observed wavelengths to within 0.2% for all transitions only with one exception. In addition, it removes dramatically the systematic underestimation/overestimation for shorter/longer wavelengths existing in the present RCI and other calculations.

3{{{\rm d}}^{k}}

Energy levels and transition rates for electric-dipole (E1), electric-quadrupole (E2), magnetic-dipole (M1), and magnetic-quadrupole (M2) transitions among the lowest 159 levels arising from the configurations in Kr XXV are calculated through two state-of-the-art methods, i.e. second-order many-body perturbation theory (MBPT) and multi-configuration Dirac-Fock (MCDF) method. In the latter calculation, valence-valence and the 2p, 2s core-valence correlations are taken into account. A parallel calculation using the standard relativistic configuration-interaction (RCI) method is also carried out to assess the improvement from the inclusion of second-order many-body perturbation. The present MBPT and MCDF results are compared with available experimental and other theoretical values. They are believed to be the most comprehensive and accurate ones to date.

ground configurations in Co- through K-like ions of hafnium, tantalum, tungsten and gold

Spectroscopy in the wavelength region of 330 nm to 400 nm for highly charged tungsten was performed using the High Temperature Super Conducting Electron Beam Ion Trap (SH-HtscEBIT) at Fudan University. Three lines from palladium-like tungsten (W28+) were identified as transitions between metastable levels in the first excited configuration ([Kr]4d94f). A second-order relativistic many-body perturbation theory approach and a simple collisional radiative model were used to theoretically study the fine structure levels of the 4d94f configuration. The calculated results show qualitative agreement with experiment. We conclude that some levels in the 4d94f excited configuration have extremely long lifetimes and may exhibit extraordinarily high populations, possibly leading to indirect ionization in, for example, fusion plasmas.

Energy levels and transition rates for Mg-like Kr XXV

Extensive self-consistent multi-configuration Dirac-Hartree-Fock (MCDHF) calculations are performed for the 3s23p63d k (k = 1-9) ground configurations of highly charged ions (Z = 72-83). Complete and consistent datasets of excitation energies, wavelengths, line strengths, oscillator strengths, and magnetic dipole (M1) and electric quadrupole (E2) transition rates among all these levels are given. We have compared our results with the results available in the literature and the accuracy of the data is assessed. We predict new energy levels and transition probabilities where no other experimental or theoretical results are available, which will form the basis for future experimental work.

Investigation of transitions between metastable levels of the first excited configuration of palladium-like tungsten

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 Ef = 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.5, where Ef 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 × Z2 and 2 × 106 × Z2 K. We believe that the present results are the most extensive and definitive atomic dataset to date for highly charged H-like ions.

Multi-configuration Dirac–Hartree–Fock calculations of forbidden transitions within the 3dk ground configurations of highly charged ions (Z=72–83)

In this paper we report the calculations on effective collision strengths for electron impact excitations among the 41 levels of 3s23p3, 3s3p4 and 3s23p23d configurations in Ni XIV. The Dirac R-matrix theory and the relativistic distorted-wave method in conjunction with isolated resonance approximation are adopted for the calculations. Detailed comparisons between the results obtained from the above two methods show that the independent process and isolated resonance approximation using distorted waves can describe the near threshold resonances reasonably well for most transitions in Ni XIV, though channel-coupling effects are found to be important for weak transitions. Resonances enlarge significantly the effective collision strengths for many transitions, even by over two orders of magnitude.

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

Visible transitions of promethium-like tungsten (W13+) were studied using the Shanghai high temperature superconducting electron beam ion trap. The M1 transition between the ground state (4f135s2 2F) fine structure levels was measured to be at 549.95 ± 0.06 nm. Seven other lines from W13+ were also found and five of them were classified as belonging to transitions within the first excited configuration (4f125s25p). These lines were assigned with the help of relativistic configuration interaction calculations and collisional-radiative model predictions of the relative line intensities.

Electron impact excitation for P-like Ni XIV

We reported the relative responsivity calibration of the grazing-incidence flat-field EUV spectrometer between 175 and 435 A by means of two methods. The first method is implemented by measuring the diffraction efficiency of the grating with synchrotron radiation light source. Considering the transmission efficiency and quantum efficiency of the other optical components in the spectrometer, the total responsivity was then obtained. The second one was carried out by measuring line emissions from C3+, N4+ and O3+ ions at Shanghai high temperature super conductor electron beam ion trap (SH-HtscEBIT). The EUV spectra were also simulated theoretically via a collisional radiative model. In the calculation, the second-order relativistic many-body perturbation theory approach based on the flexible atomic code was used to calculate the energy levels and transition rates; the close-coupling R-matrix approach and relativistic distorted wave method were utilized to calculate the collision strength of electron impact ...

Experimental and theoretical study of visible transitions in promethium-like tungsten

The fully relativistic multiconfiguration Dirac--Hartree--Fock method is used to compute excitation energies and lifetimes for the 143 lowest states of the