Electron-ion Energy Research Articles

Precision spectroscopy of dielectronic recombination experiments for highly charged ions at large facility HIAF: a simulation study

Dielectronic recombination (DR) experiments of highly charged ions not only provide essential atomic benchmark data for astrophysical and fusion plasma research but also serve as a stringent test for strong-field quantum electrodynamics (QED) effects, relativistic effects, and electron correlation effects. High-Intensity Heavy-Ion Accelerator Facility (HIAF), currently under construction at Huizhou, China, has a high-precision spectrometer ring (SRing) equipped with a 450 kV electron-cooler and an 80 kV ultracold electron-target. This advanced setup facilitates precise measurements of the DR process for highly charged ions across a broad range of center-of-mass energies, from meV to tens of keV. In this study, we employ molecular dynamics methods to simulate the electron beam temperature distribution of the ultracold electron-target at the SRing. The simulation results indicate that, following the designed adiabatic magnetic field and acceleration field treatment, the transverse and longitudinal electron beam temperature from the thermionic electron gun can be reduced from 100 meV to below 5 meV and 0.1 meV, respectively. Furthermore, we analyze the impact of this ultracold electron beam temperature on the resonance peaks and energy resolution in DR experiments. The resolution gain at the SRing electron-target is particularly pronounced at small electron-ion collision energies, which provides unique experimental conditions for the DR experiments. Using lithium-like ${ }_{54}^{129} \mathrm{Xe}^{51+}$ and ${ }_{92}^{238} U^{89+}$ ions as examples, we simulate the DR resonance spectrum at the SRing and compare them with the simulated results from the experimental cooler storage ring CSRe. The results reveal that the SRing experiments can resolve fine DR resonance structures with ultra-high energy resolution compared to those from the CSRe. This work lays the foundation for precise DR spectroscopy of highly charged ions at the SRing to stringent test of the strong-field QED effects and extract nuclear structure information.

Comparative study of electron temperature and ion energy in two different magnetic nozzle thruster designs

Conventional ion thruster technologies face challenges such as electrode and grid erosion and the need for additional neutralizer devices. In this article, we discuss two thruster concepts that achieve plasma acceleration by means of a magnetic nozzle, and thus avoid the need of a neutralizer device. The concept of a magnetic nozzle converting the thermal energy available in the electrons movement to ion kinetic energy is a well accepted model in the community. We discuss a novel thruster concept based on electrode-less electron cyclotron resonance plasma generation via a slot antenna design. The geometry of this thruster concept results in a converging-diverging character of the magnetic field topology along the plume direction. To this date it is not known in which way this new thruster design influences the electron dynamics and thus the ion energy. To understand the correlation between ion energy and electron temperature of this thruster system, it is compared with a well-known thruster prototype operating on similar principles, however, realizing microwave coupling and magnetic field topology in a different way. Both thruster designs operate within comparable power, frequency, and volume flow ranges. The ion energy with maximum probability is measured for both thrusters using a retarding potential analyzer in the same vacuum environment. Additionally, the electron temperature is measured with a Langmuir probe for various operation points of the thrusters, differing in input power level, volume flow, set excitation frequency, and argon or xenon as propellant.

Chemical space-informed machine learning models for rapid predictions of x-ray photoelectron spectra of organic molecules

Abstract We present machine learning models based on kernel-ridge regression for predicting X-ray photoelectron spec- tra of organic molecules originating from the ionization energies of 1s electrons in carbon (C), nitrogen (N), oxygen (O), and fluorine (F) atoms. We constructed training dataset through high-throughput calculations of core-electron binding energies (CEBEs) for 12,880 small organic molecules in the bigQM7ω dataset, employing the ∆-SCF formalism coupled with meta-GGA-DFT and a variationally converged basis set. The models are cost-effective, as they require the atomic coordinates of a molecule generated using universal force fields while estimating the target-level CEBEs corresponding to DFT-level equilibrium geometry. We explore transfer learning by utilizing the atomic environment feature vectors learned using a graph neural network framework in kernel-ridge regression. Additionally, we enhance accuracy using the ∆-machine learning framework by leveraging inexpensive baseline spectra derived from Kohn–Sham eigenvalues. Upon application to 208 com- binatorially substituted uracil molecules, larger than those in the training set, our analyses reveal that while the models may not yield quantitatively accurate predictions of CEBEs on a molecule-by-molecule basis, they do exhibit a strong linear correlation, which proves valuable for virtual high-throughput screening purposes. We present the dataset and models as the Python module, cebeconf, to facilitate further explorations.

