Electron impact excitation of S-like iron

Energy levels and radiative rates for transitions among the lowest 48 fine-structure levels belonging to the (1s(2) 2s(2) 2p (6)) 3s (2)3p (4) , 3s3p(5), 3s (2)3p (3) 3d and 3p(6) configurations of Fe xi have been calculated using the fully relativistic grasp code. Additionally, collision strengths for transitions among these levels have also been computed using the Dirac Atomic R-matrix Code (darc) of Norrington & Grant. Radiative rates and oscillator strengths are tabulated for all allowed transitions among the 48 fine-structure levels, while collision strengths are reported at three energies above thresholds, i.e. 8, 16 and 24 Ryd for a few representative transitions. Furthermore, excitation rates have been calculated in a wide electron temperature range below 5 x 10(6) K, and the contribution of resonances has been included in the threshold regions. Comparisons are made with the earlier available theoretical and experimental rates, and it is concluded that the experimental rates are overestimated by up to a factor of 2.

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

Aims.
In this paper we report calculations for energy levels, radiative rates, and electron impact excitation rates for transitions in O vii.
Methods.
The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative
rates. For determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) and the
flexible atomic code (fac) are used.
Results.
Oscillator strengths, radiative rates, and line strengths are reported for all E1, E2, M1, and M2 transitions among the lowest
49 levels of O vii. Collision strengths have been averaged over a Maxwellian velocity distribution, and the resulting effective collision
strengths are reported over a wide temperature range below 2 × 106 K. Additionally, lifetimes are also listed for all levels.
Key words.

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 $\le$ 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 (107.7 K). Comparisons are made with earlier available results and the accuracy of the data is assessed.

Absolute photoionization cross sections for Xe4+, Xe5+, and Xe6+ near 13.5 nm: Experiment and theory

Absolute photoionization cross-section measurements for a mixture of ground and metastable states of Xe4+, Xe5+, and Xe6+ are reported in the photon energy range of 4d -> nf transitions, which occur within or adjacent to the 13.5 nm window for extreme ultraviolet lithography light source development. The reported values allow the quantification of opacity effects in xenon plasmas due to these 4d -> nf autoionizing states. The oscillator strengths for the 4d -> 4f and 4d -> 5f transitions in Xeq+ (q=1-6) ions are calculated using nonrelativistic Hartree-Fock and random phase approximations. These are compared with published experimental values for Xe+ to Xe3+ and with the values obtained from the present experimental cross-section measurements for Xe4+ to Xe6+. The calculations assisted in the determination of the metastable content in the ion beams for Xe5+ and Xe6+. The experiments were performed by merging a synchrotron photon beam generated by an undulator beamline of the Advanced Light Source with an ion beam produced by an electron cyclotron resonance ion source.

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Li II, Be III, B IV and C V

We report calculations for energy levels, radiative rates and electron impact excitation rates for transitions in He-like Li II, Be III, B IV and C V. grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Collision strengths have been averaged over a Maxwellian velocity distribution and the effective collision strengths so obtained are reported over a wide temperature range up to 10(6) K. Comparisons have been made with similar data obtained from the flexible atomic code (FAC) to highlight the importance of resonances, included in calculations from darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, particularly for weak transitions and at low energies, have also been discussed. Additionally, lifetimes are also listed for all calculated levels of the above four ions.

Energy levels, radiative rates and electron impact excitation rates for transitions in Si XII, Si XIII and Si XIV

In this paper, we report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in Li-like Si XII, He-like Si XIII and H-like Si XIV. The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 24 levels of Si XII, 49 levels of Si XIII and 25 levels of Si XIV, belonging to the n≤5 configurations. Collision strengths have been averaged over a Maxwellian electron velocity distribution and the effective collision strengths so obtained are reported over a wide temperature range below 107 K. Comparisons have been made with similar data obtained from the flexible atomic code (fac) to highlight the importance of resonances, included in calculations from darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, particularly for weak transitions and at low energies, are also discussed. Additionally, lifetimes are listed for all calculated levels of the above three ions, although no measurements are available with which to compare.

