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Understanding the properties of molecular nitrogen N2 at extreme conditions is the fundamental problem for atomistic theory and the important benchmark for the capabilities of first-principles molecular dynamics (FPMD) methods. In this work, we focus on the connection between the dynamics of ions and electronic excitations in warm dense N2. The restricted open-shell Kohn–Sham method gives us the possibility to reach relevant time and length scales for FPMD modeling of an isolated exciton dynamics in warm dense N2. Wannier localization sheds light on the corresponding mechanisms of covalent bond network rearrangements that stand behind polymerization kinetics. FPMD results suggest a concept of energy transfer from the thermal energy of ions into the internal energy of polymeric structures that form in warm dense N2 at extreme conditions. Our findings agree with the thermobaric conditions for the onset of absorption in the optical spectroscopy study of Jiang et al. [Nat. Commun. 9, 2624 (2018)]. [ABSTRACT FROM AUTHOR]

Up to 17 GPa, the crystalline phases of N2 are characterized by pronounced orientational disorder, whereas the higher-pressure phases of molecular N2 are ordered. This raises the question about long-term relaxation of orientational disorder within the low- to intermediate-pressure regime. Here, this question is addressed by comparing synthetic with natural, chemically pure, solid N2 that resides as inclusions in diamonds at 300 K for about 108 years at pressures up to 11 GPa. It is shown that disorder prevails at 8.7 GPa, 300 K, where both synthetic and natural N2 assume the same structure. However, at 10.8 GPa, natural solid N2 exhibits monoclinic distortion and partial orientational ordering of the molecules, both of which are not observed in synthetic material. This difference is interpreted as the result of long-term structural relaxation. The ordering mechanism is examined and placed into the context of the δ- to ε-N2 transition. We present explanations for the absence of complete ordering of δ-N2. [ABSTRACT FROM AUTHOR]

The contribution of atomic nitrogen is fairly possible in plasma-assisted catalytic synthesis of ammonia since it has high adsorption probabilities on solid surfaces. On the other hand, recently, the contribution of vibrational excited molecular nitrogen to ammonia synthesis has been discussed. In this work, we compared the fluxes of atomic nitrogen and vibrational excited molecular nitrogen with the rate of plasma-assisted ammonia synthesis. We employed an atmospheric-pressure nitrogen plasma jet, and the spatial afterglow of the plasma jet and a hydrogen flow irradiated the surface of a ruthenium catalyst. The fluxes of atomic nitrogen and vibrational excited molecular nitrogen were measured by two-photon absorption laser-induced fluorescence spectroscopy and laser Raman scattering, respectively. The synthesis rate of ammonia had a positive correlation with the flux of vibrational excited molecular nitrogen, while the variation of the synthesis rate with the gas flow rate was opposite to the flux of atomic nitrogen. The experimental results indicate the contribution of vibrational excited molecular nitrogen to the synthesis of ammonia using the atmospheric-pressure plasma, where the flux of vibrational excited molecular nitrogen is more than four orders of magnitude higher than that of atomic nitrogen. [ABSTRACT FROM AUTHOR]

Wave packet interferometry with vacuum ultraviolet light has been used to probe a complex region of the electronic spectrum of molecular nitrogen, N2. Wave packets of Rydberg and valence states were excited by using double pulses of vacuum ultraviolet (VUV), free-electron-laser (FEL) light. These wave packets were composed of contributions from multiple electronic states with a moderate principal quantum number (n ∼ 4–9) and a range of vibrational and rotational quantum numbers. The phase relationship of the two FEL pulses varied in time, but as demonstrated previously, a shot-by-shot analysis allows the spectra to be sorted according to the phase between the two pulses. The wave packets were probed by angle-resolved photoionization using an infrared pulse with a variable delay after the pair of excitation pulses. The photoelectron branching fractions and angular distributions display oscillations that depend on both the time delays and the relative phases of the VUV pulses. The combination of frequency, time delay, and phase selection provides significant control over the ionization process and ultimately improves the ability to analyze and assign complex molecular spectra. [ABSTRACT FROM AUTHOR]

Unlike naturally occurring oxide crystals such as ruby and gemstones, there are no naturally occurring nitride crystals because the triple bond of the nitrogen molecule is one of the strongest bonds in nature. Here, we report that when the transition metal scandium is subjected to molecular nitrogen, it self-catalyzes to break the nitrogen triple bond to form highly crystalline layers of ScN, a semiconductor. This reaction proceeds even at room temperature. Self-activated ScN films have a twin cubic crystal structure, atomic layering, and electronic and optical properties comparable to plasma-based methods. We extend our research to showcase Sc's scavenging effect and demonstrate self-activated ScN growth under various growth conditions and on technologically significant substrates, such as 6H–SiC, AlN, and GaN. Ab initio calculations elucidate an energetically efficient pathway for the self-activated growth of crystalline ScN films from molecular N2. The findings open a new pathway to ultralow-energy synthesis of crystalline nitride semiconductor layers and beyond. [ABSTRACT FROM AUTHOR]