Band Diagram Insights into the Kinetic and Thermodynamic Engineering of Tandem Photocatalytic Cells.

In this work, we theoretically investigate the impact of kinetic and thermodynamic properties on the performance of photocatalytic cells operating in an unassisted tandem configuration, including electron affinity and ionization energies, recombination rates, and reaction rates. To this end, we present general rules and metrics for identifying and isolating the origin of an observed shift in the onset potential at either the photoanode or the photocathode of these devices. The correlation between kinetic and thermodynamic shifts in the onset potential is demonstrated through the use of band diagrams and key comparable features within readily accessible characterization tools: current-voltage plots are taken both under illumination and in the dark and further coupled with Mott-Schottky plots. To illustrate this conceptual framework, a model system comprised of a p-type doped BiVO4 photocathode and an n-type doped BiVO4 photoanode is employed. By varying each of the aforementioned kinetic and thermodynamic parameters in isolation, the manner in which these various mechanisms shift the onset potential is demonstrated. This work intends to showcase how kinetic and thermodynamic effects are distinctly manifested in these commonly used characterization tools and further proposes thermodynamic band-edge engineering as a potentially useful and largely unexplored avenue for possibly improving tandem cell performance, in addition to the conventional approach of optimizing kinetics.

Electron-ion relaxation times in 1–100 eV warm dense aluminum and gold

We calculated the electron-ion energy relaxation times in warm dense aluminum and gold. Our calculations span a wide temperature range from a thousand to a million kelvins for both dense aluminum and gold. To determine the temporal evolution of electron and ion temperatures, we employed the two-temperature model with the SESAME equation-of-state tables, and well-known electron-ion coupling factors. Our calculations indicate that the relaxation times for warm dense aluminum were within 5 ps, whereas they were within 20 ps for warm dense gold. The maximum relaxation times were observed at initial electron temperatures of approximately 30,000 K for both aluminum and gold. Our calculated relaxation times using the SESAME database agree very well with the existing theories both in the cold-solid and hot-plasma limits. Furthermore, we found that the melting times calculated using the Lindemann criterion were in good agreement with the melting times for gold from measurements in recent literature.

DFT studies on N-(1-(2-bromobenzoyl)-4-cyano-1H-pyrazol-5-yl)

In this work, molecular descriptors of N-(1-(2-bromobenzoyl)-4-cyano-1H-pyrazol-5-yl) halogenated benzamides (1a-h) have been computed using a quantum chemical technique through DFT. Prior work involved the synthesis of compounds (1a-h) and the assessment of their anticancer activity on breast, colon, and liver tumors: MCF-7, HCT-116, and HepG-2 cell lines respectively. Since 1a, 1b, and 1d showed the most potential anticancer impact, their ability to inhibit EGFRWT was investigated. Based on the biological data, 1b inhibited EGFRWT the most. According to the docking evaluation, an H-bond with the threonine residue was one of the main non-covalent contacts between 1b and the EGFRWT active site residues. PES, MESP, HOMOs, LUMOs, energy band gap, global reactivity indices [electron affinity (A), ionization energies (I), electrophilicity index (ω), nucleophilicity index (ε), chemical potential (μ), electronegativity (χ), hardness (η), and softness (S)], condensed Fukui functions, NBO, and NCIs are the molecular descriptors of 1a-h that were computed using DFT technique. According to the theoretical investigation results, compounds (1a-h) might have anticancer effects; these findings are consistent with the biological findings from our previous research. Compound 1b had the lowest binding energy, according to an assessment of the binding energies between the threonine and the three most active compounds (1a, 1b, and 1d). This is consistent with the outcomes of the docking study and the biological examination of the influence of 1a, 1b, and 1d on EGFRWT.

