3P Atoms Research Articles

Nitride‐Bridged Mo‐Fe‐S Double‐Cubanes: Syntheses, Redox Behaviors and Comparison with their W Analogs

The FeMo cofactor (FeMoco) of the Mo‐dependent nitrogenase was identified as a Mo‐Fe‐S cluster incorporating a 2p atom in the core. The edge‐bridged double‐cubane (EBDC, [M2Fe6(µ3‐S)6(µ4‐S)2]z (M = Mo/V; z denotes charge)) clusters were demonstrated to undergo rearrangement reactions to generate the apex‐fused double‐cubane clusters ([M2Fe6(μ2‐S)2(μ3‐S)6(μ6‐S)]z) as mimics of the PN‐clusters. The introduction of 2p atoms into the core of EBDC clusters will furnish the possibility of mimicking the FeMoco structure through rearrangement. In this work, an EBDC Mo‐Fe‐S cluster with core nitrides, namely [(Tp*)2Mo2Fe6(μ4‐N)2S6Cl4]2− (Tp* = tris(3,5‐dimethyl‐1‐pyrazolyl)hydroborate), has been synthesized. Subsequent terminal ligand substitution has produced a series of EBDC clusters with isostructural cores. Further studies of the series of nitride‐containing EBDC clusters are focused on their structures and redox properties, as well as comparisons with their W analogs. The results indicate that the core structures of these clusters are affected by distinct hetero‐metal centers and different terminal ligands to a limited extent, but the redox behavior and redox potentials of these clusters differ significantly. This work provides us with a viable method for regulating the properties of the nitride‐containing EBDC clusters, which may be enlightening for further studies of the rearrangement reactions towards mimicking the FeMoco structure.

Significant Isotope Effects from the Nonadiabatic Couplings in the Cl(2P) + HD(v = 0, j = 0) Reaction.

The impact of non-Born-Oppenheimer couplings on the isotopic effects in the reaction of the Cl(2P) atom with the HD (v = 0, j = 0) molecule is investigated with our recently developed nonadiabatic time-independent quantum scattering methods, where the full open-shell characteristics are included in the six-state model, and also with the recently developed two-state model solving by time-independent methods, where part of the open-shell characteristic is included. The same reaction is also calculated with the simple adiabatic model using the lowest adiabatic potential energy surface. Compared with the results from different models, it is found that the reactivity of the Cl + HD → HCl + D channel is significantly overestimated in the adiabatic model. In contrast, the reactivity of the other channel agrees well with the nonadiabatic models. This is due to the van der Waals well in the reactant channel being changed a lot by including the nonadiabatic couplings. These quantum dynamics calculations suggest that sometimes the adiabatic model should be used with caution; otherwise, it may result in significant deviations for some reactions.

S-type heterojunction enhance the photocatalytic activity of TiO2/AgBr/Ag using loofah sponge as template towards ciprofloxacin degradation

Photocatalyst TiO2/AgBr/Ag (TBA) composites using loofah sponge as a template were successfully prepared for the first time. The photocatalytic activities of the TBA composites were evaluated by removing ciprofloxacin (CIP) under visible light. The PDOS shows that the valence band edge of TBA-30 is primarily composed of Ti 3d atom states, with small contributions from O 2p atom states. The conduction band edge is dominated by Ag 4d and O 2p atom states, with minor contributions from Br 4p atom states. TBA-30 composites demonstrate outstanding photocatalytic performance, degrading 87% of the target within 180 min. The degradation rate of CIP decreased to 70.19% after five runs, Furthermore, the TOC removal efficiency of CIP reached 84.2% in the end. CIP intermediates and degradation pathway were determined by GC-MS. Three-dimensional excitation-emission matrix fluorescence spectra (3D EEM) were used to study the degradation of CIP molecules. Trapping experiments and electron paramagnetic resonance (EPR) characterisation identified superoxide (·O2-) and photogenerated holes (h+) as the primary active radicals. Furthermore, formed S-type heterojunction and Ag as the electron capture site enhanced the separation efficiency of photoinduced electron-hole pairs. The DFT calculation was used to study the electron transport performance of TBA-30 by calculating the charge density difference.