In recent years numerous satellite data on the yellow glow of the sodium layer (located at an altitude of 85–95 km from the Earth's surface) have become available. Studies of optical activity at sodium D‑line frequencies are necessary for a better understanding of the plasma-chemical processes occurring in the mesosphere. It should be taken into account that these processes occur in a neutral environment, where molecular nitrogen is the main component. In this study the analytical numerical expressions for the elements of a 3 × 3 matrix of the interaction between Na(2Pj) and N2() and the interaction potential between Na(2S1/2) and N2() are obtained at medium and large interparticle distances that determine the collisional broadening of the radiation lines. The exchange, quadrupole–quadrupole, dispersion, and spin–orbit interactions are taken into account. The exchange interaction between the valence Na electron and N2() molecule is described by the local Hellman pseudopotential. The effect of the overlap between Na(2S1/2,2Pj) and N2() electron densities is taken into account in the evaluation of long-range quadrupole–quadrupole and dispersion interactions. [ABSTRACT FROM AUTHOR]

In the present study, a Cu2O@PCz electrode for the nitrogen reduction reaction is proposed; this electrode takes advantage of the catalytic properties of Cu2O in conjunction with conducting polymers such as polycarbazole (PCz). This combination demonstrates an improvement in the catalytic activity and higher stability of this metal oxide in nitrogen electro-reduction reaction (NRR) and nitrogen oxoanion electro-reduction reaction (NORR) processes under aqueous conditions. On this basis, the material synthesized on FTO (SnO2 : F), Cu2O@PCz, exhibits a faradaic efficiency of around 38.83%, together with an NH3 productivity of 1.83 μg h−1 cm−2 in NRR type processes, on applying a potential of −0.8 V (V vs. Ag/AgCl). Similarly, in NORR type processes, the material exhibits NH3 and N2H4 productivity. The latter is the most relevant in terms of the yields obtained. Specifically, using nitrite (NO2−), an efficiency of around 77.72% was obtained, together with a formation rate of 37.02 μg h−1 cm−2 at a potential of −0.8 V (V vs. Ag/AgCl). Although N2H4 is a by-product of ammonia formation, this molecule can be considered an intermediate, which broadens the scope of this study for future research into the production of green chemicals. Finally, this research presents promising new routes for the production of NH3 at room temperature, highlighting the potential of low-cost materials, easy synthesis, and enhanced stability. [ABSTRACT FROM AUTHOR]

The authors study characteristics of lasing on molecular nitrogen ions in laser plasma created by a femtosecond radiation pulse. The maximum intensities at wavelengths of 391.4 and 427.8 nm are observed at nitrogen pressures of 30 and 500 mbar, respectively. The divergence of radiation is tens mrad and close to geometric. The pulse length at a wavelength of 391.4 nm varies from 1.83 to 3.5 ps upon changing the focal length of the lens from 15 to 40 cm. [ABSTRACT FROM AUTHOR]

We studied luminescence accompanied an injection of the nitrogen-helium gas mixture after passing discharge into dense cold helium gas. Initially, when the experimental beaker was filled with superfluid helium and the nitrogen-helium gas was injected into bulk superfluid helium at T ≈ 1.5 K, the dominant band in the emission spectra was the α-group of nitrogen atoms. At these conditions, the nanoclusters of molecular nitrogen with high concentrations of stabilized nitrogen atoms were formed. When superfluid helium was evaporated from the beaker and the temperature at the bottom of the beaker was increased to T ≈ 20 K, we observed a drastic change in the luminescence spectra. The β-group of oxygen atoms was dominated in the luminescence spectra, and the emission of the α-group became small. At high temperatures (T ≈ 20 K), most of the nitrogen atoms recombine on the surface of N2 nanoclusters with the formation of excited nitrogen molecules. We explained the effect of the enhancement of β-group emission by effective energy transfer from excited nitrogen molecules to the stabilized impurity oxygen atom inside N2 nanoclusters. [ABSTRACT FROM AUTHOR]

The results of simulation of radiation-chemical transformations in the primary coolant of a water-cooled water-moderated energy reactor (VVER) are presented. It has been shown that under conditions of intense irradiation, molecular nitrogen dissolved in the coolant exhibits chemical activity. The reaction of N2 with the excited hydroxyl radical initiates the formation of ammonia and nitrous acid. Further decomposition of ammonia produces only oxidized forms of nitrogen, with N2 acting as an intermediate product. Maintaining hydrogen and oxygen concentrations within normal limits in the ammonia water chemistry is possible only with constant dosing of NH3 and degassing of the coolant. In the case of water chemistry with H2 dosing (at the initial moment), on the contrary, a stationary regime is quickly established in the absence of disturbances, satisfying the requirements of VVER water chemistry standards. The difference between the two water chemistry systems is due to the presence of nitrogen in the NH3 molecule and its transformations as an element, regardless of the initial chemical form. [ABSTRACT FROM AUTHOR]

