Excited Ions Research Articles

Lightning impulse breakdown behavior of natural ester and modified natural ester under long oil gap: An experiment and first-principles simulation analysis

The investigation of lightning impulse (LI) breakdown characteristics in long oil gaps with insulating liquids is of utmost importance for the design of high-voltage, large-capacity transformers. This study focuses on analyzing the negative LI breakdown characteristics of two types of insulating oils, namely high viscosity natural ester soybean oil (SO) and low viscosity modified natural ester palm fatty acid ester (PFAE), under long oil gap conditions. The research includes testing and analyzing the voltage and current waveforms, LI breakdown voltage, and streamer discharge development speed of these liquids across oil gaps ranging from 25 mm to 105 mm. The findings demonstrate that the breakdown voltage of both insulating oils tends to increase as the oil gap distance widens. At a 25 mm gap, the average breakdown voltage of PFAE is not significantly different from that of SO. However, at a 105 mm gap, the average breakdown voltage of PFAE surpasses that of SO by 46.29%. Weibull distribution analysis is applied to the LI breakdown voltage data of the two insulating liquids, resulting in empirical formulas for breakdown voltage as a function of oil gap width at failure probabilities of 1%, 50%, and 90%. The discharge development rate of PFAE is lower than that of SO, especially in the oil gap of 105 mm. With the increase of the oil gap, the streamer development rate of the two insulating oils showed a trend of increasing. Using density functional theory based on first principles, the study investigates changes and discrepancies in parameters such as ionization potential, electron affinity, softness, excitation energy, and molecular surface electrostatic potential of the two insulating liquids with varying electric field strengths. The atomic and molecular scale analysis reveals the primary factors contributing to the contrasting macroscopic lightning shock breakdown characteristics of SO and PFAE. The comprehensive combination of experimental and simulation results suggests that PFAE exhibits greater potential for implementation in high-voltage, large-capacity transformers compared to SO. This study aims to bridge the gap in knowledge regarding the LI breakdown characteristics of different natural esters in long oil gaps. The experimental and theoretical findings presented in this paper provide a foundation for the practical application of natural esters and modified natural esters in high-voltage and large-capacity transformers.

Investigation on plasma ionization process of a micro-cathode arc thruster

Micro-cathode arc thrusters (μCATs) are space propulsion options suitable for microspacecraft, and have recently attracted much attention because of their low electrical power requirements and simple, compact propellant systems. The plasma ionization process, however, is not currently well understood. In this study, a μCAT prototype was designed with the use of different specific materials for each component, enabling the study of the ionization process from the emissive light of excited and ionized states from different elements. ICCD emission spectroscopy and scanning monochromator measurements are conducted inside the electrode channel of a μCAT with a coaxial configuration. The excited state atomic spectral results and ionization state spectral results give us a comprehensive understanding of the behavior of neutral particles and ions during the discharge process of the μCAT. The ionization sequence follows in the order of C+, Al+, Ti+, Cu+, and Ti2+. From the duration of the spectral lines, C I has the shortest duration (16.9 μs), which shows that the ablation of the conductive film is mainly concentrated during the first half of the discharge, while anode and cathode ionization occur over the entire discharge duration. Additionally, Al+ ionization is observed during the discharge process, showing that part of the discharge energy is expended in ionizing the thruster outer shell, resulting in efficiency loss. An ionization ratio of k is proposed in this work to represent the relative ionization of the conductive film and cathode material, aiding us in determining the optimal operation conditions for lifetime extension.

The effect of ancillary ligands on hydrocarbon C-H bond functionalization by uranyl photocatalysts.

The aqueous uranyl dication has long been known to facilitate the UV light-induced decomposition of aqueous VOCs (volatile organic compounds), via the long-lived highly efficient, uranyl excited state. The lower-energy visible light excited uranyl ion is also able to cleave unactivated hydrocarbon C-H bonds, yet the development of this reactivity into controlled and catalytic C-H bond functionalization is still in its infancy, with almost all studies still focused on uranyl nitrate as the precatalyst. Here, hydrocarbon-soluble uranyl nitrate and chloride complexes supported by substituted phenanthroline (Ph2phen) ligands are compared to each other, and to the parent salts, as photocatalysts for the functionalization of cyclooctane by H atom abstraction. Analysis of the absorption and emission spectra, and emission lifetimes of Ph2phen-coordinated uranyl complexes demonstrate the utility of the ligand in light absorption in the photocatalysis, which is related to the energy and kinetic decay profile of the uranyl photoexcited state. Density functional theory computational analysis of the C-H activation steps in the reaction show how a set of dispersion forces between the hydrocarbon substrate and the Ph2phen ligand provide control over the H atom abstraction, and provide predictions of selectivity of H atom abstraction by the uranyl oxo of the ring C-H over the ethyl C-H in an ethylcyclohexane substrate.