First-principle calculations to investigate electronic and optical properties of carbon-doped silicon

Silicon (Si) is a highly promising candidate for the applications of photovoltaics. However, the bandgap constraints, low conductivity, and bounded photon energy absorption make the applications restricted. Herein, we investigated the optimized structural, electronics and optical characteristics of carbon (C) doped Si by first-principle calculations. The analysis of the various doping illustrates that doping of the C atom in Si adds extra stability by reducing the Si–Si bond length from 2.3 Å to 2.002 Å Si–C bond length which leads to the shrinkage of lattice parameters. In addition, the bandgap of Si is reduced from 1.13 eV to 0.2 eV if a 14.28 % C-doping is employed. As the C-doping is reduced to 6.66 %, the bandgap increases to 0.87 eV with a transition from indirect to direct bandgap. Further reduction in C-doping varies the bandgap from 0.87 eV to 1.13 eV. The density of states calculations show that for a low C-doping, the transitions are mainly due to Si-3p and Si-3s orbitals in the valence band which leads to a higher energy level, while for higher C-doping, the C atom 2p orbital contribution causes a reduction in bandgap and addition of stability in the doped structures. The conductivity of the Si can be increased by utilizing higher C-doping which reduces hole effective mass by 46 % and electron effective mass by 24 %. Optical absorption of Si can be enhanced at a higher spectral range while adopting a higher C-doping, which shifts the absorption peak shapes from spikes to flat and extends to 7 eV photon energy.

First-Principles Insights into the Acetic Acid Sensing Capability of the C<sub>39</sub>N Armchair Nanotube

In this paper, (5,5) single-walled carbon nanotube was doped by substitutional nitrogen (N) atom forming bridgehead C-N bonds in the resulting C39N armchair nanotube. It was then interacted with acetic acid to investigate its detection capability using first-principles calculations in the context of Density Functional Theory (DFT). As known, DFT is a very efficient and accurate method in calculating the properties of the atoms and molecules, and their interactions. Accordingly, the O-H bond of the acid has not undergone a heterolytic dissociation caused by the weak interaction of the materials. In the valence region of the C39N-acid, the O atoms (2p) are the main causes of additional states as shown in the projected density of states (pDOS). Calculations of the charge density difference revealed the occurrence of charge redistribution and nonuniform charge transfer between the acid and the sidewalls of the C39N. Further topological investigation of the system revealed no localized electrons between the interaction points indicating a physical binding mechanism. These electronic responses have shown the biosensing ability of C39N to detect and capture acetic acid.

Nonadiabatic dynamics in a forest of coupled states: Electronic state branching in the VUV photodissociation of N2.

Multi-state electronic dynamics at higher excitation energies is needed for the understanding of a variety of energy rich situations, including chemistry under extreme conditions, vacuum ultraviolet (VUV) induced astrochemistry, and attochemistry. It calls for an understanding of three stages, energy acquisition, dynamical propagation, and disposal. It is typically not possible to identify a basis of uncoupled quantum states that is sufficient for the three stages. The handicap is the large number of coupled quantum states that is needed to describe the system. Progress in quantum chemistry provides the necessary background to the energetics and the coupling. Progress in quantum dynamics takes this as input for the propagation in time. Right now, it seems that we have come of age with potential detailed applications. We here report a demonstration to a coupled electron-nuclear quantum dynamics through a maze of 47 electronic states and with attention to the order in perturbation theory that is indicated using propensity rules for couplings. Close agreement with experimental results for the VUV photodissociation of 14N2 and its isotopomer 14N15N is achieved. We pay special attention to the coupling between two dissociative continua and an optically accessible bound domain. The computations reproduce and interpret the non-monotonic branching between the two exit channels producing N(2D) and N(2P) atoms as a function of excitation energy and its variation with the mass.

