Electron Binding Energies Research Articles

Laser-assisted charge exchange as an atomic yardstick for proton beam energy measurement and phase probe calibration

Laser-assisted charge exchange (LACE) is a novel scheme for injecting ${H}^{\ensuremath{-}}$ ions into proton rings. Lorentz stripping of ${H}^{\ensuremath{-}}$ ions into bare protons in magnetic dipoles is enabled by laser excitation that reduces the electron binding energy. We show that such atomic transitions impose very precise requirements on ion and laser parameters which can be utilized to measure the ion velocity. At the LACE experimental station at the Spallation Neutron Source (SNS), proton beam energy has been measured via LACE to a precision of $<1\text{ }\text{ }\mathrm{MeV}$ for a $\ensuremath{\approx}1\text{ }\text{ }\mathrm{GeV}$ beam. To verify the results against the existing energy measurement method at the SNS which calculates revolution frequency in the accumulator ring, we discuss how knowledge of the beam energy can be employed to synchronize phase probes. Such beam-based calibration using energy measurements via both LACE and the SNS ring show that the two methods produce consistent results.

Gas-Phase Anionic Metal Clusters are Model Systems for Surface Oxidation: Kinetics of the Reactions of Mn- with O2 (M = V, Cr, Co, Ni; n = 1-15).

The reactions of anionic metal clusters Mn- with O2 (M = V (n = 1-15), Cr (n = 1-15), Co (n = 1-12), and Ni (n = 1-14)) are investigated from 300 to 600 K using a selected-ion flow tube. All rate constants show a positive temperature dependence, well described by an Arrhenius equation. Rate constants exceed (or are extrapolated to exceed at higher temperatures) the Langevin-Gioumousis-Stevenson capture rate constant. Application of a capture model accounting for the finite size of the clusters reproduces the size-dependent trends in reactivity. The assumption that reactivity is further controlled by an energetic barrier early in the reaction coordinate is consistent with the experimental observations. An observed correlation of the derived barrier heights on the electron binding energy of Mn- suggests the barrier may be formed at an avoided crossing between electronic states correlating to Mn- + O2 and Mn + O2- reactants, analogous to that previously proposed for Aln- + O2 systems. The mechanism is analogous to that for reactions of O2 with neutral metal surfaces, indicating that gas-phase reactions of anionic metal clusters can be an appropriate model systems for surface oxidation.

Electronically Excited States of Closed-Shell, Cyano-Functionalized Polycyclic Aromatic Hydrocarbon Anions

Few anions exhibit electronically excited states, and, if they do, the one or two possible excitations typically transpire beyond the visible spectrum into the near-infrared. These few, red-shifted electronic absorption features make anions tantalizing candidates as carriers of the diffuse interstellar bands (DIBs), a series of mostly unknown, astronomically ubiquitous absorption features documented for over a century. The recent interstellar detection of benzonitrile implies that cyano-functionalized polycyclic aromatic hydrocarbon (PAH) anions may be present in space. The presently reported quantum chemical work explores the electronic properties of deprotonated benzene, naphthalene, and anthracene anions functionalized with a single cyano group. Both the absorption and emission properties of the electronically excited states are explored. The findings show that the larger anions absorption and emission energies possess both valence and dipole bound excitations in the 450–900 nm range with oscillator strengths for both types of >1×10−4. The valence and dipole bound excited state transitions will produce slightly altered substructure from one another making them appear to originate with different molecules. The known interstellar presence of related molecules, the two differing natures of the excited states for each, and the wavelength range of peaks for these cyano-functionalized PAH anions are coincident with DIB properties. Finally, the methods utilized appear to be able to predict the presence of dipole-bound excited states to within a 1.0 meV window relative to the electron binding energy.

Lanthanum group: Detection and correction of errors in orbital binding energy measurements of internal shells

Experimental data on electronic binding energies in a ground state of lanthanides are analyzed. Internal individual shells K, L, M, N are studied in detail. The data scatter is discussed. Atomic number similarity law of orbital binding energies is shown and deviations from it in some experimental results are treated as measurement errors. Polynomial interpolation of patterns makes it possible to restore missing and correct erroneous data. Comparison is made with experimental data from other sources and theoretical results.