Excited state iminium form can explain the unexpected solvatochromic behavior of symmetric 1,5- and 1,8-diaminonaphthalenes.

A new model, based on the presence of the excited state iminium ion (Ar = NH2+), is proposed to interpret the solvatochromic behavior of symmetric 1,5- and 1,8-diaminonaphtahelenes (DANs) in aprotic to protic media. The importance of using explicit solvent models during DFT calculations in protic solvents to find the proper excited structure for symmetric molecules is also highlighted.

Electron transport characteristics in water under electrostrictive effect

The transport characteristics of electrons are crucial for the initiation and development of pulse discharge in water. In this work, we develop a physical model of electron transport that consides elastic and inelastic collision cross sections. The purpose of this study is to investigate frequency variations of elastic collisions, ionization and excitation collisions with different initial electron energy values, and to explore the characteristic of electron energy loss in water. The Monte Carlo method is employed to track structure characteristics of electron transmission and scattering under varying energy values. The results show that the electrons of lower energy (~20 eV) are significantly impacted by the water molecule scattering, hence their transmission capacities are weakened. When the incident energy of electron reaches 100 eV, the scattering deviation distance is roughly equivalent to the transmission depth, about 6–8 nm, and the maximum deviation angle <i>θ</i><sub>shift</sub> ~ 60°. When the electron incident energy is in a range of 10–1000 eV, the number of elastic collisions is much greater than the number of excitation and ionization collisions, and the number of ionization collisions and excitation collisions increases significantly with the increase of electron energy. The higher the electron incident energy, the greater the energy loss is. However, the energy loss decreases sharply with the extension of penetration distance. For the ionization collision, the average ionization energy loss, <i>W</i>, decreases rapidly with the increase of electron energy, and ultimately maintains at a level of 20–30 eV, which is consistent with the experimental results reported.

Potential-Assisted Target Atomic Ionization Excitation Radiation Near-Infrared Spectra

Potential-Assisted Target Atomic Ionization Excitation Radiation Near-Infrared Spectra

Doppler imaging of a southern ApSi star HD 152564

ABSTRACT We present the results of the spectroscopic study of a chemically peculiar star HD 152564. Using medium-resolution (R = 37 000) observations obtained with the high-resolution fibre échelle spectrograph mounted on the South African Large Telescope, we determined atmospheric parameters Teff = 11 950 ± 200 K and log g = 3.6 ± 0.2 dex. Abundance analysis revealed mild deficiency of the light elements and an overabundance of up to ∼2 dex of metals, with the greatest excess for silicon. With these characteristics, HD 152564 is a typical member of the silicon subgroup of Ap stars. The rotational modulation of the light curve and line profiles of HD 152564 are typical for the inhomogeneous surface distribution of elements in its atmosphere. We performed multi-element Doppler imaging of the surface of HD 152564. Abundance maps constructed for He, O, Mg, Si, and Fe revealed the concentration of these elements in a sequence of equatorial spots as well as in the circumpolar rings. The photometric maximum of the light curve coincided with the visibility of two most overabundant silicon spots. Abundances determined from the different ionization stages of Fe and Si show clear evidence for vertical stratification of these elements in the atmosphere of HD 152564. Meanwhile, the horizontal distribution of silicon reconstructed from the lines of different ionization stages and excitation energies appears to be identical with increasing average abundance deeper in atmosphere.

ON THE FORMATION OF EXCITED YTTRIUM PARTICLES UNDER ION BOMBARDMENT OF YTTRIUM AND YTTRIUM ALUMINUM GARNET

Emission spectra of excited yttrium particles ejected from the surface of the yttrium metal and yttrium aluminum garnet (YAG) at Ar+ ions are studied. The efficiency of yttrium particles excitation defined from experimental data. The assumption is made that the difference in the excitation efficiency for yttrium atoms and ions is due to the different contribution of processes of formation of the excited atoms or ions ejected from solids at the ion bombardment of garnet and metal.

