Excited Ionic States Research Articles

Giant retardation effect in electron-electron interaction

In electron-electron interactions in electromagnetic systems, retardation in the exchange of a virtual photon is essentially important as the first-order quantum electrodynamics correction. However, the retardation effect is generally so small that it is buried in unretarded electric and magnetic interactions and thus has yet to be directly probed. Here, we present a giant contribution of the retardation effect in an electron-electron interaction via observing strong electric-dipole-allowed radiative transition rates. The relative transition rates are obtained for two dominant radiative transitions from the $1s2{s}^{2}2{p}_{1/2}2{p}_{3/2}$ inner-shell excited state of boronlike tungsten and bismuth ions to $1{s}^{2}2{s}^{2}2{p}_{1/2}$ and $1{s}^{2}2{s}^{2}2{p}_{3/2}$, and it was found that the transition rate ratio between the two transitions is affected by the retardation effect up to more than 100%.

Adaptive Algorithm for the Generation of Superconfigurations in Hot-Plasma Opacity Calculations

In hot plasmas, such as the ones encountered in astrophysics or laser-fusion studies, the number of ionic excited states may become huge, and the relevant electron configurations cannot always be handled individually. The Super Transition Array approach enables one to calculate the massic photo-absorption cross-section (or radiative opacity) in a statistical manner consisting of grouping configurations close in energy into superconfigurations. One of the main issues of the method, beyond its spectral resolution, is the determination of the most relevant configurations that contribute to opacity. In this work, we discuss different aspects of the generation of superconfigurations in a hot plasma and propose a new adaptive algorithm.

Shannon Entropy in LS-Coupled Configuration Space for Ni-like Isoelectronic Sequence.

The Shannon entropy in an LS-coupled configuration space has been calculated through a transformation from that in a jj-coupled configuration space for a Ni-like isoelectronic sequence. The sudden change of Shannon entropy, information exchange, eigenlevel anticrossing, and strong configuration interaction have been presented for adjacent levels. It is shown that eigenlevel anticrossing is a sufficient and necessary condition for the sudden change of Shannon entropy, and both of them are a sufficient condition for information exchange, which is the same as the case of the jj-coupled configuration space. It is found that the structure of sudden change from jj-coupled into LS-coupled configuration spaces through the LS-jj transformation is invariant for Shannon entropy along the isoelectronic sequence. What is more, in an LS-coupled configuration space, there are a large number of information exchanges between energy levels whether with or without strong configuration interaction, and most of the ground and single excited states of Ni-like ions are more suitable to be described by a jj-coupled or other configuration basis set instead of an LS-coupled configuration basis set according to the configuration mixing coefficients and their Shannon entropy. In this sense, Shannon entropy can also be used to measure the applicability of a configuration basis set or the purity of atomic state functions in different coupling schemes.

Inelastic Processes in Nickel–Hydrogen Collisions

Abstract The cross sections and rate coefficients for inelastic processes in low-energy collisions of nickel atoms and positive ions with hydrogen atoms and negative ions are calculated for the collisional energy range 10−4–100 eV and for the temperature range 1000–10,000 K. 74 covalent and three ionic states correlated to 11 molecular symmetries are considered. 3380 partial inelastic processes are treated in total. The study of nickel–hydrogen collisions is performed by the quantum model methods within the Born–Oppenheimer formalism. The electronic structure of the collisional quasimolecule is calculated by the semiempirical asymptotic method for each considered molecular symmetry. For nuclear dynamic calculations the simplified method in combination with the Landau–Zener model is used. Nuclear dynamics within each considered symmetry is treated separately, and the total rate coefficients for each inelastic process have been summed over all symmetries. The largest values of the rate coefficients (exceeding 10−8 cm3 s−1) correspond to the mutual neutralization processes in collisions Ni+(3d 9 2 D) + H−(1s 2 1 S) (the ground ionic state being the initial state), as well as in Ni+(3d 84s 4,2 F) + H−(1s 2 1 S) (the first excited and the second excited ionic states being the initial states) collisions. At the temperature of 6000 K, the rate coefficients with large magnitudes have the values from the ranges (1.35−5.87) × 10−8 cm3 s−1 and (1.02−6.77) × 10−8 cm3 s−1, respectively. The calculated rate coefficients with large and moderate values are important for non–local thermodynamic equilibrium stellar atmosphere modeling.

