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The energy transfer dynamics of the biohybrid photosynthetic antenna complexes were investigated by transient absorption. The mechanism of energy transfer was discussed in terms of the higher-lying exciton state of bacteriochlorophyll aggregates.

The change in the positron annihilation lifetime (PAL) of vacancy clusters before and after electrolysis hydrogen charging was determined using PAL measurements in electron-irradiated F82H. The experimental change indicated 8 hydrogen atoms were trapped in vacancy clusters; whereas the theoretical calculation resulted in approximately 14 atoms. As the samples were left at room temperature for 5 min until the start of the PAL measurements, the de-trapping effect of hydrogen atoms was also considered; approximately 13 hydrogen atoms were captured at each vacancy cluster. The PAL decreased after annealing at 148 K, which could not be explained theoretically. Therefore, further experiments and discussions are needed to obtain a precise change in the PAL of vacancy clusters containing hydrogen atoms in F82H.

To provide spectroscopic data for W13+, the present work is focused on the analysis of spectra observed in the visible range, using a compact electron beam ion trap (CoBIT). Line identification is done by using a collisional radiative model, along with sophisticated structure calculations from FAC and GRASP2018. Most of the identified lines belong to magnetic dipole (M1) transitions between the levels of the 4f125p1 and 4f13 configurations.

We investigate the effect of the presence of lanthanides (Z = 57- 71) on the kilonova at t~hours after the neutron star merger for the first time. For this purpose, we calculate the atomic structures and the opacities for selected lanthanides: Nd (Z = 60), Sm (Z = 62), and Eu (Z = 63). We consider the ionization degree up to tenth (XI), applicable for the ejecta at t ~ a few hours after the merger, when the temperature is T ~ 10^5 K. We find that the opacities for the highly ionized lanthanides are exceptionally high, reaching k_exp~1000 cm^2/g for Eu, due to the highly dense energy levels. Using the new opacity, we perform radiative transfer simulations to show that the early light curves become fainter by a (maximum) factor of four, in comparison to lanthanide-free ejecta at t~0.1 day. However, the period at which the light curves are affected is relatively brief due to the rapid time evolution of the opacity in the outermost layer of the ejecta. We predict that for a source at a distance of ~100 Mpc, UV brightness for lanthanide-rich ejecta shows a drop to ~21-22 mag at t~0.1 day and the UV peaks around t~0.2 day with a magnitude of ~19 mag. Future detection of such a kilonova by the existing UV satellite like Swift or the upcoming UV satellite ULTRASAT will provide useful constraints on the abundance in the outer ejecta and the corresponding nucleosynthesis conditions in the neutron star mergers., 18 pages, 7 figures, accepted to ApJ

In the neutron-star mergers, the radioactive decay of freshly synthesized heavy elements produces emissions in the ultraviolet-optical-infrared range, producing a transient called kilonova. The observational properties of the kilonova depend on the bound-bound opacity of the heavy elements, which was largely unavailable for the conditionssuitable at an early time (t < day). In this article, I share some of our recent progress on modeling the early kilonova light curve, focusing on the atomic opacity calculation.

Coalescence of binary neutron stars gives rise to kilonova, thermal emission powered by radioactive decays of newly synthesized r-process nuclei. Observational properties of kilonova are largely affected by bound-bound opacities of r-process elements. It is, thus, important to understand atomic properties of heavy elements to link the observed signals with nucleosynthesis of neutron star mergers. In this paper, we introduce the latest status of kilonova modeling by focusing on the aspects of atomic physics. We perform systematic atomic structure calculations of r-process elements to understand element-to-element variation in the opacities. We demonstrate that the properties of the atomic structure of heavy elements are imprinted in the opacities of the neutron star merger ejecta and consequently in the kilonova light curves and spectra. Using this latest opacity dataset, we briefly discuss implications for GW170817, expected diversity of kilonova emission, and prospects for element identification in kilonova spectra.

The observations of GW170817/AT2017gfo have provided us with evidence that binary neutron star mergers are sites of $r$-process nucleosynthesis. However, the observed signatures in the spectra of GW170817/AT2017gfo have not been fully decoded especially in the near-infrared (NIR) wavelengths. In this paper, we investigate the kilonova spectra over the entire wavelength range with the aim of elemental identification. We systematically calculate the strength of bound-bound transitions by constructing a hybrid line list that is accurate for important strong transitions and complete for weak transitions. We find that the elements on the left side of the periodic table, such as Ca, Sr, Y, Zr, Ba, La, and Ce, tend to produce prominent absorption lines in the spectra. This is because such elements have a small number of valence electrons and low-lying energy levels, resulting in strong transitions. By performing self-consistent radiative transfer simulations for the entire ejecta, we find that La III and Ce III appear in the NIR spectra, which can explain the absorption features at $\lambda\sim 12000$-14000 A in the spectra of GW170817/AT2017gfo. The mass fractions of La and Ce are estimated to be $>2\times 10^{-6}$ and $\sim$ (1-100)$\times 10^{-5}$, respectively. An actinide element Th can also be a source of absorption as the atomic structure is analogous to that of Ce. However, we show that Th III features are less prominent in the spectra because of the denser energy levels of actinides compared to those of lanthanides., Comment: 23 pages, 19 figures, 5 tables, accepted for publication in ApJ

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.

