Search

The process of oxidation of molecular nitrogen by high-energy oxidants, such as nitric acid vapor, products of the thermolysis of nitric acid, and hydrogen peroxide, in a cold plasma stream was studied. To implement the process of obtaining nitric acid from atmospheric air using reproductive technology (Zakharov's method), the design of a reactor for obtaining nitrogen oxides by direct oxidation of nitrogen in a cold plasma stream is proposed. At the same time, it was proposed to use the effect of obtaining nitrogen oxides in an air mixture with nitric acid vapors (the Karavaev effect) and during the thermal decomposition of hydrogen peroxide with atmospheric nitrogen (the Nagiev effect). The effectiveness of the use of cold plasma for the oxidation of atmospheric nitrogen was established, which is confirmed by the obtained dependences. It is shown that the amount of nitrogen oxides that are formed depends on the efficiency of the formation of a stable flow of OH- radicals in the plasma flow. It was also found that the amount of nitrogen oxides depends on the parameters of the plasma generator, the composition of the liquid used in the burner, and the amount of air supplied. The effect of nitric acid, hydrogen peroxide, and alcohols as activators of atmospheric nitrogen oxidation in a high-energy field was revealed. It was determined that when comparing three activator substances, which are able to form OH- radicals during their decomposition, it is hydrogen peroxide that is the most promising activator substance for carrying out the process of atmospheric nitrogen oxidation in the plasma flow. The amount of nitrogen oxides formed in the cold plasma region is almost independent of the flow rate of the reaction mixture through the reactor and remains almost unchanged in a wide range of changes in flow rates from 30 to 3000 l/h. [ABSTRACT FROM AUTHOR]

The emission spectra of a streamer discharge in pure nitrogen provide an important tool for investigating the fundamental kinetics of excited electronic states of N2 and benchmark data for validating advanced kinetic schemes for numerical models. In this work, we characterize a streamer monofilament developed in a dielectric barrier discharge configuration, including electrical characteristics, time-resolved images and N2/N 2 + emission spectra, all acquired with nanosecond temporal resolution. Time-resolved images and emission characteristics provide clear evidence of the formation of a cathode-directed streamer and allow determining the streamer propagation velocity and the typical E / N values using the intensity ratio of nitrogen spectral bands in the center of the discharge gap. We also measure the vibrational distributions of the N2(C 3 Π u , v = 0–4) and N 2 + (B 2 Σ u + , v = 0–2) states. The population of N2(C 3 Π u , v = 0–4) state, initially formed by energetic electrons in the streamer head, changes later significantly due to the decrease in the mean energy and concentration of the streamer channel electrons. After a few tens of nanoseconds, the electron-impact excitation rate of N2(C 3 Π u ) becomes negligible compared to its population by the N2( A 3 Σ u + ) + N2( A 3 Σ u + ) pooling. The experimental findings are supported and consistent with the 0D state-to-state kinetic model results and reveal the participation of high vibrational levels of N2( A 3 Σ u + ) in the pooling reactions. [ABSTRACT FROM AUTHOR]

The mechanisms of the production of vibrationally excited NO and N2 molecules at the altitudes of the middle atmosphere of the Earth during high‐energetic proton precipitation on 20 January 2005 are considered. The study of vibrational populations N2(X1Σg+,v′ > 0) during high‐energetic proton precipitation has shown different principal mechanisms in the N2(X1Σg+,v′ > 0) excitation. First, the excitation by secondary electrons is principal for vibrational levels v′ = 1−10. Second, it is obtained that intramolecular electron energy transfer process in N2(A3Σu+)+N2 collisions dominates in vibrational excitation of high vibrational levels v′ = 20−30. It is shown that the chemical reaction of metastable atomic nitrogen with molecular oxygen is the main production mechanism of vibrationally excited NO(X2Π,v > 0) and of the radiation of 5.3 and 2.7 μm infrared emissions at these altitudes. The calculated intensities of the 5.3 μm emission are compared with experimental data from SABER instrument on TIMED spacecraft received at the time of the proton precipitation. The role of VV′‐processes in the radiation of 5.3 μm infrared emission is discussed. Plain Language Summary: The Ground Level Enhancement on 20 January 2005 is the strongest event of precipitation of energetic protons in the Earth's atmosphere. We study molecular processes at the altitudes of the middle atmosphere during the precipitation. Special attention is paid to a modeling of vibrational kinetics of molecular nitrogen N2 and nitric oxide NO. The influence of electronically excited states of N2 and NO molecules on the vibrational kinetics is considered. The intensities of NO 5.3 and 2.7 μm infrared emissions are calculated. The calculated intensities of the 5.3 μm emission are compared with experimental data from SABER instrument on TIMED spacecraft received at the time of the proton precipitation. Key Points: Vibrational kinetics of NO and N2 in the middle atmosphere during high‐energetic proton precipitation is consideredIntramolecular and intermolecular electron energy transfers are taken into account in calculations of vibrational populations of moleculesIt is shown that there is a dependence of calculated vibrational populations on atmospheric altitude [ABSTRACT FROM AUTHOR]