Mechanism of improving interfacial hydration characteristic of high‐denatured peanut protein induced by cold plasma

AbstractHigh‐denatured peanut protein (HPP), obtained from high‐temperature pressed peanut meal, is limited in the food industry applications due to poor hydration characteristics. The ionic force generated by the cold plasma (CP) was used to activate the surface groups of HPP for generating the interfacial chemical force binding with water molecules, in which the high‐speed shear homogenization (12,000 r/min, 15 min) was as a pretreatment to enhance the accessibility for CP. The content of soluble protein increased from 0.22 ± 0.005 to 1.02 ± 0.03 mg/ml with a CP treatment power of 70 W for 2 min. Meanwhile, CP treatment facilitated the transition of weakly bound water to strongly bound water, therefore, the hydration property was improved. The tertiary, secondary, and apparent structure in HPP stretched after CP treatment. Besides, NH4+ ions in CP excited state improved the flexibility of HPP. Some hydrophilic groups such as COOH, CO, C═O, and OH formed via hydrogen bond to HPP surface was the primary reason for the increased hydration property, which was related to an increase of oxygen on the surface of protein. The increased interfacial hydration property of proteins provides the possibility for the preparation of preparation of functional films, gels, and nutrition agents.Practical applicationsCold plasma (CP), as a nonthermal and surface processing technology, has drawn great attention during the processing. The amount of free radicals, high‐energy electrons, ions, and ultraviolet radiation generated by CP modified the surface structure of the materials, which avoided thermal denaturation and pollution, and had high efficiency. This study indicated that CP treatment enhanced the interfacial hydration characteristic of the high‐denatured peanut protein extracted from peanut meal via analyzing the changes of structure, functional property, as well as chemical bonds, which was beneficial for the preparation of functional films, and gels for drug and nutrition delivery.

Cool white light emission from Dy3+-doped SiO2 – Bi2O3 – Ga2O3 – B2O3 -GeO2- TeO2 glasses: Structural and spectroscopic properties

The authors aim to study multi former oxide glasses doped with different concentrations of Dy3+ (0.00, 0.5, 1.0, 1.5, and 2 mol%) for white light-emitting application. All samples characterized by XRD, FTIR, and optical properties (absorption, excitation, and emission). The optical band gap calculated by a differential method. FTIR spectra confirm the network composed of GaO4, GeO4, TeO4, and BO4 tetrahedra, BO3 triangles, B-O-B linkages, and SiO4 tetrahedra with one NBO. In addition to the TeO3, BiO3, TeO6, and BiO6 vibration groups.Oscillator strengths and Judd–Ofelt parameters (Ω2, Ω4, Ω6) calculated and found that the glass samples had a variable trend from Ω2 > Ω4 > Ω6 to Ω2 > Ω6 > Ω4, at a Dy2O3 content >1 mol%. Furthermore, radiative emission transition probability (AR), branching ratio (βR), and radiative lifetime (τR) estimated for Dy3+ ion in various excited states using J–O parameters. Upon 454 nm excitation, 4F9/2 → 6H15/2 [483 nm (blue)], 4F9/2 → 6H13/2 [575 nm (yellow)], and 4F9/2 → 6H11/2 [680 nm (red)] emission. Among them, it noticed that the transition 4F9/2 → 6H13/2 shows the highest intensity.The CIE chromaticity coordinates, correlated color temperature (CCT), and color purity (CP) indicate a generally neutral white light emission from all samples, which meant their suitability for optical applications. Determination of the white light coordinated from the CIE program, which verifies the values of samples are close to the pure white light. And sample containing 2 mol% Dy3+ close to the standard CIE D65 glow.