Broadening of the power deposition profile in on-axis X2 ECRH experiments in the L-2M stellarator and the low-threshold parametric decay instability of the pump wave

The effect of considerable broadening of the power deposition profile in on-axis X2 electron cyclotron resonance heating experiments observed in the L-2M stellarator is interpreted in the paper as one of the consequences of the low-threshold parametric decay instability of the pump wave, resulting in excitation of ion and electron Bernstein daughter waves. The instability is considered under the specific L-2M experimental conditions and shown to be absolute. The threshold of this instability is exceeded in the experiment. This finally allows explaining, at least qualitatively, the effect of nonlocal microwave power deposition detected in L-2M.

Single-Bubble Sonoluminescence of Colloidal Suspensions of Europium(II) Salt Nanoparticles.

Colloidal suspensions of EuCl2, EuBr2, and EuSO4 nanoparticles (<50 nm) in dodecane and EuSO4 in 70% H2SO4 were synthesized. Moving single-bubble sonoluminescence (m-SBSL) spectra were obtained for a bubble performing radial oscillations in these suspensions and translational motions at the antinode of a standing ultrasonic wave with a frequency of about 27 kHz. In these spectra (at a spectral resolution of 10 nm), the sono-excited luminescence bands of the Eu2+ ion were detected for the first time, coinciding in the shape and position of the maxima (404, 413, and 377 nm for EuCl2, EuBr2, and EuSO4, respectively) with the bands of Eu2+ located in a crystalline environment in the photoluminescence spectra of nanoparticles of europium salts in suspensions. The detected sonoluminescence of Eu2+ arises due to the injection of nanoparticles into a bubble deformed during motion and excitation of a lanthanide ion at the periphery of the bubble volume during collisions of nanoparticles with charged particles, mainly electrons, coming from a hot nonequilibrium plasma, which periodically arises during bubble compression. Evidence for the excitation of the europium ion in the bubble is the absence of its luminescence bands in the SBSL spectra of the translationally immobile bubble, in which nanoparticles are unlikely to enter. The nanoparticles that enter the bubble also undergo decomposition in the plasma into fragments, in particular, with the formation of Eu, Eu+ in the excited state. The atomic lines of these fragments were recorded for the first time in the m-SBSL spectrum with a resolution of 1 nm for a suspension of EuSO4 nanoparticles in 70% H2SO4. The resulting m-SBSL spectra will add to the library of characteristic spectra of objects of sonoluminescent spectroscopic analysis and will make it possible to identify and determine the content of Eu or Eu2+ in these objects.

Transient Non-Collinear Magnetic State for All-Optical Magnetization Switching.

Resonant absorption of a photon by bound electrons in a solid can promote an electron to another orbital state or transfer it to a neighboring atomic site. Such a transition in a magnetically ordered material could affect the magnetic order. While this process is an obvious road map for optical control of magnetization, experimental demonstration of such a process remains challenging. Exciting a significant fraction of magnetic ions requires a very intense incoming light beam, as orbital resonances are often weak compared to above-band-gap excitations. In the latter case, a sizeable reduction of the magnetization occurs as the absorbed energy increases the spin temperature, masking the non-thermal optical effects. Here, using ultrafast X-ray spectroscopy, this work is able to resolve changes in the magnetization state induced by resonant absorption of infrared photons in Co-doped yttrium iron garnet, with negligible thermal effects. This work finds that the optical excitation of the Co ions affects the two distinct magnetic Fe sublattices differently, resulting in a transient non-collinear magnetic state. The present results indicate that the all-optical magnetization switching (AOS) most likely occurs due to the creation of a transient, non-collinear magnetic state followed by coherent spin rotations of the Fe moments.

