Nitrogen Molecules Research Articles

Mechanism of long-range hydrophobic force based on cavitation of metastable liquid film

Hydrophobic force, a key driving force in colloid physicochemical system and biological macromolecular system, exhibits a distinct multi-scale effect. The prevailing scholarly consensus attributes long-range hydrophobic force to bubble bridging, facilitated by unstable liquid film cavitation, while short-range force is thought to arise from the reorganization of water molecules at the solid-liquid interface. However, a comprehensive theoretical study remains elusive. To further elucidate the mechanism of the long-range hydrophobic force based on unstable liquid film cavitation, we carry out systematic research on the long-range hydrophobic force between perfluorooctyl trichlorosilane hydrophobic particles and the surface, by utilizing atomic force microscopy (AFM) and molecular dynamics simulations. According to AFM force tests, the long-range hydrophobic force escalates incrementally with subsequent close contacts before reaching a plateau. On the tenth contact, the penetration curve exhibits a sudden jump to an adhesion distance of 502.01 nm. A distinct step in the retraction curve suggests the rupture of the cavitation bubble capillary bridge. Importantly, the classical capillary force mathematical model provides an effective fit for the penetration curve. Our calculations estimate the volume of the capillary bridge at 0.30 μm³, offering direct theoretical evidence of the unstable liquid film cavitation bubble capillary bridge. Further insights are gained from large-scale tensile molecular dynamics simulations by using GROningen MAchine for Chemical Simulations (GROMACS). The inherent correlation mechanism of the formation, evolution, and mechanical behavior of the cavitation bubble capillary bridge in the separation process of hydrophobic particles are further explored from a molecular perspective. The results demonstrate that the local pressure drop occurring at the moment of “jump-out” separation of the hydrophobic particles attracts nitrogen molecules to diffuse into the liquid film, thereby forming a cavitation bubble capillary bridge. Simultaneously, a jumping behavior is observed in the calculated spring potential curve at the moment of capillary bridge rupture. Finally, the influence of solution gas content on long-range hydrophobic force is investigated. There is a positive correlation between gas molecule content and both the growth rate of cavitation bubble capillary bridge volume and the length of capillary bridge stretch-rupture, further demonstrating the gas concentration dependence of long-range hydrophobic forces. In a word, revealing the long-range hydrophobic force mechanism based on the cavitation of unstable liquid film can enhance our understanding of the interaction between colloid physical chemistry and biological macromolecules. Meanwhile, hydrophobic force is the fundamental driving force of particle-bubble adhesion in mineral flotation system, and the revelation of its action mechanism has important guiding significance for regulating the actual mineral flotation process.

Nonadiabatic quantum dynamics explores non-monotonic photodissociation branching of N2 into the N(4S) + N(2D) and N(4S) + N(2P) product channels.

Vacuum ultraviolet (VUV) photodissociation of N2 molecules is a source of reactive N atoms in the interstellar medium. In the energy range of VUV optical excitation of N2, the N-N triple bond cleavage leads to three types of atoms: ground-state N(4S) and excited-state N(2P) and N(2D). The latter is the highest reactive and it is believed to be the primary participant in reactions with hydrocarbons in Titan's atmosphere. Experimental studies have observed a non-monotonic energy dependence and non-statistical character of the photodissociation of N2. This implies different dissociation pathways and final atomic products for different wavelength regions in the sunlight spectrum. We here apply ab initio quantum chemical and nonadiabatic quantum dynamical techniques to follow the path of an electronic state from the excitation of a particular singlet 1Σ+u and 1Πu vibronic level of N2 to its dissociation into different atomic products. We simulate dynamics for two isotopomers of the nitrogen molecule, 14N2 and 14N15N for which experimental data on the branching are available. Our computations capture the non-monotonic energy dependence of the photodissociation branching ratios in the energy range 108 000-116 000 cm-1. Tracing the quantum dynamics in a bunch of electronic states enables us to identify the key components that determine the efficacy of singlet to triplet population transfer and therefore predissociation lifetimes and branching ratios for different energy regions.

Recent progress in the advanced strategies, rational design, and engineering of electrocatalysts for nitrate reduction toward ammonia.