Interfacial Structure Change and Selective Dissolution of Columbite–(Fe) Mineral during HF Acid Leaching

The goal of the paper is to study the charge transfer and reactions at the columbite-(Fe) (FeNb2O6) mineral surface during the HF leaching process. In this paper, X-ray photoelectron spectroscopy (XPS), leaching experiments, and density functional theory (DFT) calculations were used to study the surface element adsorption, charge distribution, chemical state, and energy changes of the mineral surface during the process of leaching columbite–(Fe) with different concentrations of hydrofluoric acid. The results showed that as the concentration of F atoms was increased during the acid leaching process, the Nb–O bond was more likely to be broken than the Fe–O bond; the amount of charge transferred from Nb atom to F atom (0.78 e–0.94 e/atom) was greater than that from Fe atom to the F atom (0.25 e–0.28 e/atom), so it was determined that compared to Fe atoms, it was easier for the Nb atoms to bind to F. The results of XPS analysis showed that the electron binding energies of Nb5+–O, Fe3+–O, and Fe2+–O bonds on the mineral surface increased sequentially, and the M–O bond broke during the acid leaching process, forming more stable M–F bonds. Therefore, the Nb5+–F bonds were easier to form a stable structure. Combined with the ICP results, it was found that in the filtrate after 5M HF and 10M HF acid leaching minerals, c(Nb)/c(Fe) were 2.69 and 2.95, respectively, and the concentration ratio of Nb to Fe element in the mineral was 2 which was lower than 2.69 and 2.95, confirming the result of DFT calculation and illustrating that Nb atoms in columbite-(Fe) mineral were more soluble than Fe atoms.

Electronic properties and hydrogenic impurity binding energy of a new variant quantum dot

In this work, we have studied the electronic states with and without a donor impurity positioned on the first rectangular-shaped surface ( θ = 0°) of the new variant quantum dot (VQD) of azimuthal angle θ , radius R , and height H . The VQD takes several forms depending on the value of the geometric angle θ , which it passes from zero to the limit of 360° to reach the cylindrical form. Within the framework of the effective mass approximation and the limit of the infinite potential, we have obtained the eigenvalues from the Schrödinger equation by using the finite difference method (FDM). The binding energy is calculated after fixing the donor impurity at the center and the eccentric positions of the surface. Indeed, the binding energy takes the clear maximums when the impurity moves vertically and horizontally over the surface. It is very sensitive to each value of the geometric angle, the position of the impurity, the radius, and the height. We think that this new work may reveal important practical interests and provide another way to adjust electronic transitions in optoelectronic devices . • Electronic states and hydrogenic impurity binding energy of a new variant quantum dot is studied. • The effective mass approximation, the infinite potential and the finite difference method are adopted. • The binding energy is obtained after fixing the donor impurity at the center and the eccentric positions of the surface. • The energies depend to the geometric angle, the position of the impurity, the radius, and the height.

Atomic Bonding and Electronic Binding Energy of Two-Dimensional Bi/Li(110) Heterojunctions via BOLS-BB Model.

Combining the bond-order-length-strength (BOLS) and atomic bonding and electronic model (BB model) with density functional theory (DFT) calculations, we studied the atomic bonding and electronic binding energy behavior of Bi atoms adsorbed on the Li(110) surface. We found that the Bi atoms adsorbed on the Li(110) surface form two-dimensional (2D) geometric structures, including letter-, hexagon-, galaxy-, crown-, field-, and cobweb-shaped structures. Thus, we obtained the following quantitative information: (i) the field-shaped structure can be considered the bulk structure; (ii) the field-shaped structure of Bi atom formation has a 5d energy level of 22.727 eV, and in the letter shape structure, this energy is shifted to values greater than 0.342 eV; and (iii) the Bi/Li(110) heterojunction transfers charge from the inner Li atomic layer to the outermost Bi atomic layer. In addition, we analyzed the bonding and electronic dynamics involved in the formation of the Bi/Li(110) heterojunctions using residual density of states. This work provides a theoretical reference for the fine tuning of binding energies and chemical bonding at the interfaces of 2D metallic materials.

