Jon Grumer

Energy levels and radiative data for Kr-like W38+ from MCDHF and RMBPT calculations

Energies, transition rates, line strengths and lifetimes have been computed for all levels of the 4p 6 and 4p 54d configurations of W38+ by using the multi-configuration Dirac-Hartree-Fock (MCDHF) method as well as relativistic many-body perturbation theory. We investigate systematically correlation, relativistic and quantum electro-dynamical (QED) effects of different properties, including excitation energies and transition rates. We demonstrate that it is important to include the core-valence correlation of rather deep subshells (including 3d and 3p) to reach close to spectroscopic accuracy for the transition energies. We also show that high-multipole transitions (E3, M2) are important for the lifetime of some metastable levels of 4p 54d (). The present results are in good agreement with experiments and of considerably higher accuracy than those achieved in previous theoretical works.

Effect of an external magnetic field on the determination of E1M1 two-photon decay rates in Be-like ions

In this work we report on ab initio theoretical results for the magnetic-field-induced 2s 2p P-3(0) -> 2s(2) S-1(0) E1 transition for ions in the beryllium isoelectronic sequence between Z = 5 and 92. It has been proposed that the rate of the E1M1 two-photon transition 2s 2p P-3(0) -> 2s(2) S-1(0) can be extracted from the lifetime of the P-3(0) state in Be-like ions with zero nuclear spin by employing resonant recombination in a storage ring. This experimental approach involves a perturbing external magnetic field. The effect of this field needs to be evaluated in order to properly extract the two-photon rate from the measured decay curves. The magnetic-field-induced transition rates are carefully evaluated, and it is shown that, with a typical storage-ring field strength, it is dominant or of the same order as the E1M1 rate for low-and mid-Z ions. Results for several field strengths and ions are presented, and we also give a simple Z-dependent formula for the rate. We estimate the uncertainties of our model to be within 5% for low-and mid-Z ions and slightly larger for more highly charged ions. Furthermore we evaluate the importance of including both perturber states, P-3(1) and P-1(1), and it is shown that excluding the influence of the P-1(1) perturber overestimates the rate by up to 26% for the mid-Z ions. (Less)

A Novel Method to Determine Magnetic Fields in Low-density Plasma Facilitated Through Accidental Degeneracy of Quantum States in Fe9+

We propose a new method to determine magnetic fields, by using the magnetic-field-induced electric dipole transition 3p(4) 3d D-4(7/2) -> 3p(5) P-3/2 in Fe9+ ions. This ion has a high abundance in astrophysical plasma and is therefore well suited for direct measurements of even rather weak fields in, e.g., solar flares. This transition is induced by an external magnetic field and its rate is proportional to the square of the magnetic field strength. We present theoretical values for what we will label the reduced rate and propose that the critical energy difference between the upper level in this transition and the close-to-degenerate 3p(4) 3d D-4(5/2) should be measured experimentally since it is required to determine the relative intensity of this magnetic line for different magnetic fields. (Less)

ATOMIC-LEVEL PSEUDO-DEGENERACY of ATOMIC LEVELS GIVING TRANSITIONS INDUCED by MAGNETIC FIELDS, of IMPORTANCE for DETERMINING the FIELD STRENGTHS in the SOLAR CORONA

We present a measured value for the degree of pseudo-degeneracy between two fine-structure levels in Fe9+ from line intensity ratios involving a transition induced by an external magnetic field. The extracted fine-structure energy difference between 3p4 3d 4D7/2 the and 4D7/2 levels, where the latter is the upper state for the magnetic-field induced line, is needed in our recently proposed method to measure magnetic-field strengths in the solar corona. The intensity of the 3p4 3d 4D7/2 → 3p5 2 P3/2 line at 257.262 A is sensitive to the magnetic field external to the ion. This sensitivity is in turn strongly dependent on the energy separation in the pseudo-degeneracy through the mixing induced by the external magnetic field. Our measurement, which uses an Electron Beam Ion Trap with a known magnetic-field strength, indicates that this energy difference is 3.5 cm-1. The high abundance of Fe9+ and the sensitivity of the lines transition probability to field strengths below 0.1 T opens up the possibility of diagnosing coronal magnetic fields. We propose a new method to measure the magnetic field in the solar corona, from similar intensity ratios in Fe9+. In addition, the proposed method to use the line ratio of the blended line 3p4 3d 4D7/2.5/2 → 3p5 2P3/2 with another line from Fe x as the density diagnostic should evaluate the effect of the magnetic-field-induced transition line. (Less)