Energy levels, radiative rates and electron impact excitation rates for transitions in H-like N VII, O VIII, F IX, Ne X and Na XI

We report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in H-like N VII, O VIII, F IX, Ne X and Na XI. The general-purpose relativistic atomic structure package (grasp) is adopted for calculating energy levels and radiative rates, while the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC) are used for determining the collision strengths and subsequently the excitation rates. Oscillator strengths, radiative rates and line strengths are listed for all E1, E2, M1 and M2 transitions among the lowest 25 levels of the above five ions. Collision strengths have been averaged over a Maxwellian velocity distribution, and the effective collision strengths so obtained are reported over a wide temperature range below 10(7) K. Additionally, lifetimes are also given for all the calculated energy levels of the above five ions.

Energy levels, radiative rates and electron impact excitation rates for transitions in Li-like N V, F VII, Ne VIII and Na IX

In this paper, we report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in Li-like N V, F VII, Ne VIII and Na IX. The general-purpose relativistic atomic structure package (GRASP) is adopted for calculating energy levels and radiative rates, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC) are used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 24 levels of N V, F VII, Ne VIII and Na IX. Collision strengths have been averaged over a Maxwellian velocity distribution and the effective collision strengths so obtained are reported over a wide temperature range below 10(6.6) K. Additionally, lifetimes are also reported for all calculated levels of the above four ions.

Energy levels and radiative rates for transitions in B-like to F-like Xe ions (Xe L-XLVI)

Energy levels, radiative rates, oscillator strengths, line strengths, and lifetimes have been calculated for transitions in B-like to F-like Xe ions, Xe L–XLVI. For the calculations, a fully relativistic grasp code has been adopted, and results are reported for all electric dipole, electric quadrupole, magnetic dipole, and magnetic quadrupole transitions among the lowest 125, 236, 272, 226, and 113 levels of Xe L, Xe XLIX, Xe XLVIII, Xe XLVII, and Xe XLVI, respectively, belonging to the n ⩽ 3 configurations.

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 (1s22s22p6) 3s23p5, 3s3p6, 3s23p43d, 3s3p53d, 3s23p33d2, 3s3p43d2, 3p63d, and 3s23p44 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 105.0−106.6 K.

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX.

We report calculations of energy levels, radiative rates and electron impact excitation cross
sections and rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX. The grasp
(general-purpose relativistic atomic structure package) is adopted for calculating energy levels
and radiative rates. To determine the collision strengths and subsequently the excitation rates,
the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line
strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of
each ion. Collision strengths are averaged over a Maxwellian velocity distribution and the
effective collision strengths obtained listed over a wide temperature range up to 107.4 K.
Comparisons are made with similar data obtained from the flexible atomic code (fac) to
highlight the importance of resonances, included in calculations with darc, in the
determination of effective collision strengths. Discrepancies between the collision strengths
from darc and fac, particularly for forbidden transitions, are also discussed. Additionally,
theoretical lifetimes are listed for all the 49 levels of the above four ions.

Energy levels, wavefunction compositions and electric dipole transitions in neutral Ca

A configuration-interaction approach, based on the use of B-spline basis sets combined with a model potential including monoelectronic and dielectronic core polarization effects, is employed to calculate term energies and wavefunctions for neutral Ca. Results are reported for singlet and triplet bound states, and some quasi-bound states above the lowest ionization limit, with angular momentum up to L = 4. Comparison with experiment and with other theoretical results shows that this method yields the most accurate energy values for neutral Ca obtained to date. Wavefunction compositions, necessary for labelling the levels, and the effects of semi-empirical polarization potentials on the wavefunctions are discussed, as are some recent identifications of doubly-excited states. It is shown that taking into account dielectronic core polarization changes the energies of the lowest terms in Ca significantly, in general by a few hundred cm(-1), the effect decreasing rapidly for the higher bound states. For Rydberg states with n approximate to 7 the accuracy of the results is often better than a few cm(-1). For series members (or perturbers) with a pronounced 3d character the error can reach 150 cm(-1). The wavefunctions are used to calculate oscillator strengths and lifetimes for a number of terms and these are compared with existing measurements. The agreement is good but points to a need for improved measurements.

