Electric Dipole Transition Rates Research Articles

Atomic Lifetimes of Astrophysical Interest in Ions of Fe

Multiply charged ions of iron dominate the EUV spectrum of the solar corona. For the interpretation of such spectra, data on both the atomic structure and the transition rate are essential, most of which are provided by theory and computation. The wavelengths of observed spectra are used to test the predicted energy level structure, while the line intensities depend on level lifetimes and branch fractions. A number of electric dipole and higher-order transition rates have been measured over the years in the laboratory, mostly by beam-foil spectroscopy, at heavy-ion storage rings, and at various ion traps. In this paper, the state of the knowledge base on level lifetimes in all ions of Fe is assessed, and the problems of further progress are outlined.

Bottomonium spectroscopy using Coulomb plus linear (Cornell) potential

The Coulomb plus linear (Cornell) potential is used to investigate the mass spectrum of bottomonium. Gaussian wave function is used in position and momentum space to estimate values of potential and kinetic energies, respectively. Based on our calculations, we study newly observed $${\varUpsilon {(10860)}}$$ as an admixture of $$4^{3}S_{1}$$ with $$4^{3}D_{1}$$ and $${\varUpsilon {(10753)}}$$ as an admixture of $$6^{3}S_{1}$$ with $$4^{3}D_{1}$$ ; also, we try to assign $${{\varvec{\Upsilon }}{(11020)}}$$ as a pure $$4^{3}D_{1}$$ bottomonium state. We also study the Regge trajectories in the $$(J,M^{2})$$ and $$(n_r,M^{2})$$ planes to help prove our association. We estimate the pseudoscalar and vector decay constants, the radiative (electric and magnetic dipole) transition rates, and the annihilation decay width for bottomonium states.

Spectral and photophysical modifications of porphyrins attached to core–shell nanoparticles. Theory and experiment

Plasmonic nanostructures, of which gold nanoparticles are the most elementary example, owe their unique properties to localized surface plasmons (LSP), the modes of free electron oscillation. LSP alter significantly electromagnetic field in the nanostructure neighborhood (i.e., near-field), which can modify the electric dipole transition rates in organic emitters. This study aims at investigating the influence of Au@SiO2 core–shell nanoparticles on the photophysics of porphyrins covalently attached to the nanoparticles surface. Guided by theoretical predictions, three sets of gold nanoparticles of different sizes were coated with a silica layer of similar thickness. The outer silica surface was functionalized with either free-base meso-tetraphenylporphyrin or its zinc complex. Absorption and emission bands of porphyrin overlap in energy with a gold nanoparticle LSP resonance that provides the field enhancement. Silica separates the emitters from the gold surface, while the gold core size tunes the energy of the LSP resonance. The signatures of weak-coupling regime have been observed. Apart from modified emission profiles and shortened S1 lifetimes, Q band part intensity of the excitation spectra significantly increased with respect to the Soret band. The results were explained using classical transfer matrix simulations and electronic states kinetics, taking into account the photophysical properties of each chromophore. The calculations could reasonably well predict and explain the experimental outcomes. The discrepancies between the two were discussed.

Experimental study of lifetimes of excited states in the Kπ = 0− octupole band and γ-vibrational band in 228Th

Lifetimes of excited states in the Kπ = 0− octupole band and γ-vibrational of 228Th have been measured using the fast timing setup at the University of the West of Scotland (UWS). The setup consists of two cerium doped LaBr3 fast scintillators placed equidistant from the radioactive source 232Th. The states of interest have been analysed by doing the triple γ – γ – time coincidence analysis and using the fast-timing technique, mirror-symmetric centroid difference method. Octupole collectivity in 228Th nucleus is also investigated by calculating the enhanced electric dipole moments and transition rates in excited states followed by lifetime measurements in octupole band.

Calculation of atomic properties of superheavy elements Z=110–112 and their ions

We calculate the spectra, electric dipole transition rates and isotope shifts of the super heavy elements Ds (Z=110), Rg (Z=111) and Cn (Z=112) and their ions. These calculations were performed using a recently developed, efficient version of the ab initio configuration interaction combined with perturbation theory to treat distant effects. The successive ionization potentials of the three elements are also calculated and compared to lighter elements.