Unexpected transitions induced by spin-dependent, hyperfine and external magnetic-field interactions

Unexpected transitions are induced by weaker interactions not included in the gross structure model of the ion under investigation. We discuss different examples of such decay channels, starting with relativistic spin-induced transitions. These represented an important field of study a few decades ago, and we illustrate how some challenging cases can be treated very accurately with todayʼs computational techniques, while close degeneracy sometimes still prevents ab initio methods from obtaining accurate results. For hyperfine induced transitions we review some recent results and discuss remaining challenges for experiment and theory. Finally, we discuss the newly opened field of accurate calculations for transitions induced by an external magnetic field and point to some examples of where these are accessible for experimental tests.

HYPERFINE-DEPENDENT gf -VALUES OF Mn i LINES IN THE 1.49–1.80 μm H BAND

The three Mn I lines at 17325, 17339, and 17349 angstrom are among the 25 strongest lines (log(gf) > 0.5) in the H band. They are all heavily broadened due to hyperfine structure, and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infrared (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines cannot be described in the conventional way using the diagonal A and B hyperfine interaction constants. The off-diagonal hyperfine interaction not only has a large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and the gf-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, we achieved agreement between our synthetic and experimental spectra. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modeled in the relevant region, 1.73-1.74 mu m, using our theoretically predicted gf-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and gf-values for all the 3d(5)4s(S-7)4d e(6)D - 3d(5)4s(S-7)4f w(6)F hyperfine lines are available as supporting material, whereas only the stronger lines are presented and discussed in detail in this paper.

Hyperfine induced intensity redistribution in In II

We present a theoretical investigation of the hyperfine structure of the 5s5d D-3(2)-5s4f F-3(2,3)0 transitions in In II. Earlier work has failed in determining hyperfine constants for the upper levels of these transitions. We show that this is due to strong off-diagonal hyperfine interaction, which not only changes the position of the individual hyperfine lines but also introduces large intensity redistributions among the different hyperfine levels. We present hyperfine dependent gf-values and show that off-diagonal hyperfine interaction reduces some of the gf-values by two orders of magnitude, while others are increased by up to more than a factor of 6. We also discuss the influence on the hyperfine structure of an accurate representation of the level-splitting of the 5s4f configuration. We show that the hyperfine interaction in F-3(3)0 and F-1(3)0 is very hard to determine accurately even in a large-scale calculation, and we derive a semi-empirical method for adjusting our results using an experimentally known, diagonal hyperfine constant for 5s4f F-1(3)0. The resulting theoretical synthetic spectra reproduce the experimental values to high accuracy and facilitate the identification of all observed lines. (Less)

Resolving a discrepancy between experimental and theoretical lifetimes in atomic negative ions

A recent measurement of the lifetime of the excited 3p5 state in the S- negative ion, which is dominated by a forbidden magnetic dipole transition to the 2 P3/ 2 ground state, reveals a discrepancy with earlier theoretical predictions. To investigate this we have performed systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations for this system. After including a careful treatment of correlation and relativistic effects, we predict a well-converged value for this lifetime, with an uncertainty considerably less than 1%, thereby removing the apparent conflict between theory and experiment. We also show that this result corresponds to the non-relativistic limit in the LS coupling approximation for the magnetic dipole transition within this 2 P term. In addition we demonstrate the usefulness of the latter approach for 2 P transitions in O-, Se- and Te-, as well as for analogous M1 transitions within 2 D terms in Ni- and Pt- ions.

Magnetic field induced transition rates in Ne- and Be-like ions for plasma diagnostics and E1M1 two-photon decay rate determination

XXVII International Conference on Photonic, Electronic and Atomic Collisions, Lanzhou, China, 24-30 July, 2013.

The M1 ground state fine structure transition in Ag-like Yb

In our previous work, the agreement between the theoretical and measured wavelength for the 4f-M1 transition of Ag-like W shed light on the importance of a careful treatment of all core-valence correlation effects to obtain a reliable value of this fine structure energy separation. To confirm these results and extend the analysis isoelectronically, we have undertaken an experimental and theoretical study of the same M1 transition in Ag-like Yb. The measured wavelength for this M1 transition is 515.77 +/- 0.10 nm (515.91 nm in vacuum) which agrees well with our ab initio theoretical value of 515.48 nm.