Photoelectron Spectra of Gd2O2- and Nonmonotonic Photon-Energy-Dependent Variations in Populations of Close-Lying Neutral States.

Photoelectron spectra of Gd2O2- obtained with photon energies ranging from 2.033 to 3.495 eV exhibit numerous close-lying neutral states with photon-energy-dependent relative intensities. Transitions to these states, which fall within the electron binding energy window of 0.9 and 1.6 eV, are attributed to one- or two-electron transitions to the ground and low-lying excited neutral states. An additional, similar manifold of electronic states is observed in an electron binding energy window of 2.1-2.8 eV, which cannot be assigned to any simple one-electron transitions. This study expands on previous work on the Sm2O- triatomic, which has a more complex electronic structure because of the 4f6 subshell occupancy of each Sm center. Because of the simpler electronic structure from the half-filled 4f7 subshell occupancy in Gd2O2 and Gd2O2-, the numerous close-lying transitions observed in the spectra are better resolved, allowing a more detailed view of the changes in relative intensities of individual transitions with photon energy. With supporting calculations on numerous possible close-lying electronic states, we suggest a potential description of the strong photoelectron-valence electron interactions that may result in the photon-energy-dependent changes in the observed spectra.

Synthesis, characterization, and imaging of radiopaque bismuth beads for image-guided transarterial embolization

Current therapy for hypervascular cancers, e.g., hepatocellular carcinoma, includes occlusion of the tumor blood supply by arterial infusion of embolic microspheres (beads) suspended in iodine-based contrast under fluoroscopic guidance. Available radiopaque, imageable beads use iodine as the radiopacifier and cannot be differentiated from contrast. This study aimed to synthesize and characterize imageable beads using bismuth as the radiopacifier that could be distinguished from iodine contrast based upon the difference in the binding energy of k-shell electrons (k-edge). Radiodense bismuth beads were successfully synthesized some with uniform bismuth distribution across the beads. The beads were spherical and could be infused through clinical microcatheters. The bismuth beads could be imaged with clinical dual-energy computed tomography (CT), where iodine-based contrast could be distinguished from the microspheres. The ability to separate iodine from bismuth may enhance the diagnostic information acquired on follow-up CT, identifying the distribution of the embolic beads separately from the contrast. Furthermore, with sequential use of iodine- and bismuth-based beads, the two radiopaque beads could be spatially distinguished on imaging, which may enable the development of dual drug delivery and dual tracking.

Electronic structure and optical constants of CsPbCl3: The effect of approaches within ab initio calculations in relation to X-ray spectroscopy experiments

We report on experimental and theoretical studies of the electronic structure and optical properties of cesium lead chloride, CsPbCl3. We employ X-ray photoelectron spectroscopy (XPS) to determine binding energies of core-level electrons of as-grown surface of CsPbCl3 crystal and to measure the energy distribution of electronic states in the valence band region. To achieve the best agreement between the shape and energy positions of peculiarities of the XPS valence-band spectrum and the curve of total density of states, we used various approaches treating exchange-correlation potential. In particular, we have realized that the fair agreement is derived when performing calculations within a density functional theory framework using modified Becke-Johnson potential and treating the Hubbard parameter U and spin-orbit coupling. Using possibilities of this technique, we study in detail curves of partial density of states, energy band dispersion, and principal optical constants of CsPbCl3.

Time-resolved pump-probe spectroscopy with spectral domain ghost imaging.