Ammonia is a valuable feedstock for most chemicals, pharmaceuticals, and fertilizer products. It is a promising carbon-free energy source. Under severe experimental circumstances (high temperature and high pressure), ammonia is manufactured industrially using the standard Haber-Bosch process. This process uses a lot of energy and emits a huge amount of CO2 into the environment. One method that is seen to be promising and could eventually replace the Haber-Bosch process is the electrocatalytic production of ammonia. However, in ambient conditions, the cleavage of the nitrogen molecule is exceedingly difficult. As a result, the yield of ammonia remains modest and the study's scope is still restricted to the lab. When the catalytic performance is significantly increased, nitrate and nitrite contaminations in water systems can be effectively removed and simultaneously transformed into energy sources if nitrites or nitrates are employed as nitrogen sources instead of nitrogen gas. This may become a new substitute for the synthesis of ammonia, but nitrate and nitrite reduction are not getting enough attention. In this review, we discuss the performance of the electrocatalytic nitrate reduction reaction, which includes cycling stability, reactivity, selectivity, and faradaic efficiency. Following this summary, we look into the crucial elements, the rate-determining step, and the reaction mechanisms that govern the performance of the nitrate reduction reaction. In order to support the practical use of the electrocatalytic nitrate reduction reaction, we finally provided a summary of the challenges and future directions guiding the design of efficient catalyst and reaction systems.

In English

Comparative characterization of the particulate morphology and texture of various silicas (fumed silicas, silica gels, ordered mesoporous silicas) and carbons (chars and activated carbons, AC) is of interest from both theoretical and practical points of view since it allows one better understanding of advantages and disadvantages of various adsorbents upon their interactions with different adsorbates, co-adsorbates, and solutes in various dispersion media. Complete characterization needs application of a certain set of methods that is analyzed in the present paper. It is shown that the main difference in the textural characteristics of silica and carbon adsorbents is due to the absence (silicas) or presence (carbons) of nanopores in nanoparticles (NP). A great contribution of these pores in strongly activated carbons provides the specific surface area values greater by an order of magnitude than that of fumed silicas. Despite a high activation degree of AC, contribution of closed pores or pores inaccessible for nitrogen molecules remains relatively large in contrast to fumed silica A–300 composed of nonporous nanoparticles synthesized in the flame at higher temperature (~80% of melting temperature, Tm, for amorphous silica) than carbon activation temperature (~25%of Tm for carbons). Therefore, the pores inaccessible for nitrogen molecules in fumed silica could be attributed to narrow voids around contact area between neighboring NP in their aggregates, but for AC, there are both closed pores and open nanopores inaccessible for nitrogen molecules. For complete characterization of the morphology and texture of various adsorbents, such methods as transmission and scanning electron microscopies, probe (nitrogen, argon) adsorption, smallangle X-ray scattering (SAXS)and X-ray diffraction (XRD)could be used with appropriate software to analyze the data. The latter is especially important for the analyses of indirect data (e.g., adsorption, SAXS, XRD) characterizing the materials.

Formation Mechanisms of Electronically Excited Nitrogen Molecules from N + N2 and N + N + N Collisions Revealed by Full-Dimensional Potential Energy Surfaces.

This work reports six new full-dimensional adiabatic potential energy surfaces (PESs) of the N3 system (four 4A″ states and two 2A″ states) at the MRCI + Q/AVQZ level of theory that correlated to N2(X1Σg+) + N(4S), N2(X1Σg+) + N(2D), N2(A3Σu+) + N(4S), N2(B3Πg) + N(4S), N2(W3Δu) + N(4S), and N(4S) + N(4S) + N(4S) channels. The neural networks with a proper account of the nuclear permutation invariant symmetry of N3 were employed to fit the PESs based on about 4000 ab initio points. The accuracy of the PESs was validated by excellent agreement on the equilibrium bond length, vertical excitation energy, and dissociation energy with experimental values. Two possible mechanisms of the formation of N2(A) were found. One is that the collision occurs between N2(X) and N(4S) in the 14A″ state, followed by a nonadiabatic transition through the conical intersection with the 24A″ PES, resulting in the formation of the N2(A) + N(4S) product. The other takes place in the collision among three N(4S) atoms in the adiabatic 24A″ state, and then, N2(A) + N(4S) is formed. This is the first systematical research of the N3 system focusing on the formation of the excited states of N2 via both adiabatic and nonadiabatic pathways.