Peculiarities and the red shift of Eu2+ luminescence in Gd3+-admixed YAG phosphors

Set of Eu2+-doped (Gd; Y)3Al5O12 (GYAG) powder samples with different Gd/Y ratio was synthesized by inorganic reaction in the solid state from high purity Gd2O3, Y2O3, Al2O3 and EuS. Their structural, scintillation and optical properties were investigated thoroughly by means of X-ray powder diffraction, time-resolved luminescence spectroscopy, photothermal deflection spectroscopy and electron paramagnetic resonance in a broad temperature range to assess the influence of Gd admixture into the YAG host. A phenomenological model was fitted to the measured temperature dependences of the photoluminescence emission spectra and photoluminescence decay times to better understand the dynamics of the 5d excited state of the Eu2+ center. Thermoluminescence and delayed recombination measurements were performed to study the trap distribution and thermally induced ionization of the activator's excited state. Application potential of studied phosphors either in the field of scintillators or solid state white light emitting diode (LED) phosphors is discussed.

Empirical method evaluation of charge – Changing cross sections

A method based on experimental data, theoretical models, and the empirical estimation of experimental parameters in the equilibrium charge distribution of ions is proposed to evaluate charge changing cross sections. This method makes it possible to obtain cross sections for loss and capture of one or several electrons in gaseous and solid targets with the inclusion of the influence of excited states of ions and target atoms.

High-resolution observation of cathode spots in a magnetically steered vacuum arc plasma source

The properties of cathode spots in a magnetically steered vacuum arc plasma source were investigated. The cathode spots were observed with a long-distance microscope coupled to a streak camera, where the entrance slit of the camera was aligned with one of the linear sections of the steered arc source. This is a key feature that allows the observation of spots as they appear along the erosion racetrack. The trends of spot motion and patterns in the emitted light were observed with different sweep times. The streak images were analysed by fast Fourier transformation to check for the presence or absence of characteristic features like characteristic spot lifetimes, since their existence remains a disputed issue. We found that the power spectrum of the arc spot fluctuations does not show any specific frequencies or related times, rather, the spot fluctuations have a broad spectrum following a power law (spectral power density versus frequency), which is indicative for the fractal (self-similar) nature of spot processes. Moreover, we show that—at about 300 MHz under our conditions—we reach the ultimate temporal resolution limit of the method, which is associated with the finite lifetime of excited atomic and ion states. This is a fundamental limit given by the physics of atoms and ions, not a measurement flaw. The temporal resolution limit of about 3 ns also implies a spatial resolution limit of order of a few μm given that radiating species move laterally to the observation direction with at least 103 m s−1.

Observation of rotational coherence in an excited state of CO.

The vacuum ultraviolet (VUV) radiation is generated in the strong-field-ionized CO molecules through 2+1 resonance excitation with two-color femtosecond laser pulses. When scanning the relative delay between two pump pulses, the rotational-resolved VUV radiations show periodic oscillations lasting as long as 500 ps. Fourier analysis reveals that these oscillations correspond to rotational beat frequencies of the A2Πi state of CO+, which is the result of multi-channel interference during the resonant excitation process. High resolution of Fourier transform spectra up to 0.067cm-1 allows us to obtain the fine energy levels of the A2Πi state. The theoretical calculation is in good agreement with the experimental observation. This work reveals the rotational coherence of the ionic excited state and shows the prospect of rotational coherence spectroscopy in measuring fine structures of molecular ions.

