Energy levels and radiative rates for transitions in Ti X

We report calculations of energy levels, radiative rates, oscillator strengths and line strengths for transitions among the lowest 345 levels of Ti X. These include 146 levels of the n 3 configurations and 86 of 3s ²4ℓ, 3s²5ℓ and 3s3p4ℓ, plus some of the 3s²6ℓ, 3p²4ℓ and 3s3p5ℓ levels. The general-purpose relativistic atomic structure package and flexible atomic code are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 345 levels, although calculations have been performed for a much larger number of levels. Comparisons are made with existing results and the accuracy of the data is assessed. Additionally, lifetimes for all 345 levels are listed. Extensive comparisons of lifetimes are made for the lowest 40 levels, for which discrepancies with recent theoretical work are up to 30%. Discrepancies in lifetimes are even larger, up to a factor of four, for higher excited levels. Furthermore, the effect of large configuration interaction (CI) is found to be insignificant for both the energies and lifetimes for the lowest 40 levels of Ti X which belong to the 3s²3p, 3s3p², 3s²3d, 3p³ and 3s3p3d configurations. However, the contribution of CI is more appreciable for the energy levels and radiative rates among higher excited levels. Our listed energy levels are estimated to be accurate to better than 1% (within 0.1 Ryd), whereas results for other parameters are probably accurate to better than 20%. © 2013 The Royal Swedish Academy of Sciences.

Photoionization cross sections for O-like S IX: a Breit-Pauli R-matrix calculation

In this paper we present photoionization cross sections for the lowest five states of O-like S IX (1s(2)2s(2)2p(4) P-3(0,1,2), D-1(2), S-1(0)). The relativistic Breit-Pauli R-matrix codes were utilized including all terms of the 2s(2)2p(3), 2s2p(4), 2p(5), 2s(2)2p(2)3s, 3p, 3d and 2s2p(3)3s, 3p, 3d configurations in the expansion of the collision wavefunction for S X. It was also found that to achieve convergence of the low-lying energy separations of the target levels, an additional 21 configuration functions needed to be included in the configuration interaction expansion, incorporating two-electron excitations from the 2s and 2p shells to the 3s, 3p and 3d shells. The present work thus constitutes the most sophisticated photoionization evaluation for ground and metastable levels of the S IX ion. Direct comparisons have been made with the only available data found on the OPEN-ADAS database between level resolved contributions of the spectrum. This comparison for the background cross section exhibits excellent agreement at all photon energies for each partial photoionization cross section contribution investigated. Finally, the autoionizing bound states arising from numerous open channels have also been investigated and identified using the QB approach, a procedure for analyzing resonances in atomic and molecular collision theory which exploits the analytic properties of R-matrix theory. Major Rydberg resonance series are also presented and tabulated for the dominant linewidths considered.

Towards a spectroscopically accurate set of potentials for heavy hydride laser cooling candidates: effective core potential calculations of BaH

BaH (and its isotopomers) is an attractive molecular candidate for laser cooling to ultracold temperatures and a potential precursor for the production of ultracold gases of hydrogen and deuterium. The theoretical challenge is to simulate the laser cooling cycle as reliably as possible and this paper addresses the generation of a highly accurate ab initio $^{2}\Sigma^+$ potential for such studies. The performance of various basis sets within the multi-reference configuration-interaction (MRCI) approximation with the Davidson correction (MRCI+Q)is tested and taken to the Complete Basis Set (CBS) limit. It is shown that the calculated molecular constants using a 46 electron Effective Core-Potential (ECP) and even-tempered augmented polarized core-valence basis sets (aug-pCV$n$Z-PP, n= 4 and 5) but only including three active electrons in the MRCI calculation are in excellent agreement with the available experimental values. The predicted dissociation energy De for the X$^2\Sigma^+$ state (extrapolated to the CBS limit) is 16895.12 cm$^{-1}$ (2.094 eV), which agrees within 0.1$\%$ of a revised experimental value of <16910.6 cm$^{-1}$, while the calculated re is within 0.03 pm of the experimental result.

Dirac R -matrix calculations of electron-impact excitation of neon-like krypton

We have employed the Dirac R -matrix method to determine electron-impact excitation cross sections and effective collision strengths in Ne-like Kr 26+ . Both the configuration-interaction expansion of the target and the close-coupling expansion employed in the scattering calculation included 139 levels up through n = 5. Many of the cross sections are found to exhibit very strong resonances, yet the effects of radiation damping on the resonance contributions are relatively small. Using these collisional data along with multi-configuration Dirac–Fock radiative rates, we have performed collisional-radiative modeling calculations to determine line-intensity ratios for various radiative transitions that have been employed for diagnostics of other Ne-like ions.