Artificial Photosynthesis of Ammonia by Semiconducting Plasmonic NIR Energy

Artificial photosynthesis of ammonia is one of the most promising paths toward carbon neutrality and sustainability. However, nitrogen photo-fixation to produce ammonia in ultrapure water is still challenging due to the thermodynamic and kinetic requirements of the nitrogen reduction reaction. An ideal photocatalyst is expected to have energetic electrons to drive the nitrogen reduction reaction, as well as enough affinity for chemisorption and activation of nitrogen molecules at the surface. Compared with plasmonic metal catalysts, plasmonic semiconducting nanomaterials are excellent candidates due to the tunable plasmon absorption over a wide range of spectra allowing efficient utilization of solar energy, abundant hot carriers that may overcome the interfacial energy barriers, and low-cost. The localized surface plasmonic resonance (LSPR) effects can also promote charge separation and interfacial transfer. Here, we report metal oxides with tunable oxygen concentration and copper chalcogenides with tunable copper deficiency for photocatalytic nitrogen reduction in ultrapure water. Efficient ammonia production has been achieved under near-infrared (NIR) light illumination. We have demonstrated that for plasmonic semiconducting photocatalysts, the performance is not only dictated by the defects, their negative effects in trapping carriers are also important. Figure 1

The use of low-temperature plasma for disinfection of open surfaces of industrial premises

The results of research on inactivation of microorganisms on open surfaces of poultry houses using low-temperature non-equilibrium plasma are presented. AC electrospark discharge at atmospheric pressure was used as its source. Discharge types are streamer, flare. The simultaneous effect of electromagnetic fields, charged particles and chemically active compounds formed by electrospark discharge on the efficiency of pathogenic microflora inactivation for various surfaces (acrylic primer, epoxy resin, yacht varnish, concrete-graphite mixture) is considered. The material to be treated (a biological model of the bedding surface of the floor in the poultry house with the applied protective layer) is installed after the electrospark discharge chamber blown with plasmaforming gas (atmospheric air). The main affecting factors are active chemical compounds: ozone; free radicals (OH, O, O2), ultraviolet radiation in the range of 750–1600 THz, electromagnetic radiation from 50 Hz to 980 MHz, charged particles and vibrationally excited nitrogen and oxygen molecules. Characterizations of electromagnetic radiation flux density at electrospark discharge are obtained. According to the research results, the maximum effect of treatment of exposed surfaces with low-temperature non-equilibrium plasma is achieved when epoxy resin is used as a surface protection material. The number of inactivated microorganisms at exposure of 10-20 s reaches 100%. When inactivating microorganisms on exposed surfaces, it is not economically feasible to take exposure time longer than 20 s. The studies found no significant difference when using streamer or flare discharges to treat outdoor facility surfaces.

A DFT study on nitrogen enhancing mechanism of SRF niobium cavity performance

High-temperature nitriding has been shown to improve the quality factor (Q) of the superconducting radio frequency (SRF) cavity recently, while its inherent promoting mechanism is still unclear. Therefore, based on first-principles calculations, the adsorption and dissociation processes of nitrogen molecules on the Nb(110) surface, and the adsorption, diffusion processes of nitrogen atoms on the Nb(110) surface, were studied in this paper to explain the principle of its performance improvement. To establish the reaction mechanism, adsorption preference sites were determined. All possible reaction paths were investigated for each step including the energy barrier based on the climbing image nudged elastic band (CI-NEB) method. We establish multiple reaction paths and the only optimal one was found. It is found that the Nb(110) surface can facilitate the dissociation of nitrogen molecules (with only a 1.14 eV energy barrier), and nitrogen atomic energy can readilyreach the subsurface (only a 1.73 eV energy barrier). Still, the high energy barrier (up to 6.64 eV) prevents it from diffusing inward. This revelation provides the nitriding mechanism of pure niobium and the rationale for enhancing niobium cavity performance after nitrogen mixing.

Sterilization Ability by Microwave UV-ozone Generator

The 253.7 nm UV light emitted from mercury lamps is known as germicidal radiation. Additionally, it emits UV light with a shorter wavelength of 184.9 nm. This UV wavelength can generate ozone (O3) from oxygen molecules (O2) in the air. Ozone has been shown to effectively inactivate various pathogenic microorganisms. However, they must decompose quickly because they are harmful to the human body. Methods for decomposing ozone include a thermal decomposition method, a chemical cleaning method, an activated carbon method, and the like. However, there is no practical or efficient treatment method. Ozone generation methods include the silent discharge method, electrolytic method, photochemical reaction method, high-frequency discharge method, and radiation method. The most efficient method is silent discharge, which is concerned with nitrogen oxide (NOX) generation caused by nitrogen molecules in the air, and deterioration of the electrodes during use is problematic. Furthermore, nitrogen oxides react with water in the gaseous phase to produce nitric acid. Nitric acid reacts with several metals to form nitrates. A sterilization device using highconcentration ozone has not been put to practical use because of the lack of an efficient method for decomposing ozone and the corrosion of metals. The UV-ozone generation method using microwave plasma used in this study can generate UV light by applying 2.45 GHz microwaves to a quartz electrodeless bulb filled with mercury. By changing the glass material and emitting UV light at different wavelengths, it is possible to develop a UV-ozone generator that can selectively generate and decompose ozone. Furthermore, since 184.9 nm UV specifically acts on oxygen molecules, NOX is not generated. Additionally, 253.7 nm UV, which is emitted at the same time as 184.9 nm UV, can easily decompose ozone into O2