Doubly excited states in hot and dense plasmas: Beryllium-like ions for [formula omitted

Effects of the hot and dense plasma on the doubly excited states (DES) of the four-electron beryllium-like ions (BLI) with Z varying from 4 to 10 have been investigated by applying the stabilization method. The Debye–Huckel model has been used to describe the effective potential in the plasma. The four-electron ions are treated as an effective three-body problem by means of the method of model potential. One, four and five DESs lying above the 1s2 2p threshold are found to exist in the ions having Z=4, Z=5 and Z=6−10 respectively. For the plasma-free case our results for the energy and width of the DESs are in agreement with the available results in the literature. A detailed study is made on the changes of energy and width of the DESs of the ions with varying plasma screening strength. Particular emphasis is given to explore the effects of the plasma on the whole sequence of ions.

Synthesis of heptanuclear Ni4Dy3 coordination aggregate using tridentate ligand: X-ray structure, magnetism and theoretical studies

The Schiff base ligand, 2-(((2-hydroxybenzyl)imino)methyl)phenol (H2L) having ONO donor centres are utilized to synthesize {Ni4Dy3} coordination aggregate following the support of six benzoate bridging groups. Sequential addition of Dy(NO3)3·6H2O and NiCl2·6H2O to H2L followed by PhCO2Na completes the coordination driven aggregation of heptanuclear Na[Ni4Dy3(L)4(μ3-OH)4(μ1,1,3,3-PhCO2)2(μ1,3-PhCO2)4(CH3OH)4]∙CH2Cl2·9H2O (1) having 2,3,6M7 − 1 topology. Two adjacent perpendicular inverse Ni2Dy2 partial di-cubane units sharing a common vertex through the central DyIII ion resulted a new structural arrangement within the Ni − Dy family of coordination aggregates. The complex shows no slow magnetic relaxation under zero applied fields and only shows a very weak field dependent magnetization. The DFT calculations revealed weak ferromagnetic exchange between benzoato-bridged NiII ions, whereas the CASSCF calculations were used to identify magnetic anisotropy in NiII and DyIII ions resulting in low-lying excited states of DyIII ions with significant probability for the quantum tunneling of the magnetization, which rationalize the observed fast dynamics in the magnetic properties.

An advanced lifetime measurement method by square wave excitation and lock-in amplifier

Achieving the radiation decay rate with high accuracy is crucial for all light emitters and absorbers. Therefore, a wide variety of measurement approaches have been developed for the measurement of radiation decay rate. Herein, we introduce a method to measure the decay rate with a common photoluminescence intensity setup without any modification. The square wave created by simply turning the output of the laser on and off is used as the excitation waveform, and a lock-in amplifier is used to gather the detected signal, making it a cost-effective way. Moreover, the constructed method can be used in a wide range of frequencies, detection voltages, and lifetimes. Finally, we applied the derived method to measure the photoluminescence lifetime of the first excited state of erbium ions in upconverting erbium-ytterbium silicate samples.

Populations of B2Σu+ and X2Σg+ electronic states of molecular nitrogen ions in air determined by fluorescence measurement

We carry out a combined experimental and numerical investigation on the population distribution between the ground state and the excited state of molecular nitrogen ions in an 800-nm laser field. Efficient population transfers between the ground state ${\mathrm{N}}_{2}^{+}(X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+},\ensuremath{\nu}=0)$ and the excited state ${\mathrm{N}}_{2}^{+}(B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+},{\ensuremath{\nu}}^{\ensuremath{'}}=0)$ occur with a 400-nm time-delayed pulse, resulting in an enhanced fluorescence at 391 and 428 nm. The population distribution between the ground state ${\mathrm{N}}_{2}^{+}(X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+},\ensuremath{\nu}=0)$ and the excited state ${\mathrm{N}}_{2}^{+}(B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+},{\ensuremath{\nu}}^{\ensuremath{'}}=0)$ is extracted from the fluorescence enhancement factor. The results show that the population of ${\mathrm{N}}_{2}^{+}(X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+},\ensuremath{\nu}=0)$ decreases when the laser exceeds 2.1 mJ in our experiment. Our study provides a method to check the population information of both excited and ground states experimentally in a strong-field-induced plasma of ionized nitrogen molecules.