Charge transfer and ionization cross-sections in collisions of singly charged lithium ions with helium and nitrogen atoms

We present a non-perturbative classical treatment of the charge transfer and ionization processes in collisions between singly charged lithium ions with helium and nitrogen atomic targets. Single capture and single ionization total cross sections are calculated using a three-body classical trajectory Monte Carlo (CTMC) method in which the interaction between the collision partners is described by a Garvey-type model potential. The cross sections are evaluated for collision energies between 20 keV and 100 MeV. In particular, we found excellent agreement between our results and the available experimental data for the case of the single capture of He(1s) by Li+ ions. In addition, our CTMC results are in a reasonable agreement with the experimental results for collision energies higher than 200 keV for single capture of N(2p) atoms by Li+. Furthermore, we present single ionization cross sections for both collision systems.

Collision integrals for N(4S)–N(4S), N(4S)–N(2D), and N(4S)–N(2P) interactions

Collision integrals for the scattering of nitrogen (N) atoms are essential to model transport properties of air plasmas, which can be highly dependent on the species involved. At high temperatures, N atoms may exist in their excited states. Therefore, collision integrals for N atoms are computed at the temperature range of 500–50 000 K, in which the interactions between the excited [N(2D) and N(2P)] atoms and ground N(4S) atom are considered. The interaction between the excited N(2P) atom and ground N(4S) atom is considered for the first time. A comparison of the collision integrals from our combined-hyperbolic-inverse-power-representation (CHIPR) potential energy function with those obtained using other analytical potential energy functions in the literature is given. The results show that the trend of potential energy curves (PECs) in dissociated asymptotic and short-range regions has an important effect on the collision integrals. These regions are difficult to cover in experiments. Here we seek the state-of-the-art ab initio methods for a theoretical guideline to compute the PECs of N2, which are then modeled by the CHIPR function. PECs of some low-lying states are also refined by available experimental spectroscopic data. Overall, our collision integrals are reliable.

Electronic Structure Calculations with the Exact Pseudopotential and Interpolating Wavelet Basis

Electronic structure calculations are mostly carried out with Coulomb potential singularity adapted basis sets such as STO or contracted GTO. With another basis or for heavy elements, the pseudopotentials may appear as a practical alternative. Here, we introduce the exact pseudopotential (EPP) to remove the Coulomb singularity and test it for orbitals of small atoms with the interpolating wavelet basis set. We apply EPP to the Galerkin method with a basis set consisting of Deslauriers–Dubuc scaling functions on the half-infinite real interval. We demonstrate the EPP–Galerkin method by computing the hydrogen atom 1s, 2s, and 2p orbitals and helium atom configurations He1s2, He1s2s1S, and He1s2s3S. We compare the method to the ordinary interpolating wavelet Galerkin method (OIW–Galerkin), handling the singularity at the nucleus by excluding the scaling function located at the origin from the basis. We also compare the performance of our approach to that of finite-difference approach, which is another practical method for spherical atoms. We find the accuracy of the EPP–Galerkin method to be better than both of the above-mentioned methods.

Cubane-type tungsten-iron-sulfur clusters with a nitrogen atom in the core: terminal ligand substitutions and redox behaviors.

The lack of M-Fe-S (M = Mo or W) clusters incorporating a second period (2p) atom in the core has resulted in limited investigations and poor understanding of the physical and chemical properties of the M-Fe-S clusters closely related to the FeMo cofactor. In this work, systematic studies have been carried out to explore the chemical reactivities at the terminal ligand sites and the redox properties of a series of clusters comprising a [WFe3S3N] cubane core, based on the previously developed cluster [(Tp*)WFe3S3(μ3-NSiMe3)Cl3]1-. Substitutions of the terminal chlorides with ethanethiolate, methanethiolate, thiophenolate, p-thiocresolate and azide occurred smoothly, while the replacement of the chlorides with carbene ligands required the reduction of the precursor into [(Tp*)WFe3S3(μ3-NSiMe3)Cl3]2- first. The reduced cluster core could also be supported by thiophenolates as terminal ligands, but not thiolates or azides. It is remarkable that the thiophenolate ligated reduced cluster can be synthesized from the precursor [(Tp*)WFe3S3(μ3-NSiMe3)Cl3]1-via different synthetic routes, either reduction followed by substitution or substitution followed by reduction, either in situ or stepwise. This work indicates that terminal ligands contribute significantly to determine the chemical and physical properties of the clusters, even though they might affect the cluster core to a limited extent from a structural point of view, which raises the possibility of delicate control in regulating the physical/chemical properties of M-Fe-S clusters with a heteroleptic core incorporating 2p atom(s).