A buffer-gas trap for the NEPOMUC positron beam: optimization studies with electrons

Buffer-gas traps (BGTs) use inelastic interactions with nitrogen molecules to capture positrons from a continuous beam. These devices are invaluable for high-resolution studies of matter–antimatter interactions, antihydrogen research and positronium laser spectroscopy. We present a new project with the goal of producing a non-neutral plasma containing ${\sim }10^8$ low-energy positrons by installing a BGT on the NEPOMUC (NEutron induced POsitron source MUniCh) high-intensity positron beam. Details of the BGT are outlined and results are presented from experiments in which an electron beam, with a similar intensity and energy spread to the remoderated NEPOMUC beam, was used to create pulses of non-neutral electron plasma. The device is a vital component of the APEX (A Positron Electron eXperiment) project, which aims to create a low-temperature electron–positron pair plasma.

Numerical study of nitrogen oxides chemistry during plasma assisted combustion in a sequential combustor

Plasma Assisted Combustion (PAC) is a promising technology to enhance the combustion of lean mixtures prone to instabilities and flame blow-off. Although many PAC experiments demonstrated combustion enhancement, several studies report an increase in NOx emissions. The aim of this study is to determine the kinetic pathways leading to NOx formation in the second stage of a sequential combustor assisted by Nanosecond Repetitively Pulsed Discharges (NRPDs). For this purpose, Large Eddy Simulation (LES) associated with an accurate description of the combustion/NOx chemistry and a phenomenological model of the plasma kinetics is used. Detailed kinetics 0-Dimensional reactors complement the study. First, the LES setup is validated by comparison with experiments. Then, the NOx chemistry is analyzed. For the conditions of operation studied, it is shown that the production of atomic nitrogen in the plasma by direct electron impact on nitrogen molecules increases the formation of NO. Then, the NO molecules are transported through the turbulent flame without being strongly affected. This study illustrates the need to limit the diatomic nitrogen dissociation process in order to mitigate harmful emissions. More generally, the very good agreement with experimental measurements demonstrates the capability of LES combined with accurate models to predict the NRPD effects on both turbulent combustion and NOx emissions.

Surface tension and evaporation behavior of liquid fuel droplets at transcritical conditions: Towards bridging the gap between molecular dynamics and continuum simulations

The phase transition from subcritical to supercritical conditions, referred to as transcritical behavior, significantly impacts the evaporation and fuel–air mixing in high-pressure liquid-fuel propulsion systems. Transcritical behavior is characterized as a transition from classical two-phase evaporation to a single-phase gas-like diffusion regime as surface tension and latent heat of vaporization reduce. However, the interfacial behavior represented by the surface tension coefficient and evaporation rate during this transition which are crucial inputs for Computational Fluid Dynamics (CFD) simulations of practical transcritical fuel spray is still missing. This study aims at developing new evaporation rate and surface tension models for transcritical n-dodecane droplets using molecular dynamics (MD) simulations irrespective of the droplet size. As MD simulations are primarily limited to the nanoscale, the new models can bridge the gap between MD and continuum simulations and enable the direct application of these findings to microscopic droplets. A new characteristic timescale, i.e., “undroplet time,” is defined which marks the transition from classical two-phase evaporation to single-phase gas-like diffusion behavior. The undroplet time indicates the onset of droplet core disintegration and penetration of nitrogen molecules into the droplet, which occurs after the vanishment of the surface tension. By normalizing the time with respect to the undroplet time, the rate of surface tension decay, evaporation rate, and the rate of droplet mass depletion become independent of the droplet size. Calculation of pairwise correlation coefficients for the entire MD results shows that both surface tension coefficient and evaporation rate are strongly correlated with the background temperature, while pressure and droplet size play a less significant role past the critical point. Therefore, new models for surface tension coefficient and evaporation rate spanning from sub- to supercritical conditions are developed as a function of background pressure and temperature, which can be used in continuum simulations. The identified phase change behavior based on the undroplet time shows a good agreement with the phase change regime maps obtained using microscale experiments and nanoscale MD predictions.