Tungsten is suitable for wall material as well as divertor material in magnetic fusion devices due to its low sputtering and good thermal properties. The electron impact ionization process in the low charged states of W is important for modeling of the divertors. We present results of our calculation for the electron induced total ionization cross sections of $$\hbox {W}^{\mathrm {+}}$$ . The direct ionization cross sections have been calculated in variants of the binary encounter Bethe methods as well as variants of the distorted wave approximation. The individual cross sections for the direct ionization of some outer subshells of $$\hbox {W}^{\mathrm {+}}$$ are also reported, and it is observed that the major contribution to the total cross section comes from the 5d, 6s and 4f subshells. Present cross section results have been compared with the available measurements and theoretical results.

The nebular phase of lanthanide-rich ejecta of a neutron star merger (NSM) is studied by using a one-zone model, in which the atomic properties are represented by a single species, neodymium (Nd). Under the assumption that beta-decay of r-process nuclei is the heat and ionization source, we solve the ionization and thermal balance of the ejecta under non-local thermodynamic equilibrium. The atomic data including energy levels, radiative transition rates, collision strengths, and recombination rate coefficients, are obtained by using atomic structure codes, GRASP2K and HULLAC. We find that both permitted and forbidden lines roughly equally contribute to the cooling rate of Nd II and Nd III at the nebular temperatures. We show that the kinetic temperature and ionization degree increase with time in the early stage of the nebular phase while these quantities become approximately independent of time after the thermalization break of the heating rate because the processes relevant to the ionization and thermalization balance are attributed to two-body collision between electrons and ions at later times. As a result, in spite of the rapid decline of the luminosity, the shape of the emergent spectrum does not change significantly with time after the break. We show that the emission-line nebular spectrum of the pure Nd ejecta consists of a broad structure from $0.5\,\mu m$ to $20\,\mu m$ with two distinct peaks around $1\,\mu m$ and $10\,\mu m$., Comment: 20 pages, 18 figures, submitted to MNRAS

A new calculation of atomic kinetics of multiple-charged tungsten ions in a high temperature plasma in the non-local thermodynamic equilibrium (nLTE) based on the Markov chain Monte-Carlo (MCMC) method is presented. It is shown that the fractional ion abundance and the resulting mean charge of the plasma can be calculated with much lower computational time compared to conventional methods. The present method can be easily parallelized and is applicable to larger problems, such as modeling coupled atomic processes and radiation hydrodynamics.

Special Issue: Proceedings of the 19th International Conference on the Physics of Highly Charged Ions (HCI 2018), Caparica, Lisboa, Portugal, 3‐7 September 2018. The electron beam ion source (Kobe EBIS) has been developed to perform modification of surfaces using highly charged ions (HCIs) at the Kobe University, Japan. Recent study revealed that periodic intermission of electron beam improves charge state distribution of extracted ions. The period of intermission is in the order of 100 ms, and the width of beam-off time is 1 ms or less. This operational mode (pulse mode) makes it possible to produce Ar15+ to Ar17+ effectively, whereas the charge is limited less than 14+ under the ordinary operational mode with direct current (DC) electron beam. A spike of HCIs with a peak current in the order of nA is also observed at each moment of electron beam off. The measurement of the time evolution of Ar16+ intensity around the timing of mode change revealed that the intensity of extracted Ar16+ changes slowly after mode change with a time constant of few seconds.