On the required shape corrections to the local density and generalized gradient approximations to the Kohn-Sham potentials for molecular response calculations of (hyper)polarizabilities and excitation energies

It is well known that shape corrections have to be applied to the local-density (LDA) and generalized gradient (GGA) approximations to the Kohn-Sham exchange-correlation potential in order to obtain reliable response properties in time dependent density functional theory calculations. Here we demonstrate that it is an oversimplified view that these shape corrections concern primarily the asymptotic part of the potential, and that they affect only Rydberg type transitions. The performance is assessed of two shape-corrected Kohn-Sham potentials, the gradient-regulated asymptotic connection procedure applied to the Becke-Perdew potential (BP-GRAC) and the statistical averaging of (model) orbital potentials (SAOP), versus LDA and GGA potentials, in molecular response calculations of the static average polarizability alpha, the Cauchy coefficient S-4, and the static average hyperpolarizability beta. The nature of the distortions of the LDA/GGA potentials is highlighted and it is shown that they introduce many spurious excited states at too low energy which may mix with valence excited states, resulting in wrong excited state compositions. They also lead to wrong oscillator strengths and thus to a wrong spectral structure of properties like the polarizability. LDA, Becke-Lee-Yang-Parr (BLYP), and Becke-Perdew (BP) characteristically underestimate contributions to alpha and S-4 from bound Rydberg-type states and overestimate those from the continuum. Cancellation of the errors in these contributions occasionally produces fortuitously good results. The distortions of the LDA, BLYP, and BP spectra are related to the deficiencies of the LDA/GGA potentials in both the bulk and outer molecular regions. In contrast, both SAOP and BP-GRAC potentials produce high quality polarizabilities for 21 molecules and also reliable Cauchy moments and hyperpolarizabilities for the selected molecules. The analysis for the N-2 molecule shows, that both SAOP and BP-GRAC yield reliable energies omega(i) and oscillator strengths f(i) of individual excitations, so that they reproduce well the spectral structure of alpha and S-4.(C) 2002 American Institute of Physics.

Radiative rates for E1, E2, M1, and M2 transitions in the Br-like ions Sr IV, Y V, Zr VI, Nb VII, and Mo VIII

Energies and lifetimes are reported for the lowest 375 levels of five Br-like ions, namely SrIV, YV, ZrVI, NbVII, and MoVIII, mostly belonging to the 4s²4p⁵, 4s²4p⁴4ℓ, 4s4p⁶, 4s²4p⁴5ℓ, 4s²4p³4d², 4s4p⁵4ℓ, and 4s4p⁵5ℓ configurations. Extensive configuration interaction has been included and the general-purpose relativistic atomic structure package (grasp) has been adopted for the calculations. Additionally, radiative rates are listed among these levels for all E1, E2, M1, and M2 transitions. From a comparison with the measurements, the majority of our energy levels are assessed to be accurate to better than 2%, although discrepancies between theory and experiment for a few are up to 6%. An accuracy assessment of the calculated radiative rates (and lifetimes) is more difficult, because no prior results exist for these ions.

Energy levels, radiative rates and lifetimes for transitions in Br-like ions with 38 ≤ Z ≤ 42

Energy levels and radiative rates for transitions in five Br-like ions (Sr IV, Y V, Zr VI, Nb VII and Mo VIII) are calculated with the general-purpose relativistic atomic structure package (GRASP). Extensive configuration interaction has been included and results are presented among the lowest 31 levels of the 4s²4p⁵, 4s²4p⁴4d and 4s4p⁶ configurations. Lifetimes for these levels have also been determined, although unfortunately no measurements are available with which to compare. However, recently theoretical results have been reported by Singh et al (2013 Phys. Scr. 88 035301) using the same GRASP code. But their reported data for radiative rates and lifetimes cannot be reproduced and show discrepancies of up to five orders of magnitude with the present calculations.