Energies, electric dipole (E1), quadrupole (E2), octupole (E3) and magnetic dipole (M1), quadrupole (M2) transition rates for Ca XII, Ti XIV, Cr XVI, Fe XVIII and Ni XX

Energies, weighted oscillator strengths (gf), line strengths (S) and radiative rates (A) for allowed and forbidden transitions are presented for 2s2p62S1/2 − 2s22p52P1/2, 2P3/2 and 2s22p52P1/2 − 2s22p52P3/2 transitions in fluorine-like Ca XII (Z = 20), Ti XIV (Z = 22), Cr XVI (Z = 24), Fe XVIII (Z = 26) and Ni XX (Z = 28) ions. Moreover, the allowed electric dipole (E1) and the forbidden electric quadrupole (E2), octupole (E3), magnetic dipole (M1) and quadrupole (M2) transition rates for some transitions are obtained. The 2s22p5–2s 2p6-type transitions of F-like ions are prominent in high-temperature plasmas and are useful for diagnostics. The present results are obtained from configuration interaction atomic structure calculations using the code SUPERSTRUCTURE (SS) which includes relativistic effects in Breit–Pauli approximation. The comparison of the present energies with the available observed energies displayed very good agreement (< 1%). The presented excitation energy results have been compared with other detailed relativistic approaches such as Dirac–Fock, coupled cluster and configuration interaction for a few ionic states.

Comparison between 403 nm and 497 nm repumping schemes for strontium magneto-optical traps

The theoretical description of the external degrees of freedom of atoms trapped inside a magneto-optical trap (MOT) often relies on the decoupling of the evolution of the internal and external degrees of freedom. That is possible thanks to much shorter timescales typically associated with the first ones. The electronic structure of alkaline-earth atoms, on the other hand, presents ultra-narrow transitions and metastable states that makes such an approximation invalid in the general case. In this article, we report on a model based on open Bloch equations for the evolution of the number of atoms in a magneto-optical trap. With this model we investigate the loading of the strontium blue magneto-optical trap under different repumping schemes, either directly from a Zeeman slower, or from an atomic reservoir made of atoms in a metastable state trapped in the magnetic quadrupolar field. The fluorescence observed on the strong 461 nm transition is recorded and quantitatively compared with the results from our simulations. The comparison between experimental results and calculations within our model allowed to identify the existence of the decay paths between the upper level of the repumping transition and the dark strontium metastable states, which could not be explained by electric dipole transition rates calculated in the literature. Moreover, our analysis pinpoints the role of the atomic movement in limiting the efficiency of the atomic repumping of the Sr metastable states.

Spectroscopy and decay properties of charmonium

The mass spectra of charmonium are investigated using a Coulomb plus linear (Cornell) potential. Gaussian wave functions in position space as well as in momentum space are employed to calculate the expectation values of potential and kinetic energy respectively. Various experimental states (X(4660)(53S1), X(3872)(23P1), X(3900)(21P1), X(3915)(23P0) and X(4274)(33P1) etc.) are assigned as charmonium states. We also study the Regge trajectories, pseudoscalar and vector decay constants, electric and magnetic dipole transition rates, and annihilation decay widths for charmonium states.

Vector dark matter detection using the quantum jump of atoms

The hidden sector U(1) vector bosons created from inflationary fluctuations can be a substantial fraction of dark matter if their mass is around 10−5 eV. The creation mechanism makes the vector bosons' energy spectral density ρcdm/ΔE very high. Therefore, the dark electric dipole transition rate in atoms is boosted if the energy gap between atomic states equals the mass of the vector bosons. By using the Zeeman effect, the energy gap between the 2S state and the 2P state in hydrogen atoms or hydrogen like ions can be tuned. The 2S state can be populated with electrons due to its relatively long life, which is about 1/7 s. When the energy gap between the semi-ground 2S state and the 2P state matches the mass of the cosmic vector bosons, induced transitions occur and the 2P state subsequently decays into the 1S state. The 2P→1S decay emitted Lyman-α photons can then be registered. The choices of target atoms depend on the experimental facilities and the mass ranges of the vector bosons. Because the mass of the vector boson is connected to the inflation scale, the proposed experiment may provide a probe to inflation.