Strong radiative cooling by tungsten ions in the core plasma is one of issues in fusion reactors. Quantitative analysis of tungsten density in divertor plasma, scrape-off layer, and main plasma relies on accuracy of spectroscopic model of tungsten ions. We have developed a collisional-radiative (CR) model for tungsten ions to estimate line intensities of tungsten ions and also have measured tungsten spectra in wide wavelength region from extreme ultraviolet (EUV) to visible wavelengths simultaneously in the Large Helical Device (LHD) with tungsten pellet injection to validate the CR model for tungsten ions. So-called unresolved transition array (UTA) measured in EUV spectra at 4.5–7 nm are commonly seen in fusion plasmas with electron temperature of around 1 keV, which corresponds to edge temperature in ITER. The UTA is strong and largely contributes to the radiation power at this temperature, so the CR model calculation is required to reproduce the UTA to estimate the tungsten radiation power. We have developed the CR model to include recombination processes, which were not considered before for tungsten ions, as a hybrid model with fine-structure levels and configuration-averaged levels for W25+–W39+ ions. The 6 nm-peak of UTA is not still reproduced well, but the recombination processes and cascade from higher levels can enhance spectral intensities. Contribution of dielectronic recombination from the excited states of W28+ ions is examined but it is small for W27+ ions. The spectral profiles of n = 4–5 transition peaks at 2–4 nm do not change much with recombination processes. Analysis of measured EUV spectra in LHD plasma shows that tungsten is accumulated first into core plasma to produce hollow temperature distribution due to large radiation power of tungsten ions, and continuous NBI heating recovers central electron temperature and the UTA appears again in EUV spectra with weaker intensity than one at the earlier phase. Reduced intensity of UTA and electron temperature estimated from EUV spectra indicate that tungsten is transported outward and the amount of tungsten emitting EUV spectra is reduced to about 1/4.

Magnetic-dipole (M1) lines of W29+~W39+ were successfully observed in the vacuum-ultraviolet (VUV) wavelength range of 500–900 A in the Large Helical Device (LHD). Tungsten ions are distributed in the NBI-heated LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. It is found that W37+ line at 646.7 A and W38+ lines at 532.9 A and 559.1 A are emitted when the central electron temperature ranges from 2 to 3 keV with relatively high intensity and isolated from other intrinsic impurity lines. The result is the first observation of the M1 forbidden lines of tungsten ions in the VUV wavelength range in fusion plasma experiments. Observation of the W37+ and W38+ lines could improve the tungsten diagnostics in ITER edge plasmas because they are expected to be distributed in the edge plasmas around the last closed flux surface including the scrape-off layer in ITER.

The electron induced processes on tungsten (W) and related materials are of prime importance for the fusion plasma application purposes. W and tungsten based materials have been recommended as the plasma facing components such as walls and divertors in the current fusion devices. We report electron impact total ionization cross sections (TICS) for the W atoms. We also report the direct ionization cross sections for the 4f, 5d, 5p and 6s sub shells of the ground state W. The ionization cross sections have been calculated in the variants of distorted wave approximation (DWA) using Hartree-Fock wavefunctions and distorted potential. We have also calculated ionization cross sections in simpler modified Kim and modified Khare models with scaling laws. Present TICS results have been compared with the other available theoretical results. Reasonable agreement with the existing theoretical results have been obtained for the TICS of W atoms by present distorted wave and BEB approaches. The majority of contribution to the total ionization cross section comes from the direct ionization of 6s and 5d subshells.

International audience; We observed electronic K x rays emitted from muonic iron atoms using superconducting transition-edge sensor microcalorimeters. The energy resolution of 5.2 eV in FWHM allowed us to observe the asymmetric broad profile of the electronic characteristic Kα and Kβ x rays together with the hypersatellite Khα x rays around 6 keV. This signature reflects the time-dependent screening of the nuclear charge by the negative muon and the L-shell electrons, accompanied by electron side feeding. Assisted by a simulation, these data clearly reveal the electronic K- and L-shell hole production and their temporal evolution on the 10–20 fs scale during the muon cascade process.

Lanthanide elements play important roles as an opacity source in the ejected material from neutron star mergers. Accurate and complete atomic data are necessary to evaluate the opacities and to analyze the observed data. In this paper, we perform extended, ab-initio atomic calculations from Pr II (Z=59) to Gd II (Z=64). By using multiconfiguration Dirac-Hartree-Fock and relativistic configuration-interaction methods, implemented in the general-purpose relativistic atomic structure package GRASP2K, we calculate the energy levels and transition data of electric dipole transitions. These computations are based on strategies (with small variations) of Nd II published by Gaigalas et al. (2019). Accuracy of data is evaluated by comparing computed energy levels with the NIST database or other works. For the energy levels, we obtain the average relative accuracy of 8%, 12%, 6%, 8%, and 7% for Pr II, Pm II, Sm II, Eu II, and Gd II ions, respectively as compared with the NIST data. Accuracy of energy transfer to the wavelength as 3%, 14% and 11% for Pr II, Eu II and Gd II. Our computed E1 type transition probabilities are in good agreement with experimental values presented by other authors especially for strong transitions., 20 pages, 14 tables, 11 figures

The wavelength and rate of the $5p\ensuremath{-}5s$ transition of W xiv--W xvi ions have been calculated by the relativistic configuration interaction method with the implementation of the flexible atomic code. A reasonable collisional-radiative model has been constructed to simulate the $5p\ensuremath{-}5s$ transition spectrum of W xiv--W xvi ions, which had been observed in the electron beam ion trap device. The results are in reasonable agreement with the available experimental and theoretical data, which might be applied to identify the controversial spectra. The confusion on the assignment of the ionization stage is solved in the present work.