Correlation of Electron Configuration, Electronegativity, and Ionization Energy of Strontium on the Modification of Eutectic Si in High-Pressure Die Cast A380 Al–Si Alloys

Correlation of Electron Configuration, Electronegativity, and Ionization Energy of Strontium on the Modification of Eutectic Si in High-Pressure Die Cast A380 Al–Si Alloys

Core performance predictions in projected SPARC first-campaign plasmas with nonlinear CGYRO

This work characterizes the core transport physics of SPARC early-campaign plasmas using the PORTALS-CGYRO framework. Empirical modeling of SPARC plasmas with L-mode confinement indicates an ample window of breakeven (Q > 1) without the need of H-mode operation. Extensive modeling of multi-channel (electron energy, ion energy, and electron particle) flux-matched conditions with the nonlinear CGYRO code for turbulent transport coupled to the macroscopic plasma evolution using PORTALS reveals that the maximum fusion performance to be attained will be highly dependent on the near-edge pressure. Stiff core transport conditions are found, particularly when fusion gain approaches unity, and predicted density peaking is found to be in line with empirical databases of particle source-free H-modes. Impurity optimization is identified as a potential avenue to increase fusion performance while enabling core-edge integration. Extensive validation of the quasilinear TGLF model builds confidence in reduced-model predictions. The implications of projecting L-mode performance to high-performance and burning-plasma devices is discussed, together with the importance of predicting edge conditions.

Study of the frontier molecular orbitals of an acceptor molecule system: BTP-4F-T2C8, BTP-4F-T2EH, and BTP-4F-T3EH

Non-Fullerene-Acceptors (NFA’s) are a type of acceptor molecules widely used for the manufacture of organic solar cells (OSC). Due to its benefits and advantages over its Fullerene-Acceptors (FA) counterparts, these have become the point of interest in the field of organic photovoltaic technology. In the present theoretical study, electron structure calculations were performed on the frontier molecular orbitals (FMO) of a system of acceptor molecules used in the synthesis of organic solar cells called: BTP-4F-T2C8, BTP-4F-T2EH and BTP-4F-T3EH. The results demonstrate a good trend and approach to the LUMO orbitals of each NFA. With the above it was possible to calculate other parameters such as electron affinities and ionization energies, demonstrating that the electronic structure of the BTP-4F-T3EH gives it a greater accepting capacity. In addition, absorption spectra were successfully obtained, whose maximum wavelengths closely match the highest peaks of the experimental spectrum. This demonstrates that the selection of the method used can successfully replicate other optical aspects.

Ion kinetic effects on the formation of intense laser-driven shock waves

The ion kinetic effect on the formation of intense laser-driven collisional shock waves is investigated via hybrid fluid-particle-in-cell simulations. It is found that the ion heat flux dominates the shock formation, which is considerably larger than the electron heat flux in the shock region. The rise of the temperature due to the laser energy deposition drives a heatwave into the overdense plasma, creating an electron–ion energy exchange zone between the critical surface and heat wave front. The heated ions, which are generated at the electron–ion energy exchange zone via the friction force, are found to travel to the high-density region and cause a tail distribution gain. Despite the small quantity, the heated tail ions contribute most of the ion heat flux during the shock formation. Additionally, as the electron heat flux decreases, the population of the heated tail ions is reduced, leading to a fall in the ion heat flux. This results in the delay or even suppression of the shock formation, because the ions are in a non-equilibrium state in the vicinity of the shock region, the ratio of the downstream ion temperature to the upstream ion temperature tends to a modestly decrease in comparison to the theory. The study provides a clear picture of the formation process of laser-driven shock waves.