Study of Electron Impact Excitation of Na-like Kr Ion for Impurity Seeding Experiment in Large Helical Device

In this work, a krypton gas impurity seeding experiment was conducted in a Large Helical Device. Emission lines from the Na-like Kr ion in the extreme ultraviolet wavelength region, such as 22.00 nm, 17.89 nm, 16.51 nm, 15.99 nm, and 14.08 nm, respective to 2p63p(2P1/2o)−2p63s(2S1/2), 2p63p(2P3/2o)−2p63s(2S1/2), 2p63d(2D3/2)−2p63p(2P3/2o), 2p63d(2D5/2)−2p63p(2P3/2o), and 2p63d(2D3/2)−2p63p(2P1/2o) transitions, are observed. In order to generate a theoretical synthetic spectrum, an extensive calculation concerning the excitation of the Kr25+ ion through electron impact was performed for the development of a suitable plasma model. For this, the relativistic multiconfiguration Dirac–Hartree–Fock method was employed along with its extension to the relativistic configuration interaction method to compute the relativistic bound-state wave functions and excitation energies of the fine structure levels using the General Relativistic Atomic Structure Package-2018. In addition, another set of calculations was carried out utilizing the relativistic many-body perturbation theory and relativistic configuration interaction methods integrated within the Flexible Atomic Code. To investigate the reliability of our findings, the results of excitation energies, transition probabilities, and weighted oscillator strengths of different dipole-allowed transitions obtained from these different methods are presented and compared with the available data. Further, the detailed electron impact excitation cross-sections and their respective rate coefficients are obtained for various fine structure resolved transitions using the fully relativistic distorted wave method. Rate coefficients, calculated using the Flexible Atomic Code for population and de-population kinetic processes, are integrated into the collisional-radiative plasma model to generate a theoretical spectrum. Further, the emission lines observed from the Kr25+ ion in the impurity seeding experiment were compared with the present plasma model spectrum, demonstrating a noteworthy overall agreement between the measurement and the theoretical synthetic spectrum.

Hybrid simulation of the plasma characteristics in a dual‐frequency dual‐antenna inductively coupled plasma discharge

AbstractDual‐frequency (DF) dual‐antenna inductively coupled plasma (ICP) sources have been proposed as one of the methods to produce large‐area uniform plasma. In this study, a hybrid model, consisting of a fluid module and an electron Monte Carlo (eMC) module, is used to further investigate the modulation of the plasma characteristics (i.e., induced electric field, electron energy distribution, electron heating mechanism, electron temperature, and plasma density) by the low‐frequency (LF) and high‐frequency (HF) currents in a DF argon discharge. When the inner LF current increases from 12 to 22 A at a fixed outer HF current of 10 A, the induced electric field is strengthened near the LF coil and weakened near the HF coil. The fraction of high‐energy electrons at different spatial positions increases with the increase of LF current, which is caused by the sufficient collision heating in the skin layer of LF source, leading to an increase in electron temperature. When the outer HF current rises from 7 to 13 A with the inner LF current fixed at 17 A, the induced electric field is enhanced near the HF coil and weakened near the LF coil. The fraction of low‐energy electrons at different positions increases with the increase of HF current since the energetic electrons from the skin layer of HF source are cooled due to the ionization, excitation, and stepwise ionization collisions between electrons and neutral particles, as well as the weakened induced electric field near the LF coil. As a result, the electron temperature drops with the increase of HF current. Moreover, when the LF and HF currents increase, the plasma density increases, and the distribution of plasma density is also significantly modulated.

Dipole and quadrupole resonance excitation in linear quadrupoles.

In the development of commercial quadrupole mass spectrometers, there is an interest in improving the performance characteristics such as transmission, resolution, and mass range. In particular, parametric and dipolar resonance excitation of trapping ions are used for linear quadrupole mass filters. Theoretical methods and numerical simulation of ion trajectories were applied for study of ion-optical properties. The review is devoted to description of different excitation methods to improve QMF performance and consists of three parts. The first part presents the results of a linear ion trap simulation for various operating conditions and excitation methods. The second part considers the effects of dipole excitation (DE) on the performance of the quadrupole mass filter. The last part analyzes the formation of stability islands by different methods of quadrupole excitation. To date conditions of mass separation in quadrupole mass filters with sin wave supply were described for stability islands of the first and third stability regions formed by quadrupole and DE. By complicating the electronics such methods allow to overcome the destructive influence of electric field distortions and obtain a resolving power and ion transmission efficiency comparable with commercial devices. At quadrupole resonance excitation by a two-frequency signal, it is possible to reduce the length of electrodes three times without losses in resolution and transmission, which reduces the cost of rod set production with micrometer accuracy. Dipole resonance excitation allows controlling the shape of the mass peak by changing amplitude and phase of the auxiliary AC signal. The main factors affecting the resolving power of a linear ion trap are described theoretically. The numerical modeling results are confirmed by experiment.