We report results of experimental studies on spectral, temporal, energy and spatial characteristics of coherent radiation at a wavelength of 391.4 nm [ transition of molecular nitrogen ion]. Lasing occurs in pure nitrogen under pumping by a radiation pulse with a duration of 70 fs at a wavelength of 950 nm. The lasing parameters are studied as functions of nitrogen pressure, pump beam energy, and its focusing conditions. Optimal values of pump energy (6 mJ) and nitrogen pressure (30 mbar) are determined. It is found that the divergence of radiation decreases with increasing focal length of the lens and correlates with the geometric dimensions of the laser plasma. It is also shown that with increasing specific pump power, the pulse duration decreases and can be close to the transform-limited one (1.83 ps). [ABSTRACT FROM AUTHOR]

A study is performed of the kinetics of triplet states B3Πg, W3Δu, C3Πu of molecular nitrogen at the altitudes of Titan's middle atmosphere during the precipitation of cosmic rays. The intramolecular and intermolecular transfer of electron energy during inelastic collisions between electronically excited molecular nitrogen and molecules of N2, CH4, and CO is considered, as is the interaction between electronically excited N2 molecules and molecules of acetylene C2H2 and ethylene C2H4 in the middle atmosphere of Titan at altitudes of 50–250 km. The dominance of reactions with metastable molecular nitrogen N2() in the formation of C2H and C2H3 radicals at these heights is shown for the first time. [ABSTRACT FROM AUTHOR]

Interactions of N2 at oxide surfaces are important for understanding electrocatalytic nitrogen reduction reaction (NRR) mechanisms. Interactions of N2 at the polycrystalline vanadium oxide/vapor interface were monitored at room temperature and total pressures up to 10−1 Torr using Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). The oxide film was predominantly V(IV), with V(III) and V(V) components. XPS spectra were acquired in environments of both pure N2 and equal pressures of N2 and H2O vapor. In pure N2, broad, partially resolved N1s features were observed at binding energies of 401.0 and 398.7 eV, with a relative intensity of ∼3:1, respectively. These features remained upon subsequent pumpdown to 10−9 Torr. The observed maximum N surface coverage was ∼1.5 × 1013 cm−2—a fraction of a monolayer. In the presence of equal pressures of H2O, the adsorbed N intensity at 10−1 Torr is ∼25% of that observed in the absence of H2O. The formation of molecularly adsorbed H2O was also observed. Density functional theory-based calculations suggest favorable absorption energies for N2 bonding to both V(IV) and V(III) cation sites but less so for V(V) sites. Hartree–Fock-based cluster calculations for N2–V end-on adsorption show that experimental XPS doublet features are consistent with the calculated shake-up and normal, final ionic configurations for N2 end-on bonding to V(III) sites but not V(IV) sites. The XPS spectra of vanadium oxide transferred in situ between electrochemical and UHV environments indicate that the oxide surfaces studied here are stable upon exposure to the electrolyte under NRR-relevant conditions. [ABSTRACT FROM AUTHOR]

We have used the FERMI free-electron laser to perform time-resolved photoelectron imaging experiments on a complex group of resonances near 15.38 eV in the absorption spectrum of molecular nitrogen, N2, under jet-cooled conditions. The new data complement and extend the earlier work of Fushitani et al. [Opt. Express 27, 19702–19711 (2019)], who recorded time-resolved photoelectron spectra for this same group of resonances. Time-dependent oscillations are observed in both the photoelectron yields and the photoelectron angular distributions, providing insight into the interactions among the resonant intermediate states. In addition, for most states, we observe an exponential decay of the photoelectron yield that depends on the ionic final state. This observation can be rationalized by the different lifetimes for the intermediate states contributing to a particular ionization channel. Although there are nine resonances within the group, we show that by detecting individual photoelectron final states and their angular dependence, we can identify and differentiate quantum pathways within this complex system. [ABSTRACT FROM AUTHOR]