Electron emission from deep traps in HfO2 under thermal and optical excitation

The ratio between the energies of optical and thermal ionization depends on the defect nature and the strength of the interaction of trapped electrons with phonons. Knowing this ratio for a certain type of defect allows one to predict, e.g., thermal emission energies from the optically measured values. We present the results of direct empirical extraction of the ratio between optical and thermal electron emission energies for HfO2 bulk electron traps combined with theoretical analysis of the physical mechanism of electron transitions from the trapped state to the mobility edge. We show that, by applying different excitation mechanisms, we affect the same deep traps inside the HfO2 band gap; i.e., these traps are both optically and thermally active and are likely to have similar nature. The extracted empirical optical/thermal ionization energy ratio of 2.2±0.3 is in good agreement with the polaronic nature of the probed electron traps, as shown by the results of theoretical calculations. Our results provide experimental and theoretical methodologies for consistently linking thermal and optical ionization energies of electron traps and describing their distributions in the band gap of amorphous oxides, and can help improve modeling frameworks for reliability issues related to oxide traps. Published by the American Physical Society 2024

DFT computation of the electron spectra of thiophene

Recent experiments on thiophene using synchrotron radiation stimulated the present density functional theory (DFT) study of the various types of electron spectroscopy using the DFT methods we developed in our laboratory. Besides the confirmation of the experimental interpretations, the results of the present study strongly validate the methods used for the various types of electron spectroscopy. The average absolute deviations of the DFT results for thiophene from experiment are 0.22 eV for vertical ionization energies of outer valence electrons, 0.10 eV for carbon 1s binding energies, 0.19 eV for vertical valence excitation energies, and 0.18 eV for X-ray absorption energies. The calculated carbon 1s binding energies for bithiophene and terthiophene are also within 0.1 eV of synchrotron experiment. We conclude that workers using synchrotron radiation to study electronic processes of gas-phase molecules can apply our DFT methods for the interpretation of their experimental results.

Stability and Reactivity of Aromatic Radical Anions in Solution with Relevance to Birch Reduction.

We investigate the electronic structure of aromatic radical anions in the solution phase employing a combination of liquid-jet (LJ) photoelectron (PE) spectroscopy measurements and electronic structure calculations. By using recently developed protocols, we accurately determine the vertical ionization energies of valence electrons of both the solvent and the solute molecules. In particular, we first characterize the pure solvent of tetrahydrofuran (THF) by LJ-PE measurements in conjunction with ab initio molecular dynamics simulations and G0W0 calculations. Next, we determine the electronic structure of neutral naphthalene (Np) and benzophenone (Bp) as well as their radical anion counterparts Np- and Bp- in THF. Wherever feasible, we performed orbital assignments of the measured PE features of the aromatic radical anions, with comparisons to UV-vis absorption spectra of the corresponding neutral molecules being instrumental in rationalizing the assignments. Analysis of the electronic structure differences between the neutral species and their anionic counterparts provides understanding of the primarily electrostatic stabilization of the radical anions in solution. Finally, we obtain a very good agreement of the reduction potentials extracted from the present LJ-PES measurements of Np- and Bp- in THF with previous electrochemical data from cyclic voltammetry measurements. In this context, we discuss how the choice of solvent holds significant implications for optimizing conditions for the Birch reduction process, wherein aromatic radical anions play crucial roles as reactive intermediates.

Molecular Orbital Properties and Insulation Characteristics of Flaxseed Oil

This study aims to analyze the molecular orbital parameters of flaxseed oil (linum usitatissimum) and to measure the AC breakdown voltages at different electrode gaps with various rate of rises. AC breakdown voltages of flaxseed oil are measured at 1.0 and 2.5 mm electrode settings with 0.5 kV/s, 2.0 kV/s and 3.0 kV/s rate of rises, adhering to IEC and IEEE standards. UV-VIS (Ultraviolet–Visible) and FT-IR (Fourier Transform-Infrared) measurement tests carried out after breakdown voltage measurements reveals that the molecular structure of the oil remains stable against electrical discharges. The compounds of flaxseed oil are analyzed using GC-MS and it is determined that the oil mainly consists of seven triglycerides in accordance with the literature. In order to better understand the electrical behavior of these triglycerides, molecular orbital properties such as ionization potential, electron affinity and electron energy gap are analyzed employing Density Functional Theory (DFT) using B3LYP/6-311 + G(d,p) and B3PW91/6-311 + G(d,p) basis sets. The advantages of flaxseed oil such as AC dielectric strength, stability against breakdown mechanism, homogeneous molecular electrical characteristics of its compounds and antioxidant content make this oil as one of the potential natural ester alternatives to mineral oils in the power system industry.