The Sticking of N2 on W(100) Surface: An Improvement in the Description of the Adsorption Dynamics Further Reconciling Theory and Experiment.

The adsorption of nitrogen molecules on a (100) tungsten surface has been studied using a new potential energy surface in which long-range interactions are suitably characterized and represented by the Improved Lennard-Jones function. The new potential energy surface is used to carry out molecular dynamics simulations by adopting a semiclassical collisional method that explicitly includes the interaction with the surface phonons. The results of the sticking probability, evaluated as a function of the collision energy, are in good agreement with those obtained in the experiments and improve the already good comparison recently obtained with calculations performed using interactions from the Density Functional Theory method and corrected for long-range van der Waals contributions. The dependence of trapping probability on the surface temperature for a well-defined collision energy has also been investigated.

Measurement and reduction of Ar metastable densities by nitrogen admixing in electron beam-generated plasmas

Electron beam (e-beam) generated plasmas are useful for material processing applications such as deposition and etching because the plasmas deliver a large fluence of very low energy of ions to surfaces. Metastable species produced in the beam-region can also transport significant energy to the plasma periphery and surfaces. In this work, we have investigated the spatially resolved density of metastable Ar 1s5 species produced in an Ar and Ar/N2 e-beam generated plasma at pressures of 60–67 mTorr using laser-induced fluorescence (LIF). The experiments provide the first direct measure of absolute density and reduction of Ar 1s5 in an e-beam generated plasma when argon is diluted with nitrogen. These results are consistent with previous predictions of numerical modeling and measurements using optical emission spectroscopy. The present spatially resolved LIF measurements directly quantify the reduction of Ar 1s5 in the e-beam generated plasma by nitrogen admixing. This reduction was observed in the region of the electron beam and in the plasma periphery, where substrates are usually placed. For example, up to a threefold reduction of the density of Ar 1s5 was measured when the argon background was diluted with 15.5% nitrogen at pressure of 60 mTorr. Ar 1s5 reduction is attributed to excitation exchange with nitrogen molecules as well as the cooling of plasma electrons via inelastic collisions with nitrogen molecules.

Generation of radiation on forbidden transitions in the region of 654-658 nm in an acoustoplasmic medium

In the region of the first positive system (FPS) band of spectrum of nitrogen in acoustoplasma, under laboratory conditions, the generation of intense lines was experimentally obtained at forbidden transitions of a singly ionized nitrogen molecule at 654.81 and 658.36 nm. The intense lines obtained correspond to the stimulated emission mechanism. The intensity of the forbidden lines significantly (up to 17 times) exceeded the intensity of neighboring lines in the spectrum of the first positive system band of nitrogen. Spectroscopic studies did not allow resolution of the rotational spectrum. However, the spectral width for both lines at forbidden transitions is much smaller than the FPS bandwidth of nitrogen. The result obtained is explained by an analogue of Raman scattering and an acoustoplasmic medium, which remove the prohibitions characteristic of dipole radiation.

Characterization of thermal decomposition mechanism and combustion performance of 4,4’‐azobis(1,2,4‐triazole)**

Abstract4,4’‐azobis(1,2,4‐triazole) (ATRZ), as a representative of high‐nitrogen compound, has attracted extensive interests. This work explores the thermal decomposition mechanism and combustion performance of ATRZ. The thermogravimetry‐differential scanning calorimetry‐fourier transform infrared spectroscopy (TG‐DSC‐FTIR) of ATRZ was carried out at heating rate of 10 °C/min in an argon atmosphere. ATRZ has two peak exothermic temperatures, 110.24 °C and 306.85 °C respectively. The exothermic peak at 110.24 °C is the decomposition of ATRZ tiny debris, and the exothermic peak at 306.85 °C is the decomposition of the main part of ATRZ. The pyrolysis‐gas chromatography mass spectrometry (PY‐GC/MS) of ATRZ was carried out at 350 °C in an argon atmosphere. By combining TG‐DSC‐FTIR and PY‐GC/MS, the thermal decomposition mechanism of ATRZ was speculated. The main reaction in the ATRZ pyrolysis process is the cleavage of two N−N single bonds in the nitrogen bridge, forming a nitrogen molecule and two triazole rings, which is the majority of the first step decomposition reaction. At the same time, a small number of triazole rings break off to form other intermediates. A small amount of nitrogen gas is generated and a large number of CN clusters are formed. Under the same testing conditions, ATRZ has a higher combustion heat (19318 J/g) than other traditional CHNO energetic materials. By comparing the laser ignition combustion of ATRZ and ATRZ+RDX, the combustion temperature of ATRZ+RDX is higher and the combustion duration is longer. The introduction of CHNO type ammonium nitrate explosives promotes the energy release of ATRZ.