An R -matrix with pseudo-states calculation of electron-impact excitation in C 2 +

We have performed an R-matrix with pseudo-states (RMPS) calculation of electron-impact excitation in C2+.Collision strengths and effective collision strengths were determined for excitation between the lowest 24 terms, including all those arising from the 2s3l and 2s4l configurations. In the RMPS calculation, 238 terms (90 spectroscopic and 148 pseudo-state) were employed in the close-coupling (CC) expansion of the target. In order to investigate the significance of coupling to the target continuum and highly excited bound states, we compare the RMPS results with those from an R-matrix calculation that incorporated all 238 terms in the configuration- interaction expansion, but only the lowest 44 spectroscopic terms in the CC expansion. We also compare our effective collision strengths with those from an earlier 12-state R-matrix calculation (Berrington et al 1989 J. Phys. B: At.Mol. Opt. Phys. 22 665). The RMPS calculation was extremely large, involving (N +1)-electron Hamiltonian matrices of dimension up to 36 085, and required the use of our recently completed suite of parallel R-matrix programs. The full set of effective collision strengths fromourRMPS calculation is available at theOakRidgeNationalLaboratoryControlledFusion Atomic Data Center web site. 1.

Vibrational excitation of the N2+ first negative (0,0), (1,0) and (2,0) bands by electron impact: a theoretical study using the R-matrix approach

Ab initio cross section calculations for vibronic excitation using the R -matrix approach have been performed on the N 2 + molecular ion complex. A three-state close-coupling expansion is used where the electronic target states; X 2 g + , A 2 u and B 2 u + of the molecular cation are represented by a valence configuration-interaction approximation. A non-adiabatic approximation is invoked to study vibronic excitation for the first three negative bands, (0,0), (1,0) and (2,0) of the X-B transition (B 2 u + v ´ X 2 g + v ´´ ) of N 2 + . Fixed-nuclei and non-adiabatic cross section results are compared with the available experimental data for the (0,0) band and the breakdown of the adiabatic fixed-nuclei approximation is clearly evident for the vibronic excitation of the (1,0) and (2,0) bands in this molecular ion complex.

The 2p interloper resonances in collisions

Ab initio electron scattering calculations using the R -matrix approach have been performed for within a three-state valence configuration-interaction model (VCI). The lowest three electronic target states ( , and the ) of this molecular nitrogen cation are included in the close-coupling method, with each state being represented by a valence CI approximation. From a detailed analysis of the resonance structure found in our work for the symmetries we find four prominent Rydberg series of the type , , , and a interloper resonance. This interloper molecular resonance associated with the B state of is seen to cause distortions of the resulting resonance spectra. A comparison of our total cross sections for the X - B transition shows excellent agreement with the available experimental data.

Rates of E1, E2, M1, and M2 transitions in Ni II

Aims. We present rates for all E1, E2, M1, and M2 transitions among the 295 fine-structure levels of the configurations 3d⁹, 3d⁸4s, 3d⁷4s², 3d⁸4p, and 3d⁷4s4p, determined through an extensive configuration interaction calculation. 

Methods. The CIV3 code developed by Hibbert and coworkers is used to determine for these levels configuration interaction wave functions with relativistic effects introduced through the Breit-Pauli approximation. 

Results. Two different sets of calculations have been undertaken with different 3d and 4d functions to ascertain the effect of such variation. The main body of the text includes a representative selection of data, chosen so that key points can be discussed. Some analysis to assess the accuracy of the present data has been undertaken, including comparison with earlier calculations and the more limited range of experimental determinations. The full set of transition data is given in the supplementary material as it is very extensive. 

Conclusions. We believe that the present transition data are the best currently available.

Inner-shell photodetachment of excited 4S° and 6S° metastable bound states of Be-

The total cross sections for photodetachment of the metastable 1s ²2p^{3 4}S° and 1s2s2p^{3 6}S° excited bound states of the negative ion of beryllium are presented for a range of initial photon energies across and beyond the 1s detachment threshold. A multichannel close-coupling R-matrix approximation is used to compute the cross sections, with sophisticated configuration-interaction wavefunctions being used to represent the initial and final states. At present there are no other theoretical or experimental data available with which to compare the cross sections for these two photodetachment processes.

Effective collision strengths for election impact excitation of Cl III

Effective collision strengths for electron-impact excitation of the phosphorus-like ion Cl III are presented for all fine-structure transitions among the levels arising from the lowest 23 LS states. The collisional cross sections are computed in the multichannel close-coupling R-matrix approximation, where sophisticated configuration-interaction wave functions are used to represent the target states. The 23 LS states are formed from the basis configurations 3s²3p³, 3s3p⁴, 3s²3p²3d, and 3s²3p²4s, and correspond to 49 fine-structure levels, leading to a total possible 1176 fine-structure transitions. The effective collision strengths, obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities, are tabulated in this paper for all 1176 transitions and for electron temperatures in the ranges T(K)=7500-25,000 and log T(K)=4.4-5.4. The former range encompasses the temperatures of particular importance for application to gaseous nebulae, while the latter range is more applicable to the study of solar and laboratory-type plasmas. © 2001 Academic Press.