Effect of alloying elements on the interface of fcc-Fe/Ni3Al by first principle calculations

The effect of alloying element segregation on the interface properties of the fcc-Fe/Ni3Al was investigated using the first-principles approach based on density functional theory, revealing the element segregation mechanisms from the perspectives of atoms and electrons. The results show that the alloying elements tend to replace position 1 on the interface of fcc-Fe phase side, and the order of stability after replacement is Ti, Nb, Mo, Cr and Mn. The state density diagrams show that the 4d orbital electrons of Mo and Nb contribute to increase the peak of Al atom 2p orbital at −5 eV, while the 3d orbital electrons of Cr and Ti tend to weaken the peak of Fe atom 3d orbital at 1 eV. The degrees of electron cloud enrichment and consumption increase between interface atoms of the difference charge diagrams indicate that the bonding strength increases and the interface stability is improved. The result of bond population is consistent with the differential charge density diagram. The study has a certain guiding significance for interfacial segregation behavior of alloying elements in heat-resistant steels.

Half-metallic magnetism in triazines g-C4N3and g-C3N4tailored with H, Li, and 2p elements

The graphitic carbon nitride g-C4N3, since its experimental realisation, and particularly being proven a free - standing monolayer with half - metallic ferromagnetism, has drawn growing research interest in spintronics. Here, the author presents a study using density functional calculations, on the electronic structure and magnetic ordering of g-C4N3 and its sister monolayer triazine g-C3N4, tailored with H, Li, and 2p elements. Half-metallic ferromagnetism of pristine g-C4N3 is first elucidated with an emphasis on its localised spin magnetic moments due to pyridinic N-sp2 electrons. The author then proposes various scenarios tailoring the structure of these two materials, in order to induce itinerant magnetism therein, towards greater potential applications in spintronics. The key to that problem lies in the chemistry of H, Li, and other 2p atoms at the graphitic N or C and vacant sites of our crystal lattices. Interestingly, in certain elaborate scenarios involving pairs of 2p adatoms at the latter, the author have obtained new half-metallic material structures where both localised and itinerant magnetism mechanisms coexisted. This result is explained in a clear physicochemical picture where the effect of spin - charge transfer shapes the electronic structures of these new monolayers.

Ionization of H(2p) atom by 30 keV proton and antiproton impact

Ionization process of the hydrogen atom, being initially in the excited 2p-state, projected by 30 keV proton and antiproton impact has been investigated. The second-Born approximation (SBA) is used to measure the triple differential cross sections (TDCSs). The closure relation is employed on the second-Born term to come over consideration of the intermediate states. The triple differential cross-sections are represented graphically against the ejection angle, for two scattering angles and ejected energies into both scattering and perpendicular geometric planes. The single differential cross-section (SDCS) is calculated in the framework of the first-Born approximation.

Investigation of N(4S) kinetics during the transients of a strongly emissive pulsed ECR plasma using ns-TALIF

A nanosecond-two-photon absorption laser-induced fluorescence (ns-TALIF) technique was employed to investigate the transients of a strongly emissive, pulsed microwave discharge. We analysed the conditions that have to be fulfilled in order to use the TALIF intensities measured with the laser central frequency tuned to the absorption peak instead of the fully integrated laser excitation spectrum absorption for measuring N-atom densities. We demonstrated the validity of the method under our conditions and applied it to the straightforward monitoring of N-atom densities during the transients of a pulsed ECR plasma. In particular, we demonstrated the existence of an unexpected increase in N(4S) atom density of about 10% at the early stage of the transition from high- to low-power phase. Using a self-consistent, quasi-homogenous plasma model encompassing a detailed state-to-state kinetics, a thorough analysis of the N-atom and N2(B) kinetics was carried out and enabled this enhancement to be attributed to surface de-excitation of N(2D) and N(2P) atoms. The rise of the N(4S) atom density can serve as an indicator of the concentration of N(2D) and N(2P) atoms in the discharge.