An atomic-level picture of molecular and bulk processes, such as chemical bonding and charge transfer, necessitates an understanding of the dynamical evolution of these systems. On the ultrafast timescales associated with nuclear and electronic motion, the temporal behaviour of a system is often interrogated in a 'pump-probe' scheme. Here, an initial 'pump' pulse triggers dynamics through photoexcitation, and after a carefully controlled delay a 'probe' pulse initiates projection of the instantaneous state of the evolving system onto an informative measurable quantity, such as electron binding energy. In this paper, we apply spectral ghost imaging to a pump-probe time-resolved experiment at an X-ray free-electron laser (XFEL) facility, where the observable is spectral absorption in the X-ray regime. By exploiting the correlation present in the shot-to-shot fluctuations in the incoming X-ray pulses and measured electron kinetic energies, we show that spectral ghost imaging can be applied to time-resolved pump-probe measurements. In the experiment presented, interpretation of the measurement is simplified because spectral ghost imaging separates the overlapping contributions to the photoelectron spectrum from the pump and probe pulse.

Quantum Computational, Spectroscopic, NHO and Molecular Docking Studies on 1-Methyl-nicotinamide (MNA): An Antithrombotic, Anti-inflammatory, Gastroprotective and Vasoprotective Compound

In present work, 1-methylnicotinamide (1-MNA) has been investigated theoretically by density functional theory approach and investigated its vibrational spectroscopy. To complete the structure optimization, determination of vibrational frequencies and other valuable parameters, B3LYP method used with the 6-311++G(d,p) basis set. Atoms in molecules theory (AIM) had been used to evaluate ellipticity, isosurface projection by electron localization function and binding energies. The IR and Raman spectra have also been calculated computationally. NBO analysis employed to determine interactions of donor and acceptor. Fukui functions and molecular electrostatic potential (MEP) showed reactive regions of the molecule. UV-vis spectrum calculated using TD-DFT/PCM methods with different solvents. Thermodynamic properties like free energy, enthalpy and entropy with various temperature were calculated. By the use of the electrophilicity index, the probability of the bioactive nature of the molecule was proved theoretically. Protein-ligand interactions calculated and established by molecular docking. The biological investigations for druglikeness also employed for the (1-MNA).

Оптические сечения поглощения и силы осцилляторов двойного донора магния в кремнии

The optical properties of magnesium impurity in silicon, whose atoms at interstitial positions in the lattice are deep double donors with an ionization energy of 107.56 meV in the neutral state, were studied. For optical transitions from the ground state of a neutral center to the excited levels 2p0 and 2p, the absorption cross sections and oscillator strengths were determined. These parameters were calculated from the impurity absorption spectra that were measured at T  K in samples with different magnesium concentrations. The deep donor content in the samples was determined using Hall effect measurements in the temperature range 78–300 K. The obtained characteristics of intracenter transitions in magnesium were compared with the corresponding literature data for shallow Group V donors in silicon, which are substitutional impurities. It was found that the optical characteristics of the investigated transitions in magnesium are consistent with the dependences of the corresponding parameters on the ionization energy for shallow donors, extrapolated to the region of larger electron binding energies.

Experimental and theoretical study of the effect of bombardment with Ar+ ions on the spectrum of valence electrons of a Si (111) single crystal

The paper studies the effect of disordering of the surface layers on the electronic and optical properties of single-crystal silicon.An analysis of the photoelectron spectra shows that with complete amorphization of the surface density, the condition of Si valence electrons of changes significantly. In particular, the positions of the main maximum of the electrons of the valence band of Si (111) shift by ~ 0.4 eV towards higher binding energies and the band gap Eg increases by 0.1-0.15 eV. The energy of a valence electron in amorphized silicon, which at low impurity concentrations, i.e. at low bombardment doses (D <1015 cm–2), the potential Mkk and, therefore, the shift of the maximum of the density of states vary linearly with respect to concentration. At high impurity concentrations (at doses D> 1015 cm–2), corresponding to the transition to amorphous silicon, the concentration dependence of Mkk is very weak. Therefore, upon amorphization, the peak A of the density of states of the silicon valence band under consideration is shifted to the region of lower electron binding energies. The theoretical substantiation of the obtained experimental results is given.