Effective collision strengths for fine-structure forbidden transitions among the 2s22p3 levels of S x

Effective collision strengths for electron-impact excitation of the N-like ion S x are calculated in the close-coupling approximation using the multichannel R-matrix method. Specific attention is given to the 10 astrophysically important fine-structure forbidden transitions among the ⁴S^O, ²D^o and ²P^o levels in the 2s²2p³ ground configuration. The total (e^- + ion) wavefunction is expanded in terms of the 11 lowest LS eigenstates of S x, and each eigenstate is represented by extensive configuration-interaction wavefunctions. The collision strengths obtained are thermally averaged over a Maxwellian distribution of velocities, for all 10 fine-structure transitions, over the range of electron temperatures log T(K) = 4.6-6.7 (the range appropriate for astrophysical applications). The present effective collision strengths are the only results currently available for these fine-structure transition rates.

Level-resolved quantum statistical theory of electron capture into many-electron compound resonances in highly charged ions

The strong mixing of many-electron basis states in excited atoms and ions with open f shells results in very large numbers of complex, chaotic eigenstates that cannot be computed to any degree of accuracy. Describing the processes which involve such states requires the use of a statistical theory. Electron capture into these “compound resonances” leads to electron-ion recombination rates that are orders of magnitude greater than those of direct, radiative recombination and cannot be described by standard theories of dielectronic recombination. Previous statistical theories considered this as a two-electron capture process which populates a pair of single-particle orbitals, followed by “spreading” of the two-electron states into chaotically mixed eigenstates. This method is similar to a configuration-average approach because it neglects potentially important effects of spectator electrons and conservation of total angular momentum. In this work we develop a statistical theory which considers electron capture into “doorway” states with definite angular momentum obtained by the configuration interaction method. We apply this approach to electron recombination with W²⁰⁺, considering 2×10⁶ doorway states. Despite strong effects from the spectator electrons, we find that the results of the earlier theories largely hold. Finally, we extract the fluorescence yield (the probability of photoemission and hence recombination) by comparison with experiment.

Energy levels and radiative rates for Cr-like Cu VI and Zn VII

Energy levels and radiative rates (. A-values) for transitions in Cr-like Cu VI and Zn VII are reported. These data are determined in the quasi-relativistic approach (QR), by employing a very large configuration interaction (CI) expansion which is highly important for these ions. No radiative rates are available in the literature to compare with our results, but our calculated energies are in close agreement with those compiled by NIST and other available theoretical data, for a majority of the levels. The A-values (and resultant lifetimes) are listed for all significantly contributing E1, E2 and M1 radiative transitions among the energetically lowest 322 levels of each ion.

Radiative rates for E1, E2, M1, and M2 transitions in S-like to F-like tungsten ions (W LIX to W LXVI)

Calculations of energy levels, radiative rates and lifetimes are reported for eight ions of tungsten, i.e. S-like (W LIX) to F-like (W LXVI). A large number of levels have been considered for each ion and extensive configuration interaction has been included among a range of configurations. For the calculations, the general-purpose relativistic atomic structure package (. grasp) has been adopted, and radiative rates (as well as oscillator strengths and line strengths) are listed for all E1, E2, M1, and M2 transitions of the ions. Comparisons have been made with earlier available experimental and theoretical energies, although these are limited to only a few levels for most ions. Therefore for additional accuracy assessments, particularly for energy levels, analogous calculations have been performed with the flexible atomic code (. fac).

Radiative rates for E1, E2, M1, and M2 transitions in Br-like ions with 43≤Z≤50

Energies and lifetimes are reported for the eight Br-like ions with 43≤Z≤50, namely Tc IX, Ru X, Rh XI, Pd XII, Ag XIII, Cd XIV, In XV, and Sn XVI. Results are listed for the lowest 375 levels, which mostly belong to the 4s²4p⁵, 4s²4p⁴4ℓ, 4s4p⁶,4s²4p⁴5ℓ, 4s²4p³4d², 4s4p⁵4ℓ, and 4s4p⁵5ℓ configurations. Extensive configuration interaction among 39 configurations (generating 3990 levels) has been considered and the general-purpose relativistic atomic structure package (grasp) has been adopted for the calculations. Radiative rates are listed for all E1, E2, M1, and M2 transitions involving the lowest 375 levels. Previous experimental and theoretical energies are available for only a few levels of three, namely Ru X, Rh XI and Pd XII. Differences with the measured energies are up to 4% but the present results are an improvement (by up to 0.3 Ryd) in comparison to other recently reported theoretical data. Similarly for radiative rates and lifetimes, prior results are limited to those involving only 31 levels of the 4s²4p⁵, 4s²4p⁴4d, and 4s4p⁶ configurations for the last four ions. Moreover, there are generally no discrepancies with our results, although the larger calculations reported here differ by up to two orders of magnitude for a few transitions.