Theoretical Investigation on Structural and Magnetic Properties of Mn-doped and C co-doped Zn12Se12 Nanoclusters

Background: Mn doped ZnSe low dimensional materials are attractive for different biological labels, gene silencing and dilute-magnetic device. ZnSe clusters are one of the basic building blocks of quantum dots and even cluster-assembled nanodevices, stable structures of undoped ZnSe clusters were established by previous pioneering work, and the Mn doped ZnSe clusters had been investigated, but the stable clusters in the ferromagnetic state have not been found yet. Objective: Our work is mainly based on Mn doped clusters (Mn2Zn10Se12) and C codoped clusters (Mn2Zn10Se11) structure, magnetic properties through theoretical calculations. Methods: First principle density functional theory calculation with Dmol3 is used to execute all calculations. Results: Mn atoms prefer to substitute the nearest neighbor Zn atom sites in the rhombi part, and C atom prefers to occupy Se atom sites with shortest Mn-C bond length in Zn12Se12 nanocluster doping. Mn doped clusters (Mn2Zn10Se12) are in antiferromagnetic states and the most stable C codoped clusters (Mn2Zn10Se11) are in ferromagnetic states. Magnetic behavior localized at the 3d orbitals of transitional metal Mn, 4p orbital of atom Se and 2p orbital of C atom. Mn2Zn10Se12 clusters are in antiferromagnetic states as the p-d hybridization introduced Mn-Mn superexchange mechanism. For the ferromagnetism of Mn2Zn10Se12 nanocluster, hole mediated double exchange mechanism introduced by C atom p-d hole state hybridization has been suggested. Conclusion: The codoping of C atom can stabilize the ferromagnetism of clusters through hole mediated double exchange mechanism, which may be meaningful for the exploring materials for cluster- assembled spin-electronic devices.

Nitride-incorporated W-Fe-S double cubane clusters: terminal ligand substitutions and redox behaviors.

Structural mimicking of the nitrogenase FeMo cofactor has long been a challenge in synthetic inorganic chemistry and bioinorganic chemistry. This already very tough task had become even harder after the discovery of an interstitial light atom, which was later evidenced to be carbide. From a synthetic point of view, to introduce such a 2p atom into the core of a Fe-S cluster would have to overcome the coordination competition from overwhelming sulfide ligands. Recently, we have reported a controlled synthetic strategy named redox metathesis based on template-assisted structure design, and have successfully synthesized a couple of nitride-incorporated edge-bridged double cubane (N-EBDC) W-Fe-S clusters. In this work, we have systematically studied the terminal ligand substitutions of heteroleptic N-EBDC clusters, utilizing ethanethiolate, thiophenolate, p-thiocresolate, azide, and methoxide to replace the terminally bound chloride ligands. Structural analysis of this family of N-EBDC clusters reveals that different terminal ligands affect the fine structures of the cluster cores at different levels. Further studies by cyclic voltammetry indicate that these N-EBDC clusters with distinct terminal ligands exhibit different redox behaviors, furnishing in-depth information on the electronic structure of these clusters potentially related to their reactivity. This study provided useful information for the investigation of nitrogenase related Fe-S clusters toward structural and functional mimicking of the nitrogenase FeMo cofactor.

Extraction of baryonia from the lightest antiprotonic atoms

Anti-protonic hydrogen and helium atoms are analyzed. Level shifts and width are expressed in terms of $\bar{p}$-nucleon sub-threshold scattering lengths and volumes. Experimental data are compared to results obtained from the 2009 version of the Paris $N\bar{N}$ interaction potential. Comparison with 1999 version is also made. Effects of $N\bar{N}$ quasi-bound states are discussed. Atomic 2P hyperfine structure is calculated for antiprotonic deuterium and the significance of new measurements is indicated.