Nonsequential double ionization channels control of CO2 molecules with counter-rotating two-color circularly polarized laser field by laser wavelength

Abstract Using the classical ensemble model, we investigate the effect of laser wavelength on the electron dynamics process of nonsequential double ionization (NSDI) for linear triatomic molecules driven by a counter-rotating two-color circularly polarized laser field. Based on the delay time between recollision and final double ionization, two particular ionization channels are separated: recollision-impact ionization (RII) and recollision-induced excitation with subsequent ionization (RESI). Numerical results show that with the increase of the laser wavelength, the triangle structure of the ion momentum distribution becomes more obvious, which indicates that the electron–electron correlation of NSDI is enhanced. In addition, we find that the ratio of the RESI channel gradually decreases with the increase of the laser wavelength, while the ratio of the RII channel is opposite. However, the dominant channel is still RESI. It means that the two ionization channels can be controlled effectively by changing the laser wavelength.

Atomic scale microparameter analysis of modified natural ester molecules related to impulse discharge characteristics under electric field

Modified natural ester (MNE) has significant potential for application in transformers as an environmentally friendly and renewable energy source. In comparison to natural esters, MNE offers notable advantages in terms of viscosity and power frequency breakdown voltage. However, the lightning impulse breakdown characteristics of MNE and the atomic-scale microscopic mechanisms related to its discharge characteristics remain unclear. Understanding the lightning impulse breakdown characteristics of MNE is crucial for ensuring the safe operation of transformers. In this paper, the density functional theory is used to calculate the change law of the microscopic parameters related to the discharge characteristics of MNE under the electric field under the action of electric field, so as to theoretically evaluate the lightning impulse discharge behavior of MNE. The results reveal that the electronic and geometric structures of MNE molecules are influenced by electric fields, which is the primary factor contributing to the variations in microscopic parameters under different electric field strengths. As the electric field intensity increases, the dipole moment of MNE tends to increase, while the ionization potential and excitation energy of MNE tend to decrease. The decrease of ionization potential, excitation energy and energy gap of MNE molecules is about 6.61%–68.01%, 4.34%–47.66% and 2.01%–69.23%. By comparing the calculated results of mineral oil, natural ester, and MNE microparameters, it can be inferred that the lightning impulse breakdown behavior of MNE is similar to that of natural ester and lightning impulse breakdown voltage of MNE is higher than that of natural ester but still lower than that of mineral oil. The average negative polarity lightning impulse voltages of MNE, natural ester and mineral oil in the 85 mm oil gap are about 245 kV, 199 kV and 304 kV, respectively. The test results confirmed the simulation conclusions. This study provides robust theoretical support for understanding the lightning impulse breakdown characteristics of MNE and ensuring its safe operation in transformers.

A systematic improvement to UGA-SSMRCCSD equations and its implication for potential energy curves.

The Unitary Group Adaptation (UGA) offers a very compact and efficient spin adaptation strategy for any spin-free Hamiltonian in a many body framework. Our use of UGA in the context of state-specific (SS) Jeziorski-Monkhorst Ansatz based multireference coupled cluster (MRCC) theory obviates the non-commutativity between the spin-free cluster operators via a normal ordered exponential parametrization in the wave operator. A previous formulation of UGA-SSMRCC by us [R. Maitra, D. Sinha, and D. Mukherjee, J. Chem. Phys. 137, 024105 (2012)], using the same ansatz, employed certain sufficiency conditions to reach the final working equations, which cannot be improved systematically. In this article, we will present a more rigorous formulation that follows from an exact factorization of the unlinked terms of the Bloch equation, resulting in equations on which a hierarchy of approximations can be systematically performed on the emergent additional terms. This derivation was shown in our recent article [D. Chakravarti, S. Sen, and D. Mukherjee, Mol. Phys. 119, e1979676 (2021)] in the context of a single open shell CC formalism and was applied to spectroscopic energy differences where the contribution of the new terms was found to be of the order of ∼0.001eV for ionization potential, electron affinity, and excitation energy. In the current work, we will present a comparison between the earlier and current formulations via both a theoretical analysis and a numerical demonstration of the dramatic effect of the additional terms brought in by the factorization on potential energy curves. The contribution of such terms was found to gain importance with an increase in the number of singly occupied active orbitals in the model space functions.