We report experimental data on rotating plasma disturbances in a quasi-steady direct-current magnetron discharge operating with molecular nitrogen at pressures of 27, 40, 67, and 133 Pa. Experiments with a segmented anode measuring the local current flow reveal up to 12 coherent structures ("spokes") propagating in the + E × B and − E × B azimuthal directions. The current–voltage characteristics are studied and found to follow a negative resistance profile at the lower discharge currents. The existence of coherent structures and the number of spokes observed depend on the discharge current and operating pressure. Lower pressures are more favorable to the retrograde − E × B spoke rotation, which is observed in the 27, 40, and 67 Pa discharges. The results are interpreted with a gradient-driven drift wave model, and using the dispersion relation, we show that the propagation direction depends on the orientation of the local electric field within the plasma. Using an electron fluid model, we show how experimental conditions can lead to field reversals that generate − E × B spoke rotation in the lower pressure discharges. [ABSTRACT FROM AUTHOR]

Based on models of the electronic kinetics of triplet and singlet states of molecular nitrogen and singlet states of molecular oxygen for the Earth's middle atmosphere, we calculated the intensity profiles of the bands of the first and second positive N2 systems, the Lyman–Birge–Hopfield N2 bands, and the infrared O2 bands in the case of precipitation of high-energy protons during the GLE65, GLE67, GLE69, and GLE70 events of solar cycle 23. Calculations have shown that almost over the entire interval of altitudes of 20–80 km, there is a significant contribution from the processes of quenching some electronically excited states of N2 and O2 during molecular collisions. The kinetics of O2 singlet states at the altitudes of the middle atmosphere during proton precipitation is considered taking into account both direct excitation by high-energy particles and intermolecular processes of electron excitation transfer. [ABSTRACT FROM AUTHOR]

We investigated the vibrational temperature of molecular nitrogen in the downstream of helicon-wave excited helium and argon-based plasmas. It was confirmed by optical emission spectroscopy that the major part of the helium plasma was at a recombining state and it had an ultralow electron temperature of approximately 0.1Â eV. In spite of the ultralow electron temperature, the vibrational temperature of molecular nitrogen, which was added into the helium plasma, was higher than that in the argon-based plasma at an ionizing state with an electron temperature of 1.7Â eV. According to the relationship between the rate coefficient of electron impact vibrational excitation and the electron temperature, the higher vibrational temperature in the helium plasma is not attributable to the more efficient vibrational excitation. Therefore, the higher vibrational temperature is owing to the less efficient destruction of vibrational excited states in the helium plasma with the ultralow electron temperature. [ABSTRACT FROM AUTHOR]

The potential energy curves for molecular ions up to N 2 4 + are calculated in an ab initio manner using the multi configurational self-consistent field method. Specifically, we implement in an automatic way a previously used double loop optimisation scheme within the multi configurational self-consisted field method. We obtain the potential energy curves up to N 2 4 + ions with any combination of core, inner valence, and outer valence holes. Finally, we provide the code used to generate these potential energy curves. [ABSTRACT FROM AUTHOR]

The structural evolution of local coordination environments of single-atom catalysts (SACs) under reaction conditions plays an important role in the catalytic performance of SACs. Using density functional theory calculations, the possible structural evolution of transition metal single atoms supported by B/N codoped-graphene (TM–B2N2/G) under nitrogen reduction reaction (NRR) conditions is explored and the catalytic performance based on reconstructed SACs is theoretically evaluated. A novel nitrogen adsorption mode on TM–B2N2/G is discovered and the protonation of one of the N atoms results in the TM atoms binding with three N atoms, among which one associates with two B atoms (TM–N3B2/G). It is suggested that the N3B2/G supported tungsten single atom (W–N3B2/G) exhibits excellent N2 activity with a limiting potential of −0.27 V and high ammonia selectivity. Electronic structure analysis indicates that the coordination of N3B2/G redistributes the charge density of central W, shifts its d band center upward and strengthens the interaction of W and the adsorbed nitrogen molecule, thereby endowing it with better NRR performance, compared with that supported by pyridine-3N-doped graphene and pyrrolic-3N-doped graphene. [ABSTRACT FROM AUTHOR]

A study is performed of the kinetics of triplet states of molecular nitrogen at the altitudes of Titan's upper and middle atmosphere during the precipitation of high-energy electrons and cosmic rays. Collisional molecular processes with atmospheric components are considered for the first time in order to calculate concentrations of metastable molecular nitrogen . Numerical calculations show that inelastic molecular collisions result in the predominant accumulation of electronic excitation energy of metastable nitrogen at lower vibrational level ν = 0 and the altitudes of the middle atmosphere. [ABSTRACT FROM AUTHOR]

This minireview presents the results that show the potential of molecular nitrogen fixation by carbonyl cluster compounds of platinum metals at room temperature and atmospheric pressure to produce ammonia or its derivatives. Although the main attention is given to processes with the participation of derivatives of platinum and palladium, it was demonstrated that molecular nitrogen fixation is characteristic of all the platinum metals, except osmium. [ABSTRACT FROM AUTHOR]