Thermal reaction and luminescence of long-lived N 2D in N2 ice

Photochemistry of an N2 ice and thermal reaction of the irradiated sample were studied with vacuum-ultraviolet (VUV) light from a synchrotron. Concurrent detection of infrared absorption and visible emission spectra provide evidence for the generation of energetic products N (2D) and N (2P) atoms, N2 (A) molecule and linear-N3 (l-N3) radical after excitation of icy N2 at 121.6 nm. Irradiation at 190 nm is shown to be an effective way to eliminate the l-N3 radical. After the photolysis and photoelimination of the l-N3, we initiate synthesis of l-N3 via the thermal ramping of the sample in temperature range 3.5 to 20 K. In addition, the emission from the N (2D) atom was observed during the thermal ramping process. These behaviors indicate that a long-lived N (2Dlong) atom is generated in the VUV-photolyzed N2 ice. A comparison of the variations of the visible emission of N (2D) and the infrared absorption of l-N3 with time indicates that the long-lived N (2Dlong) dominated the thermal synthesis of l-N3 The results have enhanced suggestion and understanding of the conversion for nitrogen species in cold astrophysical environments with VUV irradiation.

Glow Discharge in a High-Velocity Air Flow: The Role of the Associative Ionization Reactions Involving Excited Atoms.

A kinetic scheme for non-equilibrium regimes of atmospheric pressure air discharges is developed. A distinctive feature of this model is that it includes associative ionization with the participation of N(2D, 2P) atoms. The thermal dissociation of vibrationally excited nitrogen molecules and the electronic excitation from all the vibrational levels of the nitrogen molecules are also accounted for. The model is used to simulate the parameters of a glow discharge ignited in a fast longitudinal flow of preheated (T0 = 1800–2900 K) air. The results adequately describe the dependence of the electric field in the glow discharge on the initial gas temperature. For T0 = 1800 K, a substantial acceleration in the ionization kinetics of the discharge is found at current densities larger than 3 A/cm2, mainly due to the N(2P) + O(3P) → NO+ + e process; being the N(2P) atoms produced via quenching of N2(A3∑u+) molecules by N(4S) atoms. Correspondingly, the reduced electric field noticeably falls because the electron energy (6.2 eV) required for the excitation of the N2(A3∑u+) state is considerably lower than the ionization energy (9.27 eV) of the NO molecules. For higher values of T0, the associative ionization N(2D) + O(3P) → NO+ + e process (with a low–activation barrier of 0.38 eV) becomes also important in the production of charged particles. The N(2D) atoms being mainly produced via quenching of N2(A3∑u+) molecules by O(3P) atoms.

Structural and electronic properties of (TiO2)10 clusters with impurities: A density functional theory investigation

We report the structural, energetics, and electronic properties of free-standing binary clusters (TiO2)10 with substitutional metallic and non-metallic impurities. The selected (TiO2)10 cluster has tetrahedral symmetry and is the putative low energy structure for this size. The substitutional impurity can be located at a vertex (4 sites) or at an edge (6 sites). The former has a binding energy only 0.03 eV/atom less than the latter, so they can be considered as almost degenerate. A total of 28 impurities are considered in the present report. We study the edge substitutional place since this environment is very similar to the corresponding one in the bulk, which makes these system a possible model for the bulk-like structures. Another advantage of the cluster considered here is that its energy gap is as large as the one presented in the bulk phases (anatase and rutile). This system allows us to mimic the bulk behavior without the use of intrasite Coulomb corrections (U) usually applied to the 3d orbital electrons of Ti atoms Ud and 2p orbital electrons of the O atoms Up; they are generally applied as parameters to fit the real energy gap observed in bulk (TiO2) systems. We show results for the formation energies, energy gaps and magnetism suggesting a way to control the band gap by means of the use of the appropriate impurity used in the substitution.