Highly‐Doped Lanthanide‐Based Nanocrystals with Cooperative Core‐Shell Upconversion Emission for Multicomponent One‐Pot Chemical Transformations

AbstractIn order to apply near infrared (NIR) light‐activated upconversion nanocrystals (UCNCs) in photochemistry, extremely bright luminescence is needed to excite the ultraviolet (UV)‐visible light absorbing photocatalyst/substrate. In this study, a multilayered UCNC consisting of a β‐NaYF4:Yb0.2, Tm0.005 core, heavily Yb3+‐doped β‐NaYbF4:Y0.09, Tm0.01 intermediate shell, and inert β‐NaYF4 outer shell is prepared. By compartmentalizing the sensitizer (Yb3+)‐activator (Tm3+) pair in the core and intermediate shell with different concentration ratios, a cooperative luminescence effect is discovered. Apart from core emission, energy harvesting followed by sequential energy transfer from a high density of neighboring Yb3+ to Tm3+ in the intermediate shell induces a large population of excited emitter ions. Furthermore, after back energy transfer from the core to intermediate shell, the energy is not quenched by intrinsic trap sites but is instead transferred to Tm3+, further boosting emission in the UV, blue, and NIR regions. The exceptionally bright UCNC is then used to drive NIR‐light‐activated one‐pot multicomponent reactions involving the upconversion energy transfer from UCNC to UV‐visible light absorbing photocatalyst/substrate, Lewis acid catalytic activity of the lanthanide ions (Y3+) on the surface, and photothermal property of the UCNC. The reactions studied include the deacetalization‐Knoevenagel condensation reaction, photooxidation‐cyanation reaction, and hydrodehalogenation‐cyanosilylation reaction.

Generation of Ultrafast Attosecond Magnetic Field from Ne Dimer in Circularly Polarized Laser Pulses

By numerically solving time-dependent Schrödinger equations, we investigate the generation of electron currents, ultrafast magnetic fields and photoelectron momentum distributions (PMD) when circularly polarized laser pulses interact with a Ne dimer in the charge migration (CM) process. By adjusting the laser wavelength, we consider two cases: (i) coherent resonance excitation (λ = 76 nm) and (ii) direct ionization (λ = 38 nm). The results show that the current and magnetic field generated by the Ne dimer under resonance excitation are stronger than under direct ionization. This phenomenon is due to the quantum interference between the initial state 2pσ g and the excited state 3sσ g under resonance excitation, so the CM efficiency of the dimer can be improved and the strength of the PMD under different ionization conditions is opposite to the strength of the electron current and induced magnetic field. In addition, we also find that both 2pπ g and 2pπ u have coherent resonance excitation with 3sσ g state and generate periodic oscillating currents for the Ne dimer. The study of the dynamics of the Ne dimer under different ionization conditions lays a foundation for research of ultrafast magnetism in complex molecular systems.

Simulation of double resonant excitation of ions in an asymmetric linear ion trap mass analyzer.

Improving the analytical performance of linear ion traps (LITs) is crucial for the advancement of high-performance LIT mass spectrometers. In this study, a double resonant excitation method was employed in an asymmetric LIT to achieve high ion unidirectional ejection efficiency and enhanced mass resolution. The asymmetric trapping field was generated by stretching one x electrode with a distance α. The double resonant excitation was achieved by applying an alternating voltage out of phase and a supplementary alternating voltage in phase to the x and y electrode pairs of the LIT, respectively. Numerical simulations of ion trajectories were performed to validate the effectiveness of this method. The mass resolution of the asymmetric LIT with double resonant excitation could be improved to ~3800, which was over two times compared to that with only dipolar resonant excitation, while both reached ~90% in ion unidirectional ejection efficiency. By employing the double resonant excitation method, the mass resolution could be improved significantly in the asymmetric LIT, while maintaining a considerably high ion unidirectional ejection efficiency. This method might provide a general solution for enhancing ion detection efficiency and mass resolution of LIT mass spectrometers.