Ab-initio and density functional theory (DFT) computational study of the effect of fluorine on the electronic, optical, thermodynamic, hole and electron transport properties of the circumanthracene molecule

In this paper, a systematic study of the electronic, optical, thermodynamic, optoelectronic, and nonlinear optical properties with RHF, B3LYP, wB97XD and BPBE methods using the cc-pVDZ basis set have been described to investigate the influence of fluorine (F) atom, which is an electron donor, on the circumanthracene (C40H16). Global reactivity descriptors, hole and electron transport properties were also calculated and compared with other studies on the same molecule. DFT/B3LYP results show that the undoped C40H16 molecule (Egap = 2.135 eV) and its fluorine-doped derivatives (C40F16 and C40H10F6) are semiconducting materials. However, doping the C40H16 molecule with the fluorine atom, partially or totally, favors the creation of a strong donor-acceptor system by considerably reducing its energy gap (Egap). The energy gap values of molecules doped using DFT/B3LYP method are 2.020 eV and 2.081 eV for the C40F16 and C40H10F6 molecules, respectively. These gap energies are below 3 eV, which favours the electronic properties of these molecules. They can be used to design organic solar cells. The nonlinear optical parameters were calculated and compared with those of urea. The values of βmol and μ calculated for C40F16 and C40H10F6 are higher than those of urea; this shows that these two materials have good nonlinear optical properties and therefore, are very good candidates for the design of optoelectronics and photonics devices. Futhermore, our results show that the perfluorination effect on the circumanthracene molecule increases the hole and electron reorganization energies, the vertical and adiabatic electron affinities and ionization energies, the optoelectronic and nonlinear optical properties, the transition excitation energy and the reactivity indices. The reorganization energies values suggest that these materials have promising transport properties. The natural bond orbital (NBO) analysis was also performed to determine the stability energy and charge delocalization in molecules. The theoretical results of the compounds studied in our work are in agreement with the experimental results. This confirms their molecular structures.

Biological and theoretical investigation of cyclohexylamine dithiocarbamate metal (II) complexes

AbstractA series of metal (II) complexes of N‐cyclohexyl amine dithiocarbamate ligand are synthesized and characterized by Fourier transform infrared, 1H, 13C NMR, mass spectroscopy, and elemental analysis. The surface structural pattern of the prepared complexes were investigated by scanning electron microscope and X‐ray diffraction techniques. The prepared complexes possessed crystalline characteristic with size average ranging from 16 to 30 nm. Moreover, the biological activity of the synthesized complexes were tested against Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus. Among the prepared complexes, copper (II) complex displayed the highest activity. In addition, molecular docking study was performed against bacterial tyrosinase enzyme which showed good binding interactions and is in agreement with the experimental findings. Furthermore, the in silico toxicity studies reveal that the complexes are mostly non‐irritant with mild toxicity. Different quantum parameters including electron affinity, ionization energy, dipole moment, hardness and vibrational frequencies were calculated for the ligand and its complexes using Gaussian 09 program and B3LYP/SDD level of theory.

Hammett correlation in competition experiments in dissociation of ionised substituted benzophenones and dibenzylideneacetones.

A convenient method of applying competition experiments to devise a Hammett correlation in the dissociation by α-cleavage of 17 ionised 3- and 4-substituted benzophenones, YC6H4COC6H5 [Y=F, Cl, Br, CH3, CH3O, NH2, CF3, OH, NO2, CN and N(CH3)2] is reported and discussed. The results given by this approach, which rely on the relative abundance of [M-C6H5]+ and [M-C6H4Y]+ ions in the electron ionisation spectra of the substituted benzophenones, are compared with those obtained by previous methods. Various refinements of the method are considered, including reducing the ionising electron energy, making allowance for the relative abundance of ions such as C6H5+ and C6H4Y+, which may be formed to some extent by secondary fragmentation, and using substituent constants other than the standard σ constants. The reaction constant, ρ, of 1.08, which is in good agreement with that deduced previously, is consistent with a considerable reduction in electron density (corresponding to an increase in positive charge) at the carbon of the carbonyl group during fragmentation. This method has been successfully extended to the corresponding cleavage of 12 ionised substituted dibenzylideneacetones, YC6H4CH=CHCOCH=CHC6H5 (Y=F, Cl, CH3, OCH3, CF3, and NO2), which may fragment to form either a substituted cinnamoyl cation, [YC6H4CH=CHCO]+, or the cinnamoyl cation, [C6H5CH=CHCO]+. The derived ρ value of 0.76 indicates that the substituent, Y, influences the stability of the cinnamoyl cation somewhat less strongly than it does the analogous benzoyl cation.