Radiative Decay Rates for Electric Dipole, Magnetic Dipole and Electric Quadrupole Transitions in Triply Ionized Thulium (Tm IV)

A new set of radiative decay parameters (oscillator strengths, transition probabilities) for spectral lines in triply ionized thulium (Tm IV) has been obtained within the framework of the pseudo-relativistic Hartree-Fock (HFR) approach. The effects of configuration interaction and core-polarization have been investigated in detail and the quality of the results has been assessed through a comparison between different HFR physical models. The spectroscopic data listed in the present paper cover electric dipole as well as magnetic dipole and electric quadrupole transitions in a wide range of wavelengths from extreme ultraviolet to near infrared.

EXTENDED CALCULATIONS WITH SPECTROSCOPIC ACCURACY: ENERGY LEVELS AND TRANSITION PROPERTIES FOR THE FLUORINE-LIKE ISOELECTRONIC SEQUENCE WITH Z = 24–30

ABSTRACT We have performed extensive multiconfiguration Dirac–Hartree–Fock calculations and second-order many-body perturbation calculations for F-like ions with Z = 24–30. Energy levels and transition rates for electric dipole (E1), electric-quadrupole (E2), electric-octupole (E3), magnetic dipole (M1), and magnetic-quadrupole (M2) transitions, as well as radiative lifetimes, are provided for the lowest 200 levels belonging to the , , , , , and configurations of each ion. The results from the two sets of calculations are in excellent agreement. Extensive comparisons are also made with other theoretical results and observed data from the CHIANTI and NIST databases. The present energies and wavelengths are believed to be accurate enough to aid line identifications involving the n = 3 and n = 4 configurations, for which observations are largely missing. The calculated wavelengths and transition data will be useful in the modeling and diagnostics of astrophysical and fusion plasmas.

Influence of Optical Properties of Ag NPs from Raphanus sativus Leaf Extract on Lanthanide Complexes

Simple rapid green synthesis route using Raphanus sativus leaf extract as reducing and stabilizing agent produced silver nanoparticles (Ag NPs) at room temperature. The formation of Ag NPs has been characterized and confirmed through TEM, XRD, FTIR and UV-visible absorption spectrum. Luminescence enhancement was observed only for few particular concentrations of Eu3+ and Sm3+ ions in Ag NPs. Enhancement of luminescence might be due to the increase in the electric dipole transition rate with the variation of local environment surrounding Ln3+ ions. Lifetimes of Ln3+ ions were found to increase with increase in Ag NP concentration to certain extent but found to decrease with further increase in Ag NPs. Nonlinear absorption behaviours in the picosecond (ps) and femtosecond (fs) time domains were studied by using the Z-scan technique. Third-order susceptibility was measured with ultrafast nonlinear optical response in the fs regime by using degenerate four-wave mixing (DFWM). High luminescence enhancement factors and good nonlinear optical properties of the biosynthesized Ag NPs have applications in biology and optics.

High-multipole excitations of hydrogen-like atoms by twisted photons near a phase singularity

We calculate transition amplitudes and cross sections for excitation of hydrogen-like atoms by the twisted photon states, or photon states with angular momentum projection on the direction of propagation exceeding ℏ. If the target atom is located at distances of the order of atomic size near the phase singularity in the vortex center, the transition rates into the states with orbital angular momentum become comparable with the rates for electric dipole transitions. It is shown that when the transition rates are normalized to the local photon flux, the resulting cross sections for are singular near the optical vortex center. The relation to the ‘quantum core’ concept introduced by Berry and Dennis is discussed.