We discuss peculiar features of electron scattering on the N2 molecule and the N2+ ion, that are important for modeling plasmas, Earth's and other planets' atmospheres. These features are, among others: the resonant enhancement of the vibrational excitation in the region of the shape resonance around 2.4 eV, the resonant character of some of electronic excitation channels (and high values of these cross sections, both for triplet and singlet states), high cross section for the dissociation into neutrals, high cross sections for elastic scattering (and electronic transitions) on metastable states. For the N2+ ion we discuss both dissociation and the dissociative ionization, leading to the formation of atoms in excited states, and dissociative recombination which depends strongly on the initial vibrational state of the ion. We conclude that the theory became an indispensable completion of experiments, predicting many of partial cross sections and their physical features. We hope that the data presented will serve to improve models of nitrogen plasmas and atmospheres. [ABSTRACT FROM AUTHOR]

The intensity profiles of the bands of the first and second positive N2 systems and the infrared atmospheric and atmospheric O2 systems were calculated based on models of the electronic kinetics of triplet states of molecular nitrogen and singlet states of molecular oxygen for the middle Earth's atmosphere in the case of the precipitation of high-energy protons into the Earth's atmosphere during the ground-level enhancement (GLE) (no. 69) on January 20, 2005. Calculations have shown that there is a significant contribution from the quenching of the B3Πg state during molecular collisions over nearly all of the considered altitude range of 20–80 km. The kinetics of O2 singlet states at altitudes of the middle atmosphere during proton precipitation is considered. Both direct excitation by high-energy particles and intermolecular processes of electron-excitation transfer are taken into account. It is shown that the quenching of the state during inelastic molecular collisions leads to a significant decrease in the intensities of the bands of the atmospheric system at the heights of the middle atmosphere. [ABSTRACT FROM AUTHOR]

In the interaction of high-energy electrons with gases of planetary atmospheres where the primary component is molecular nitrogen, a significant fraction of particle energy is spent on the excitation of electronically excited triplet states of N2. The processes of energy transfer from metastable molecular nitrogen to other components in the atmosphere of the Earth (a mixture of N2–O2–O gases), as well as in the atmospheres of Titan, Triton, and Pluto (a mixture of N2–CH4–CO gases), are considered. The paper discusses the processes in which metastable molecular nitrogen affects the kinetics of electronically excited atomic and molecular oxygen in the auroral ionosphere of the Earth. In addition, it is shown numerically for the first time that the contribution of to the formation of electronically excited carbon monoxide CO(a3Π) increases significantly with increasing density in the atmospheres of Titan, Triton, and Pluto, and becomes predominant for the lower vibrational levels of CO(a3Π). [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of a study of the temporal and spectral characteristics of lasing at transition of molecular nitrogen ions in laser plasma created by a radiation pulse with central wavelength of 950 nm, duration of 60 fs and energy of 10 mJ. The parameters of the active medium are analyzed and a possible mechanism for the formation of picosecond duration of the radiation pulse is discussed. [ABSTRACT FROM AUTHOR]

The results of the model estimate of the height of the lower limit of integration of the ratio of the concentrations of atomic oxygen and molecular nitrogen (n(O)/n(N2)) in the thermosphere according to observations using the Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics Global UltraViolet Imager (TIMED GUVI) method are presented. According to this observation technique, the lower limit of integration (h1) corresponds to the height at which the integral n(N2) takes on the value 1017 cm–2 within the range from the height of the satellite to h1. Estimates of the global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) showed that, for the conditions under consideration (January 2013 and March 2015), h1 varies in the range 148–164 km; h1 has diurnal, seasonal, latitudinal, and longitudinal variations; weakly depends on solar radiation; and significantly depends on geomagnetic activity within the above limits. To demonstrate the reproduction of the n(O)/n(N2) variations in the upper atmosphere of the Earth by the GSM TIP model, the measurements are compared with the results of the model calculations, which show their satisfactory agreement. [ABSTRACT FROM AUTHOR]

The efficient synthesis of ammonia using carbon-footprint-free hydrogen under mild conditions is a grand challenge in chemistry today. To achieve this objective, novel concepts are needed for the activation process and catalyst. This article briefly reviews catalytic activation of N2 for ammonia synthesis under mild conditions. The features of the various activation methods reported so far are summarized, looking chronologically back at progress in heterogeneous catalysts since the use of iron oxide for the Haber–Bosch process, and finally the technical challenges to be overcome are described. Establishing low work functions for the support materials of the metal catalysts is one key to reducing the activation barrier to dissociate N2. Surfaces of electride materials that preserve the character of the bulk are shown to be useful for this purpose. The requirements of desired catalysts are high efficiency at low temperatures, Ru-free compositions, and chemical robustness in the ambient atmosphere. [ABSTRACT FROM AUTHOR]