Predictive JET current ramp-up modelling using QuaLiKiz-neural-network

This work applies the coupled JINTRAC and QuaLiKiz-neural-network (QLKNN) model on the ohmic current ramp-up phase of a JET D discharge. The chosen scenario exhibits a hollow profile attributed to core impurity accumulation, which is observed to worsen with the increasing fuel ion mass from D to T. A dynamic D simulation was validated, evolving j, , , , n Be, n Ni, and n W for 7.25 s along with self-consistent equilibrium calculations, and was consequently extended to simulate a pure T plasma in a predict-first exercise. The light impurity (Be) accounted for Z eff while the heavy impurities (Ni, W) accounted for P rad. This study reveals the role of transport on the hollowing, which originates from the isotope effect on the electron-ion energy exchange affecting . This exercise successfully affirmed isotopic trends from previous H experiments and provided engineering targets used to recreate the D q-profile in T experiments, demonstrating the potential of neural network surrogates for fast routine analysis and discharge design. However, discrepancies were found between the impurity transport behaviour of QuaLiKiz and QLKNN, which lead to notable hollowing differences. Further investigation into the turbulent component of heavy impurity transport is recommended.

Energetic and Electronic Properties of NpH0/+/– and PuH0/+/–

High-level correlated molecular orbital theory calculations have been performed to predict the thermodynamic and electronic properties of diatomic NpH0/+/- and PuH0/+/-. The excited states up to ∼10,000 cm-1 were predicted for these molecules at the multireference SO-CASPT2 level. The inclusion of spin-orbit effects is fundamental to predict the low-lying state ordering. NpH is predicted to have a 5Π0 ground state, and PuH has a 6Π1/2 ground state at the SO-CASPT2 level. The adiabatic electron affinities (AEAs) and ionization energies (IEs) of NpH and PuH were calculated to be 0.389 and 6.156 and 0.396 and 6.296 eV, respectively, using the Feller-Peterson-Dixon approach. The AEA increases going from AcH (0.425 eV) to ThH (0.820 eV) and decreases from ThH to PuH. The IEs of Pa-Np hydrides are close to ∼6.2 eV followed by an increase of 0.14 eV to PuH (6.296 eV). The An-H bond dissociation energy (BDE) decreases from 276.4 (AcH) to 107.1 (PuH) kJ/mol; the BDE(NpH) is ∼80 kJ/mol higher than that of PuH. Natural bond orbital calculations show that the bond character for these molecules is mainly ionic, An+H-. The additional electron in NpH- and PuH- populates the 6d orbital, and NpH+ and PuH+ are formed by the removal of a 7s electron. The current work in conjunction with prior work on the AcH to UH in different charge states provides insights into how these properties change across the actinide series.

Asymmetrical ignition of radio frequency discharge in atmospheric pressure cascade glow discharges

A two-dimensional self-consistent fluid model was developed to investigate the ignition of radio frequency (RF) discharge in an atmospheric helium cascade glow discharge. In particular, the model considers the case where a pulsed discharge is excited ahead of the RF discharge by applying pulsed DC voltage and RF voltage to two parallel plate electrodes separately. The spatio-temporal distribution of electron, ion, electric field, and mean electron energy demonstrate that the electron and ion localize in the vicinity of RF electrode with the extinguishment of pulsed discharge, whereas a sheath region formed above the pulsed electrode due to the space charge. It explains the experimental findings of asymmetric ignition of RF discharge in the interelectrode gap. With the migration of ion towards the pulsed electrode, the RF discharge achieves the stable operation. Furthermore, the migration time of ion from the RF electrode to pulsed electrode is estimated to be 3.0 μs, which is consistent with the calculated migration time of ions across the discharge gap.