Energy levels, oscillator strengths, line strengths, and transition probabilities in Si-like ions of La XLIII, Er LIV, Tm LV, and Yb LVI

Detailed calculations using the multi-configuration Dirac–Fock (MCDF) method are carried out for the lowest 64 fine-structure levels of the 3s23p2, 3s23p3d, 3s3p3, 3s3p23d, 3s23d2, and 3p4 configurations in Si-like ions of La XLIII, Er LIV, Tm LV, and Yb LVI. Energies, oscillator strengths, wavelengths, line strengths, and radiative electric dipole transition rates are given for all ions. A parallel calculation using the many-body perturbation theory (MBPT) method is also carried out to assess the present energy levels accuracy. Comparisons are performed between these two sets of energy levels, as well as with other available results, showing that they are in good agreement with each other within 0.5%. These high accuracy results can be used to the modeling and the interpretation of astrophysical objects and fusion plasmas.

Wide-angle energy-momentum spectroscopy.

Light emission is defined by its distribution in energy, momentum, and polarization. Here, we demonstrate a method that resolves these distributions by means of wide-angle energy-momentum spectroscopy. Specifically, we image the back focal plane of a microscope objective through a Wollaston prism to obtain polarized Fourier-space momentum distributions, and disperse these two-dimensional radiation patterns through an imaging spectrograph without an entrance slit. The resulting measurements represent a convolution of individual radiation patterns at adjacent wavelengths, which can be readily deconvolved using any well-defined basis for light emission. As an illustrative example, we use this technique with the multipole basis to quantify the intrinsic emission rates for electric and magnetic dipole transitions in europium-doped yttrium oxide (Eu³⁺:Y₂O₃) and chromium-doped magnesium oxide (Cr³⁺:MgO). Once extracted, these rates allow us to reconstruct the full, polarized, two-dimensional radiation patterns at each wavelength.

Relativistic many-body calculation of energies, transition rates, lifetimes, and multipole polarizabilities in Cs-like La iii

Excitation energies of the [Xe]$nd$ ($n=5\ensuremath{-}9$), [Xe]$ns$ ($n=6\ensuremath{-}10$), [Xe]$np$ ($n=6\ensuremath{-}9$), [Xe]$nf$ ($n=4\ensuremath{-}8$), and [Xe]$ng$ ($n=5\ensuremath{-}8$) states in La iii, where [Xe] = $1{s}^{2}2{s}^{2}2{p}^{6}3{s}^{2}3{p}^{6}3{d}^{10}4{s}^{2}4{p}^{6}4{d}^{10}5{s}^{2}5{p}^{6}$, are evaluated. Electric dipole matrix elements for the allowed transitions between the low-lying [Xe]$nd$, [Xe]$ns$, [Xe]$np$, [Xe]$nf$, and [Xe]$ng$ states in the La iii ion are calculated using the high-precision relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Recommended values are provided for a large number of electric dipole matrix elements, oscillator strengths, transition rates, and lifetimes. Scalar and tensor polarizabilities of the states listed above are evaluated. The uncertainties of the recommended values are estimated. Electric quadrupole and magnetic dipole matrix elements are calculated to determine lifetimes of the $5{d}_{5/2}$ and $6s$ metastable levels. The ground-state $E1$, $E2$, and $E3$ static polarizabilities are calculated. This work provides recommended values critically evaluated for their accuracy for a number of La iii atomic properties for use in planning and analysis of various experiments as well as theoretical modeling.

Calculations with spectroscopic accuracy: energies, transition rates, and LandégJ-factors in the carbon isoelectronic sequence from Ar XIII to Zn XXV

Extensive self-consistent multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations and subsequent relativistic configuration interaction calculations are performed for 262 states belonging to the 15 configurations 2s 2 2p 2 ,2 s2p 3 ,2 p 4 ,2 s 2 2p3l, 2s2p 2 3l ,2 p 3 3l and 2s 2 2p4l (l = 0, 1, 2) in selected carbon-like ions from Ar XIII to Zn XXV. Electron correlation effects are accounted for through large configuration state function expansions. Calculated energy levels are compared with existing theoretical calculations and data from the Chianti and NIST databases. In addition, Lande gJ-factors and radiative electric dipole transition rates are given for all ions. The accuracy of the calculations are high enough to facilitate the identification of observed spectral lines.