VUV photoprocessing of oxygen-containing polycyclic aromatic hydrocarbons: Threshold photoelectron spectra

Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) have been considered as potential carriers of the 11.3 μm band in interstellar observations. To begin to probe their potential contribution to chemistry in the interstellar medium, we report here threshold photoelectron spectra (TPES) for seven oxygen-containing polycyclic aromatic hydrocarbons 2,3-benzofuran (BF), 2,3-dihydrobenzofuran (DHF), phthalan (PH), dibenzofuran (DBF), dibenzo(B,F)oxepine (DBO), benzo[b]naphtho[2,3-d]furan (BNF) and benzo[b]naphtho[1,2-d]furan (cBNF). Vertical ionization energies to the ground and excited ion states were calculated with the outer-valence Green’s function method, and Franck–Condon simulations, based on harmonic (time-dependent) density functional theory results, were used to explore vibrational excitation upon ionization. CBS-QB3 calculations are also reported. Adiabatic ionization energies (IE) could be measured accurately for five of the molecules: BF (8.35 ± 0.01 eV), PH (8.76 ± 0.01 eV), DBF (8.12 ± 0.02 eV), BNF (7.64 ± 0.02 eV), and cBNF (7.62 ± 0.02 eV). For BF and cBNF, excited state optimizations also allowed Franck–Condon simulations of excited-state bands. The TPES of DHF and DBO feature broad ionization onsets due to large geometry changes upon ionization, as both become planar when an electron is removed. The band maxima yield the vertical IE for these two molecules: 8.2 ± 0.2 eV and 8.0 ± 0.2 eV, respectively, while the best estimate of the adiabatic IE for DHF is 7.98 ± 0.05 eV.

The role of excited electronic states in ambient air ionization by a nanosecond discharge

The mechanism of air ionization by a single nanosecond discharge under atmospheric conditions is studied using numerical simulations. The plasma kinetics are solved with ZDPlasKin and the electron energy distribution function is calculated with BOLSIG+. The model includes the excited electronic states of O and N atoms, which are shown to play the main role in plasma ionization for n e > 1016 cm−3. For electric fields typical in nanosecond discharges, a non-equilibrium plasma (T e > T gas) is formed at ambient conditions and remains partially ionized for about 12 nanoseconds (n e < 1016 cm−3). Then, the discharge abruptly reaches full ionization (n e ≈ 1019 cm−3) and thermalization (T e = T gas ≈ 3 eV) in less than half a nanosecond, as also encountered in experimental studies. This fast ionization process is explained by the electron impact ionization of atomic excited states whereas the fast thermalization is induced by the elastic electron–ion collisions.

Mechanisms of the energy transfer between thulium ions in tungstate and molybdate crystals

In this work, we investigated mechanisms of the energy transfer in Tm : KY(WO4)2, Tm : KLu(WO4)2 and Tm:NaBi(MoO4)2 crystals. Room-temperature absorption and emission spectra were used to determine microparameters of energy migration among thulium ions in the 3H4 and 3F4 excited states in the frames of Förster – Dexter theory. Parameters of cross-relaxation 3H4 + 3H6 → 3F4 + 3F4 and energy migration were obtained via analysis of luminescence decay 3H4 → 3F4 with a hopping model. The parameters describing excitation migration between thulium ions in 3H4 state obtained by two methods were in good agreement. It has been shown that the dipole-dipole mechanism of interaction is responsible for the efficient cross-relaxation process in the crystals under study. The results indicate that the energy migration between 3H4 enhances the cross-relaxation at thulium content more than ∼1.3–1.5 at. % in these laser materials. The obtained values of the migration parameters CDD exceed the values of the cross-relaxation parameters CDA, and the energy transfer in these materials can be described with the hopping model. An efficient cross-relaxation process leads to the relatively high efficiencies of the systems based on these crystals under pumping at 0.8 µm. The dominant process of energy migration between thulium ions in 3F4 excited state makes tungstate and molybdate crystals good candidates for the Ho3+ co-activation for laser generation at 2.1 µm. Parameters obtained in this study can be used for mathematical modeling of laser characteristics.