Sequential N2 Adsorption by the Nanopore Entrance Filling Scheme in Nanopores of Carbon Nanotubes.

The adsorption dynamics and mechanism of nitrogen molecules in 1-7 nm carbon nanotubes (CNTs) at 77 K were investigated by experiments and molecular dynamics simulations. The adsorbed nitrogen amount rapidly increased in 7 nm CNTs, while it gradually increased in 1 and 3 nm CNTs. The gradual increase in 3 nm CNTs was unexpected because of the presence of sufficient adsorption sites and the weak adsorption potential of nitrogen. The molecular dynamics simulations indicated that molecules were condensed in the entrance of nanopores after monolayer adsorption in 3 nm CNTs and monolayer and bilayer adsorption in 5 nm CNTs, called nanopore entrance filling. The proposed adsorption mechanism of nitrogen molecules in CNT nanopores is as follows: first, layer-by-layer adsorption occurs on monolayer sites, followed by preferential adsorption at the nanopore entrance. Consequently, preadsorbed molecules form a fluidic pore neck similar to an ink-bottle pore. Then, newly adsorbed molecules are condensed on the fluidic pore neck, and condensed molecules in the nanopore entrance finally move into the inner part of the nanopore. The proposed sequential adsorption mechanism via nanopore entrance filling without pore blocking starkly differs from micropore filling in micropores and layer-by-layer adsorption associated with capillary condensation in mesopores.

Orientational order parameter and mean square displacement of solid heavy nitrogen in the low-temperature phase. Experimental data

This work presents the results of the analysis of the temperature dependence of the x-ray reflection intensity from solid heavy nitrogen in the ordered phase. The temperature dependence of the behavior of the orientational order parameter and mean square displacement of 15N2 molecules obtained from x-ray data is plotted. Based on the dependencies obtained, the orientational order parameter was determined at 0 K, which is 12% higher than the orientational order parameter obtained in theoretical works. It was found that the heavy nitrogen molecule “freely” rotates in the crystal at temperatures above 45 K.

Synergistic multi-adsorption of N2 on MoS2 supported single metal atoms: Enhancing electroreduction of nitrogen to ammonia

MoS2-supported transition metal single atom (TM/MoS2) is expected to exhibit good performance in N2 reduction reaction (NRR). Based on systematically investigations of the stability and potential electrocatalytic nitrogen reduction reaction (NRR) performance of 27 types of TM/MoS2, V(Nb, Ta)/MoS2 exhibit good structure stability, excellent N2 activity and high ammonia (NH3) selectivity. Three nitrogen molecules are effectively captured on V(Nb, Ta)/MoS2 and the multi-adsorption of nitrogen make Mo-top site energy favorable for all the *3N2–V(Nb, Ta)/MoS2 especially for *3N2–Nb/MoS2 the energy favorable sites shift from hollow site to Mo-top site. The NRR proceeds via distal pathway, along which the limiting potentials are calculated to be −0.55, −0.42, −0.34 V for V/MoS2, Nb/MoS2 and Ta/MoS2, respectively. The transformation of Nb/MoS2 and the multi-adsorption of *N2 make the *N2 more negatively charged and more effectively activated than single adsorbed *N2, meanwhile suppressing the production of hydrogen. This work also shows the coordination difference with and without reactants adsorption and the impact on catalytic performance, which raises the importance of considering the stability of intermediates along reaction paths during theoretical design of new catalysts.

Molecular-frame photoelectron angular distributions during double core-hole generation in and molecules

Angular distributions of photoelectrons emitted upon double core-hole (DCH) generation in nitrogen and oxygen molecules are studied theoretically in the frame of a molecular reference. The respective electronic structure calculations are performed by the single center method for photoelectron kinetic energies up to 40 eV in the relaxed-core Hartree–Fock approximation. The molecular frame photoelectron angular distributions are computed for single-site and two-site DCH creation processes and further analyzed for different orientations of the molecular axis with respect to the electric field vector of linearly polarized incident light and for localized or delocalized emitting atomic site scenarios. The present theoretical results provide reliable predictions for future experiments with high-repetition free-electron lasers.