Aims. We present extensive energy level and transition data for the Ce IV spectrum. By providing accurate atomic data, we evaluate the impact of atomic data on the opacity in the neutron star merger ejecta. Methods. We performed energy spectra and transition data calculations using the GRASP2018 package, which is based on the multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods, and the HULLAC code, which is based on a parametric potential method. Results. We present energy spectra calculated for the 225 levels for the Ce3+ ion. Energy levels are compared with recommended values from the NIST Atomic Spectra Database and other available works. The root-mean-square (rms) deviations obtained for the GRASP2018 energy levels of the 5p6nl configurations from the NIST data are 1270 cm−1. The rms deviations for the HULLAC results from the NIST data are 5780 cm−1. Furthermore, electric dipole (E1) transition data, line strengths, weighted oscillator strengths, and transition rates are computed between the above levels. The computed transition rates are compared with other theoretical computations. We also evaluate the accuracy of the wave functions and transition parameters by analyzing the dependencies of the line strength S on the gauge parameter G. The gauge dependency method also allows us to determine the transitions for which the ratio between the Babushkin and Coulomb gauges shows real agreement between forms and the transitions for which the agreement between both gauges is random. Using the GRASP2018 and HULLAC data, the opacities in the neutron star merger ejecta are also calculated. We find that the opacity of Ce IV is higher than that presented by previous works, which is because of the higher completeness of our atomic data. Although the differences in the energy levels and transition probabilities cause different features in the opacity spectrum, the Planck mean opacities of both data sets agree within 20%.

A detailed level collisional-radiative model of the E1 transition spectrum of Ca-like W$^{54+}$ ion has been constructed. All the necessary atomic data has been calculated by relativistic configuration interaction (RCI) method with the implementation of Flexible Atomic Code (FAC). The results are in reasonable agreement with the available experimental and previous theoretical data. The synthetic spectrum has explained the EBIT spectrum in 29.5-32.5 \AA ,, while several new strong transitions has been proposed to be observed in 18.5-19.6 \AA , for the future EBIT experiment with electron density $n_e$ = $10^{12}$ cm$^{-3}$ and electron beam energy $E_e$ = 18.2 keV.

Calculations of energy levels, radiative data and lifetimes are reported for tungsten Ca-like ion (W LV) by using multi-configuration Dirac–Fock (MCDF) method. The GRASP2K package is adopted to carry out a large-scale systematic computation with a restricted active space treatment; the Breit interaction and QED effects are included in subsequent relativistic configuration interaction calculations. The energies and lifetimes of the lowest 119 levels are listed; the main leading configuration of the levels is of the ground state configuration [Ne]3s 2 3p 6 3d 2 and the first excited configuration [Ne]3s 2 3p 5 3d 3 . The wavelengths, radiative rates and oscillator strengths for relatively strong E1, E2, M1, and M2 transitions are listed. Comparisons with earlier experimental and theoretical values are made. The average relative deviations of energy levels from the NIST results and E1 transition wavelengths from the EBIT experimental results have turned to be only 0.20% and 0.13%, respectively. The other present results are in reasonable agreement with available data. These agreements confirm the reliability and accuracy of the current results. The present datasets may help us with the investigation of the electron–electron correlation effects in complex multi-electron highly charged heavy ions and of the diagnosis of tungsten impurity plasmas in fusion science.

In this work, we continue large-scale ab initio computations for single ionized lanthanides. Extended atomic calculations for the set of ions from Pr ii (Z = 59) to Gd ii (Z = 64) have been performed in our previous work. In this study, ions from Tb ii (Z = 65) to Yb ii (Z = 70) are analyzed. By employing the same multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods that are implemented in the general-purpose relativistic atomic structure package GRASP2018, the energy levels and transition data of electric dipole (E1) transitions are computed. These computations are based on the strategies (with small variations) of Paper I. Accuracy of data is evaluated by comparing the computed energy levels with the data provided by the National Institute of Standards and Technology (NIST) database and with data from various methods. We obtain the average accuracy in the energy level compared with the NIST database: 6%, 5%, 4%, 5%, 3%, and 3% for Tb ii, Dy ii, Ho ii, Er ii, Tm ii, and Yb ii, respectively. We also provide extensive comparison of transition probabilities and wavelengths. Our results reach the average accuracy of transition wavelengths: 9%, 9%, 9%, 3%, 4%, and 11% for Tb ii, Dy ii, Ho ii, Er ii, Tm ii, and Yb ii, respectively.