Rare-Earth-Mediated Optomechanical System in the Reversed Dissipation Regime

Strain-mediated interaction between phonons and telecom photons is demonstrated using excited states of erbium ions embedded in a mechanical resonator. Owing to the extremely long-lived nature of rare-earth ions, the dissipation rate of the optical resonance falls below that of the mechanical one. Thus, a "reversed dissipation regime" is achieved in the optical frequency region. We experimentally demonstrate an optomechanical coupling rate g_{0}=2π×21.7 Hz, and numerically reveal that the interaction causes stimulated excitation of erbium ions. Numerical analyses further indicate the possibility of g_{0} exceeding the dissipation rates of erbium and mechanical systems, thereby leading to single-photon strong coupling. This strain-mediated interaction, moreover, involves the spin degree of freedom, and has a potential to be extended to highly coherent opto-electro-mechanical hybrid systems in the reversed dissipation regime.

Influence Of The Size Of Colloid Nanorized Systems On The Luminescence Intensity Of Eu(III) And Tb(III) Complexes

Optimal conditions for complexation of Tb(III) ions with norfloxacin, keterolac, 2-oxo-4-hydroxyquinoline-3-carboxylic acid amide derivative and Eu(III) with oxytetracycline were established. The dependence of the luminescence intensity (Ilum) of complexes on the acidity of the medium, the type of solvent, the luminescent characteristics of complex compounds were determined, the average lifetime of the excited state of europium and terbium ions in complex compounds in the presence and absence of cationic, anionic and nonionic substances, and the size of colloidal nanoscale systems based on these complexes is established. Analysis of the influence of the type of surfactants on the processes of excitation energy transformation in the complexes of Eu(III), Tb(III) with some drugs was studied by the method of dynamic light scattering. It was found that the luminescence intensity of colloidal nanoscale systems based on Tb(III) and Eu(III) complexes increases in the presence of cationic surfactants(СPC) and nonionic surfactant (Triton X-100), which is associated with a decrease in their size, although other factors may be involved: synergetic effects, displacement of water molecules from the internal coordination sphere of the complex and increasing the rigidity of the complex during coordination with surfactants. Exceptions are Eu – OxTc, Tb-R2, Tb-Nor complexes in the presence of anionic surfactants (SDS), the size of which increases, which can be explained by the formation of triple complexes. The intensity of their luminescence increases, because in these cases there is a displacement of water molecules from the internal coordination sphere of the complex in coordination with SDS.

Collapse of Xe polarized atomic states in magnetic fields

Ionization of two-photon excited states $$5p^{\mathrm {5}}(^{\mathrm {2}}P_{\mathrm {3/2}})6\hbox {p}[^{\mathrm {3}}/_{\mathrm {2}}$$ , $$^{\mathrm {5}}/_{\mathrm {2}}]_{\mathrm {2}}$$ , $$\hbox {M}=2$$ (jl-coupling) of xenon atoms by circularly polarized probe light was studied experimentally in a supersonic beam. The observed photoionization signals revealed oscillation structure due to the Larmor precession of atomic states in an external magnetic field. We derived analytical formulas for the photoelectron current and explained the diversity in the structure of the detected oscillations in terms of the principal lines among multiplet components of optical transitions. The obtained numerical data demonstrate collapse and revival (beating) behavior of the photocurrent due to nonlinearity of Zeeman shifts in the presence of the Paschen–Back effect. Our results indicate the possibility of implementing Doppler-free spectroscopy involving bound-free transitions.