Comparative research of configuration, stability and electronic properties of cationic and neutral [AuGen]λ and [Gen+1]λ (n=1-13, λ=0, +1) nanoalloy clusters

The configuration, stability, evolution, and electronic properties of neutral and cationic [AuGen]λ and [Gen+1]λ (n=1−13, λ=0, +1) nanoalloy clusters have been systematically investigated by using unbiased global search technique married with double-density functional strategy. The results reveal that although the neutral and cationic global minimal structures of gold-doped germanium clusters differ from each other when n=4, and 6–13, the evolution patterns are consistent. Attaching structures have been changed to Au-encapsulated motif at the turning point of n=11. The analyses of electronic structure and binding energy indicate that doping of an Au atom may decrease the stability of neutral Ge nanoclusters, but can enhance the stability of cationic Ge nanoclusters. The analyses of electronic property show that ionization potentials (IP) of Gen+1 cluster are larger than those of AuGen nanoalloy clusters, indicating that doping of an Au atom can decrease the ionization potential of neutral Ge nanoclusters. The analyses of HOMO and LUMO energy reveal that HOMO-LUMO gaps of neutral AuGen (n=1−13) with the exception of n=2 and 3 are smaller than that of Gen+1 clusters. For cations, the HOMO-LUMO gaps of [AuGen]+ are wider than that of [Gen+1]+ cluster when n=2, 5–7, and 9–11, narrower when n=3, 4, 8 and 13, and nearly identical when n=1 and 12. The PBE-DFT based global descriptors viz. Electronegativity, Hardness, Softness and Electrophilicity Index of [Gen+1]λ and [AuGen]λ (λ=0, +1; n=1−13) nanoclusters are estimated by means of HOMO-LUMO gap. And they possess highly correlation with HOMO-LUMO gap. The agreement between theoretical and experimental results such as IP, binding energy, HOMO-LUMO gap, and bond distance demonstrate the success of the computational analyses in this work.

The role of high-order electron correlation effects in a model system for non-valence correlation-bound anions.

The diffusion Monte Carlo (DMC), auxiliary field quantum Monte Carlo (AFQMC), and equation-of-motion coupled cluster (EOM-CC) methods are used to calculate the electron binding energy (EBE) of the non-valence anion state of a model (H2O)4 cluster. Two geometries are considered, one at which the anion is unbound and the other at which it is bound in the Hartree-Fock (HF) approximation. It is demonstrated that DMC calculations can recover from the use of a HF trial wave function that has collapsed onto a discretized continuum solution, although larger EBEs are obtained when using a trial wave function for the anion that provides a more realistic description of the charge distribution and, hence, of the nodal surface. For the geometry at which the cluster has a non-valence correlation-bound anion, both the inclusion of triples in the EOM-CC method and the inclusion of supplemental diffuse d functions in the basis set are important. DMC calculations with suitable trial wave functions give EBE values in good agreement with our best estimate EOM-CC result. AFQMC using a trial wave function for the anion with a realistic electron density gives a value of the EBE nearly identical to the EOM-CC result when using the same basis set. For the geometry at which the anion is bound in the HF approximation, the inclusion of triple excitations in the EOM-CC calculations is much less important. The best estimate EOM-CC EBE value is in good agreement with the results of DMC calculations with appropriate trial wave functions.

Interrogating the Interplay between Hydrogen and Halogen Bonding in Graphitic Carbon Nitride Building Blocks.

Two graphitic carbon nitride (g-C3N4) molecular building blocks designed for halogen bond driven assembly are evaluated through computational quantum chemistry. Unlike those typically reported in the literature, these g-C3N4-based acceptors each offer three unique sites for halogen bond formation, which when introduced to their donor counterparts, lead to 1:1, 2:1, and 3:1 donor-acceptor complexes. Although halogen bonding interactions are present in all donor-acceptor complexes considered in the work, intermolecular hydrogen bonding emerges in complexes in which an iodine-based donor is directly involved. The halogen bond complexes identified herein feature linear halogen bonds and supportive intermolecular hydrogen bonds that lead to nearly additive electronic binding energies of up to -9.7 (dimers), -18.6 (trimers), and -26.5 kcal mol-1 (tetramers). Select vibrational stretching frequencies (νC-X and νC≡C), and the perturbative shifts they incur upon halogen bond formation, are interrogated and compared to those observed in pyridine- and pyrimidine-based halogen-bonded complexes reported in the literature.