Resonance-enhanced multiphoton ionization (REMPI) is shown to offer an attractive strategy for population inversion of molecular nitrogen in an Ar: N2 gas mixture. We present a detailed analysis of the key processes leading to a population inversion of molecular nitrogen in a REMPI-pumped Ar: N2 gas mixture, including a (3 + 1) REMPI of argon atoms, conversion of the REMPI-generated atomic argon ions into molecular ions, and generation of long-lived metastable excited-state argon atoms through dissociative recombination, populating the C3πu states of molecular nitrogen. Population inversion achieved for the second-positive-band laser transitions of molecular nitrogen enables stimulated emission of ultraviolet radiation at 337 nm. A high selectivity of the REMPI process helps to radically reduce the depletion of the working medium through the ionization of N2, providing a pump mechanism that is ideally suited for the creation of a new type of a highly efficient nitrogen laser. [ABSTRACT FROM AUTHOR]

The luminescence-intensity profiles of the bands of the first and second positive systems of molecular nitrogen were calculated for the case of the precipitation of high-energy electrons with energies from 10 keV to 10 MeV into the atmosphere. The calculations showed that the contribution of the quenching of state B3Πg N2 increases during molecular collisions with an increase in the energy of electrons intruding into the atmosphere. This leads to a decrease in the ratio of the integrated intensities of the bands of the first and second positive systems with an increase in the energy of electrons that precipitate into the atmosphere. [ABSTRACT FROM AUTHOR]

Denitrification and anaerobic ammonium oxidation (anammox) are important biological processes of the nitrogen cycle that help to preserve the global ecosystem. However, indiscriminate development and global population growth result in the discharge of large amounts of nitrogen species (e.g., via the Haber–Bosch process), particularly nitrogen oxides and ammonia, which cannot be fully digested by microorganisms and therefore accumulate in soil and water. Photocatalysts can promote the conversion of nitrogen oxides and ammonia to molecular nitrogen under the action of photogenerated electrons and holes, thus mimicking denitrifying and anammox bacteria, respectively. Herein, we review the biomimetic photocatalysts and photoelectrochemical cells used to convert aqueous and airborne nitrogen species to molecular nitrogen and shed light on the charge transfer mechanism that should be selectively controlled to favor the formation of molecular nitrogen over that of nitrogen-containing intermediates and by-products. Last but not least, we discuss the outlooks and perspectives of solar-powered molecular nitrogen recovery and suggest guidelines for the design of high-performance denitrification/anammox bacteria-like photocatalysts. [ABSTRACT FROM AUTHOR]

We applied the Mayer group expansion method for solids to predict locations of the polymorphic phase transitions lines between molecular ɛ and ζ phases, as well as between molecular ζ phase and polymeric cubic-gauche-phase in highly compressed nitrogen solid. A simple potential model is proposed and its parameters are determined using known ab initio energy calculations for the molecular α phase. The results are compared with existing experimental data and the influence of intermolecular correlations on the temperature dependence of phase transition pressures is estimated. [ABSTRACT FROM AUTHOR]

The structures and energetic effects of molecular nitrogen adsorbates on nickel clusters are investigated using an extended Hückel model coupled with two models of the adsorbate–nickel interaction. The potential parameters for the adsorbates are chosen to mimic experimental information about the binding strength of nitrogen on both cluster and bulk surface phases of nickel. The first model potential is a simple Lennard-Jones interaction that leads to binding sites in holes defined by sets of near-neighbor nickel atoms. The second model potential has a simple three-body form that forces the model nitrogen adsorbates to bind directly to single nickel atoms. Significant rearrangement of the core nickel structures are found in both models. A disconnectivity graph analysis of the potential energy surfaces implies that the rearrangements arise from low transition state barriers and the small differences between available isomers in the nickel core. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nitrogen fixation is industrially realized by mass production of ammonia, the principal intermediate nitrogen source for N‐containing organic molecules. Instead, direct C−N bond formation from dinitrogen (N2) is of great interest but remains a challenge. Here, by virtue of unique plasma–liquid interactions, we developed an environmentally benign one‐pot approach to directly couple benzene and N2, two naturally abundant yet chemically inert molecules, into value‐added arylamines. Under the optimal conditions, an amination yield of 45 % was rapidly achieved, far better than the reported benzene amination efficiency using ammonia. A tentative reaction mechanism was proposed involving the long‐lived N2 (A3Σu+) and N2+ species, as evidenced by the key intermediates detected. With a deeper mechanistic understanding and by further optimizing the plasma reactor, the realization of cost‐effective electrical amination of benzene with N2 could become reality. [ABSTRACT FROM AUTHOR]