Theoretical study on K, L, and M X-ray transition energies and rates of neptunium and its ions

The transition energies and electric dipole (E1) transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac—Fock (MCDF) method. In the calculations, the contributions from Breit interaction and quantum electrodynamics (QED) effects (vacuum polarization and self-energy), as well as nuclear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1+ to Np6+ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.

Plasmonically Enhanced Optical Characteristics From Europium Organometallic Complex

We demonstrated that the plasmonic effect can enhance the photoluminescence of the europium organometallic complex in conventional organic light emitting diodes stack from an anode to emissive layer with solution processing. The aggregated gold nanoparticles (A-Au NPs) were incorporated in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) layer to increase the luminescent quantum efficiency of the emissive layer. An enhancement of 31% was achieved in the emission intensity at 614 nm for samples with A-Au NPs. The reduced exciton lifetime measured by time-resolved photoluminescence comply with the Purcell effect. These improvements are attributed to the localized surface plasmon of A-Au NPs increasing the electric dipole transition rate from Eu3+ ions.

On the role of atomic metastability in the production of Balmer line radiation from ‘cold’ atomic hydrogen, deuterium and hydrogenic ion impurities in fusion edge plasmas**This manuscript is dedicated to the memory of my esteemed colleague Dr. rer. nat. Manfred Korten (1940–2010).

Published arguments, which assign an important role to atomic metastability in the production of ‘narrow’ Zeeman component radiation from the boundary region of fusion plasmas, are examined critically in relation to l-redistribution by proton and electron collisions, and mixing of unperturbed atomic states by the ion microfield and microfield gradient. It is concluded that these important processes indeed severely constrain the contribution from ‘metastable’ states to the generation of the hydrogen Balmer spectra, for electron concentrations above 1012 cm−3, as pointed out before by the present author (Hey et al 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3555). The analysis of collision-induced l-redistribution represents an extension of that used previously (Hey et al 1996 Contrib. Plasma Phys. 36 583), applicable up to higher electron densities. For comparison purposes, we also consider the question of metastability of ionized helium in a low-temperature plasma, and that of some common hydrogenic impurities (C5+ and Ne9+) in a hydrogen (deuterium) fusion plasma. While for low nuclear charge Z the metastability of 2s1/2 levels is quenched by the plasma environment, it is much reduced in high-Z ions owing to the rapid increase with Z of the two-photon electric dipole (2E1) and magnetic dipole (M1) spontaneous transition rates to the ground state, whereas the role of the plasma in these cases is less important. The main new principle elaborated in this work is the sensitivity of atomic line strengths, and hence collision strengths, to perturbation by the plasma environment for transitions between fine-structure sublevels of the same principal quantum number. As the plasma microfield strength grows, ‘allowed’ transitions diminish in strength, while ‘forbidden’ transitions grow. However, owing to violation of the parity selection rule, there is an overall loss of collision strength available to transitions, resulting from the appearance of significant ‘self-strength’ contributions, in accord with the sum rules for the line strengths, which remain valid over the range of fields considered. Thus, the relative effectiveness per perturber of both electron and ion collisions, for inducing population transfer between fine-structure sublevels, diminishes as the sublevels evolve from a fine-structure dominated to a Stark-effect-dominated regime. In the concluding discussion, we mention that this finding may have a bearing on discrepancies claimed between Stark broadening theory developed by Griem (1967 Astrophys. J. 148 547) and by Watson (2006 J. Phys.B: At. Mol. Opt. Phys. 39 1889), and the measurements of Bell and co-workers (2000 Publ. Astron. Soc. Pac. 112 1236; 2011 Astrophys. Space Sci. 335 451) for high-n radio recombination lines from galactic H II regions. In the absence of detailed modelling to test this suggestion, however, it would be premature to attempt to draw any firm conclusions along these lines.