Single crystal growth and the electronic structure of Rb2Na(NO3)3: Experiment and theory

Rb2Na(NO3)3 crystals demonstrate nonlinear optical properties and can be used as a converter of laser radiation in the shortwave region. The crystals were grown in the present work by the Bridgman–Stockbarger method in a ratio of 75 ​wt%(RbNO3) and 25 ​wt%(NaNO3). After the growth, a transparent centimeter size single crystal (6 ​cm long) was obtained for the first time that is very important for its practical application. The unit cell volume of double Rb2Na(NO3)3 nitrate is intermediate between the cell volumes of simple rubidium and sodium nitrates, RbNO3 and NaNO3. Electronic structure of Rb2Na(NO3)3 was studied in the present work from both experimental and theoretical viewpoints. In particular, employing X-ray photoelectron spectroscopy, we have measured binding energies of core electrons and energy distribution of the electronic states within the valence band region of the Rb2Na(NO3)3 crystal and established rather big binding energies for N 1s and O 1s core-level electrons. The bombardment of middle-energy Ar+ ions induces transformation of some nitrogen atoms of the analyzing topmost layers of the Rb2Na(NO3)3 crystal surface from the NO3– group to the NO2– group. To explore in detail the filling of the valence band of Rb2Na(NO3)3 by electronic states associated with constituting atoms, we use first-principles calculations within a density functional theory (DFT) framework. The DFT calculations reveal that O 2p states are the principal contributors to the valence band bringing the main input in its upper portion. The theoretical finding is supported experimentally by fitting the X-ray photoelectron valence band spectrum and the X-ray emission O Kα band on the total energy scale. The conduction band bottom of Rb2Na(NO3)3 is composed by unoccupied O 2p and N 2p states in almost equal proportion.

Surface Properties of Halloysite-Carbon Nanocomposites and Their Application for Adsorption of Paracetamol

Analysis of surface properties of halloysite-carbon nanocomposites and non-modified halloysite was carried out with surface sensitive X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography (IGC). The XPS spectra were measured in a wide range of the electron binding energy (survey spectra) and in the region of C 1s photoelectron peak (narrow scans). The IGC results show the changes of halloysite surface from basic for pure halloysite to acidic for carbon-halloysite nanocomposites. Halloysite-carbon nanocomposites were used as adsorbents of paracetamol from an aqueous solution. The adsorption mechanism was found to follow the pseudo-second-order and intra-particle diffusion models. The Langmuir multi-center adsorption model described well the obtained experimental data. The presence of carbon increased significantly the adsorption ability of halloysite-carbon nanocomposites for paracetamol in comparison to the non-modified halloysite.

Core-Level Excitation Energies of Nucleic Acid Bases Expressed as Orbital Energies of the Kohn-Sham Density Functional Theory with Long-Range Corrected Functionals.

The core electron binding energies (CEBEs) and core-level excitation energies of thymine, adenine, cytosine, and uracil are studied by the Kohn-Sham (KS) method with long-range corrected (LC) functionals. The CEBEs are estimated according to the Koopmans-type theorem for density functional theory. The excitation energies from the core to the valence π* and Rydberg states are calculated as the orbital energy differences between core-level orbitals of a neutral parent/cation and unoccupied π* or Rydberg orbitals of its cation. The model is intuitive, and the spectra can easily be assigned. Core excitation energies from oxygen 1s, nitrogen 1s, and carbon 1s to π* and Rydberg states, and the chemical shifts, agree well with previously reported theoretical and experimental data. The straightforward use of KS orbitals in this scheme carries the advantage that it can be applied efficiently to large systems such as biomolecules and nanomaterials.