Nitrogen fixation is industrially realized by mass production of ammonia, the principal intermediate nitrogen source for N‐containing organic molecules. Instead, direct C−N bond formation from dinitrogen (N2) is of great interest but remains a challenge. Here, by virtue of unique plasma–liquid interactions, we developed an environmentally benign one‐pot approach to directly couple benzene and N2, two naturally abundant yet chemically inert molecules, into value‐added arylamines. Under the optimal conditions, an amination yield of 45 % was rapidly achieved, far better than the reported benzene amination efficiency using ammonia. A tentative reaction mechanism was proposed involving the long‐lived N2 (A3Σu+) and N2+ species, as evidenced by the key intermediates detected. With a deeper mechanistic understanding and by further optimizing the plasma reactor, the realization of cost‐effective electrical amination of benzene with N2 could become reality. [ABSTRACT FROM AUTHOR]

Cutting-edge research on graphite-like carbon nitride-based (g-C3N4) photocatalytic systems for molecular nitrogen fixation is summarized. The properties of modified g-C3N4 with grafted functional groups, structural defects (nitrogen or carbon vacancies), doped with nonmetals and metals, as well as g-C3N4-based binary and ternary composites with the participation of metals, their oxides, metalates, carbonates, hydrocarbons, and sulfides are discussed. The most promising areas of further research are outlined. [ABSTRACT FROM AUTHOR]

We model the (v′ = 1, v″ = 0) band of the Birge–Hopfield I band system of molecular nitrogen, N2, i.e. , emitted by nonthermal gas discharges in low pressure air. In particular, we calculate the rate of electron impact excitation of N2, which is thermally equilibrated at room temperature, to rotational levels J′ < 31 of N2(b1Πu, v′ = 1, J′). Subsequently, we calculate the intensity of emission lines resulting from radiative transitions from the aforementioned rotational levels to. Predissociation is the only nonradiative channel considered for the decay of N2(b1Πu, v′ = 1, J′) levels. [ABSTRACT FROM AUTHOR]

We model emissions from the Carroll-Yoshino (v′ = 0, v″ = 0) band of molecular nitrogen N2, i.e. due to nonthermal gas discharges in low pressure air and N2. In particular, we calculate the rate of excitation of thermally equilibriated N2 at room temperature (i.e. 300 K) to various rotational levels J′ of. Subsequently, we calculate the intensity of 47 emission lines resulting from radiative transitions from the aforementioned rotational levels. It is assumed that predissociation is the only nonradiative channel for the decay of excited levels. [ABSTRACT FROM AUTHOR]

The transformation of molecular nitrogen to a single-bonded atomic nitrogen is of significant interest from a fundamental stand point and because it is the most energetic non-nuclear material predicted. We performed an x-ray diffraction of nitrogen at pressures up to 170 GPa. At 60 GPa, we found a transition from the rhombohedral (R3c) ε-N2 phase to the ζ-N2 phase, which we identified as orthorhombic with space group P2221 and with four molecules per unit cell. This transition is accompanied by increasing intramolecular and decreasing intermolecular distances. The major transformation of this diatomic phase into the single-bonded (polymeric) phase, recently determined to have the cubic gauche structure (cg-N), proceeds as a first-order transition with a volume change of 22%. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) has been used to investigate molecular nitrogen and isolated nitrogen acceptors in single crystals of ZnO. These samples were grown by the seeded chemical vapor transport method with N[sub 2] added to the gas stream. A five-line EPR spectrum is observed at low temperature in the as-grown bulk crystals and is assigned to N[sup -, sub 2] molecules substituting for oxygen. This structure arises from nearly equal hyperfine interactions with two nitrogen nuclei ([sup 14]N, 99.63% abundant, I = 1). The spin Hamiltonian parameters for the N[sup -, sub 2] center are g[sub ] = 2.0036, g[sub ⊥] = 1.9935, A[sub ⊥] = 9.8 MHz, and A[sub ⊥] = 20.1 MHz, with the unique directions parallel to the c axis. Laser excitation at 9 K, with 325 or 442 nm light, eliminates the N[sup -, sub 2] spectrum (when the N[sup -, sub 2] convert to N[sup 0, sub 2]) and independently introduces the EPR spectrum due to isolated nitrogen acceptors (when N[sup -] acceptors convert to N[sup 0]). Removing the laser light and warming to approximately 100 K restores the crystal to its preilluminated state. In separate experiments, heating between 600 and 800 °C increases the number of N[sup -, sub 2] and N[sup 0] acceptors that can be observed. We suggest that the activation of these nitrogen acceptors occurs when complexes of hydrogen and nitrogen thermally dissociate. Further heating above 800 °C drives the two nitrogen acceptors to inactive forms. [ABSTRACT FROM AUTHOR]

Based on a modified numerical model of the ionosphere and plasmasphere developed at the Institute of Solar–Terrestrial Physics (ISTP), Siberian Branch, Russian Academy of Sciences, the altitude profiles of the Ne electron density for the quiet and disturbed states of the thermosphere were calculated for the conditions of January 25, 2009, at a geographical point with the coordinates 52.4° N, 104.3° E (Irkutsk). The disturbed conditions were set by varying the temperature of neutral particles T in the thermosphere. At altitudes below 180 km and above 250 km, with an increase/decrease in T, an increase/decrease in Ne occurs. At altitudes of 180–250 km, the opposite picture is observed: an increase/decrease in T causes a decrease/increase in Ne. The opposite nature of the change in the Ne profile is associated with the influence of the ratio of concentrations of atomic oxygen and molecular nitrogen [O]/[N2] at the altitudes of region F. Quantitative estimates of the change in Ne at different altitudes with changes in the temperature of neutral particles were obtained. It has been established that a change in T by 1 K leads to a change in Ne by 0.2–0.3%. The modeling results are compared with observations of the peak electron density NmF2 obtained on the Irkutsk ionosonde during sudden stratospheric warming in January 2009. [ABSTRACT FROM AUTHOR]

Great enhancement of molecular nitrogen luminescence in the afterglow of nitrogen-helium gas mixtures was observed at temperatures ≤ 10 K. The effect is explained by the increased efficiency of the recombination of nitrogen atoms and energy transfer from metastable nitrogen molecules and helium atoms to nitrogen molecules in the cold dense helium vapor. [ABSTRACT FROM AUTHOR]

Highly excited states of gerade symmetry in molecular nitrogen have been investigated in a resonance-enhanced XUV+Vis (extreme ultraviolet+visible) transition scheme. Nineteen bands have been observed, of which only four involve known states [k [sup 1]...[sub g] (v = 1), x [sup l]&Zigma;[sup -, sub g] (v = 2), and [sup 1]... (v = 1,2)], albeit in new systems. Three of the newly observed states have been assigned as y[sup 1]...[sup g, sub g] (v = 3) and k [sup l]...[sub g] (v = 2,3). Level energies are determined with an accuracy of ≈0.20 cm[sup -1]. [ABSTRACT FROM AUTHOR]

A healthy breath is mainly composed of water, carbon dioxide, molecular nitrogen, and oxygen and it contains many species, in small quantities, which are related to the ambient atmosphere and the metabolism. The breath of a person affected by lung cancer presents a concentration of 1-propanol higher than usual. In this context, the development of specific sensors to detect 1-propanol from breath is of high interest. The amount of propanol usually detected on the breath is of few ppb; this small quantity is a handicap for a reliable diagnostic. This limitation can be overcome if the sensor is equipped with a pre-concentrator. Our studies aim to provide an efficient material playing this role. This will contribute to the development of reliable and easy to use lung cancer detectors. For this, we investigate the properties of a few hydrophobic porous materials (chabazite, silicalite-1, and dealuminated faujasite). Hydrophobic structures are used to avoid saturation of materials by the water present in the exhaled breath. Our experimental and simulation results suggest that silicalite −1 (MFI) is the most suitable structure to be used as a pre-concentrator. [ABSTRACT FROM AUTHOR]

The absolute population of the B3Πg state of molecular nitrogen is calculated from the intensity of electron-vibrational bands of the first positive system. The absolute population of the metastable A3Σu state of nitrogen molecules is calculated based on the solution of the balance equation. It is established that the population of the metastable state of molecular nitrogen increases with a decrease in the pressure and increase in the current intensity of the glow discharge. The results of determining the population of the A3Σu state of nitrogen molecules under conditions of simultaneous excitation of glow and vacuum arc discharges are presented. [ABSTRACT FROM AUTHOR]

A comprehensive study of electron collisions with the X1Σg+ ground state as well as the metastable A3Σu+ and a1Πg excited states of the N2 molecule is reported using the fixed-nucleus R-matrix method. Integral elastic scattering and electronic excitation cross sections from the X1Σg+ ground state to the eight lowest electronic states, A3Σu+, B3Πg, W3Δu, B′3Σu−, a1Πg, a′1Σu−, w1Δu and C3Πu, overall agree well with the available experimental and theoretical results although updates of some recommended values are suggested. Accurate electron impact electronic transition cross sections starting from the A3Σu+ and a1Πg metastable excited states are reported. The total summed electronic transition cross sections from the a1Πg state is dominant: an order of magnitude higher than those of the X1Σg+ ground state. The de-excitation cross sections generally show a downward trend with increasing incident electron energy, which is different from the elastic and electronic excitation cross sections which generally increase with collision energy. There is a prominent 2Πu symmetry resonance peak at 2.8 eV for electronic de-excitation scattering of a1Πg → B3Πg, which significantly contributes to the total summed cross sections from the a1Πg excited state. The present results provide a new insight which will aid understanding of electron spectra in the atmosphere of the Earth and Titan. [ABSTRACT FROM AUTHOR]