Generation of coherent extreme ultraviolet (XUV) pulses is a nonlinear process of high harmonic generation (HHG). HHG produced in molecular nitrogen (N2) medium has been obtained using ultrashort intense laser pulses. The strong laser field was focused onto a gas cell to produce short wavelengths having photon energy up to 54 eV. The highest photon energy is experimentally observed as the 35th order. The absorption of harmonics restricts the harmonic yield efficiency. The harmonic yield is affected by the interaction length and medium pressure. The harmonic yield changes with the medium parameters. The simulation for the absorption length was performed using the Mathematica program. Variation of the harmonic signal has been attributed to the absorption of harmonics, and it is compared with the absorption length.

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]

Generation of coherent extreme ultraviolet (XUV) pulses is a nonlinear process of high harmonic generation (HHG). HHG produced in molecular nitrogen (N2) medium has been obtained using ultrashort intense laser pulses. The strong laser field was focused onto a gas cell to produce short wavelengths having photon energy up to 54 eV. The highest photon energy is experimentally observed as the 35th order. The absorption of harmonics restricts the harmonic yield efficiency. The harmonic yield is affected by the interaction length and medium pressure. The harmonic yield changes with the medium parameters. The simulation for the absorption length was performed using the Mathematica program. Variation of the harmonic signal has been attributed to the absorption of harmonics, and it is compared with the absorption length. [ABSTRACT FROM AUTHOR]

Even though natural sources of air pollution account for over 50% of sulphur compounds, 93% of nitrogen oxide which are the most dangerous artificial anthropogenic sources of air pollution and primarily associated with the combustion of fossil fuel. Coal-fired thermal power plants and industrial fuel-burning plants that emit large quantities of nitrogen oxides (NO and NO2), solids (ash, dust, soot), as well as carbon oxides, aldehydes, organic acids into the atmosphere pollute the environment in majority. In the present work, a mathematical model and a scheme for calculating the formation of nitrogen oxide has been developed. Also, the dependence of the rate of release of fuel nitrogen from coal particles at the initial stage of gasification and content of volatiles has been obtained. The main regularities of the formation of NOx at the initial section of the flame in the ignition zone of the swirl burner flame during the combustion of Ekibastuz coal have been revealed. Modern environmental requirements for the modernization of existing and the creation of new heat and power facilities determine the exceptional relevance of the development of effective methods and constructions to reduce emissions of nitrogen oxides, sulfur oxides and ash to 200, 300, and 100 mg/nm³ at α = 1.4. The dust consumption in all experiments was kept constant and amounted to 0.042 g/s, as well as with the results of calculating the thermal decomposition of the Ekibastuz coal dust, the recombination of atomic nitrogen into nitrogen molecules, and the kinetics of the formation of fuel nitric oxide. It was found that despite the presence of oxygen in Ekibastuz coal for gases Odaf = 11.8 % in an inert atmosphere, nitrogen oxides are not formed. [ABSTRACT FROM AUTHOR]

TIMED/GUVI limb measurements and first‐principles simulations from the Thermosphere Ionosphere Electrodynamics Global Circulation Model (TIEGCM) are used to investigate thermospheric atomic oxygen (O) and molecular nitrogen (N2) responses in the middle thermosphere on a constant pressure surface (∼160 km) to the November 20 and 21, 2003 superstorm. The consistency between GUVI observations and TIEGCM simulated composition changes allows us to utilize TIEGCM outputs to investigate the storm‐time behaviors of O and N2 systematically. Diagnostic analysis shows that horizontal and vertical advection are the two main processes that determine the storm‐induced perturbations in the middle thermosphere. Molecular diffusion has a relatively smaller magnitude than the two advection processes, acting to compensate for the changes caused by the transport partly. Contributions from chemistry and eddy diffusion are negligible. During the storm initial and main phases, composition variations at high latitudes are determined by both horizontal and vertical advection. At middle‐low latitudes, horizontal advection is the main driver for the composition changes where O mass mixing ratio Ψo decreases (N2 mass mixing ratio ΨN2 increases); whereas horizontal and vertical advection combined to dominate the changes in the regions where Ψo increases (ΨN2 decreases). Over the entire storm period, horizontal advection plays a significant role in transporting high‐latitude composition perturbations globally. Our results also demonstrate that storm‐time temperature changes are not the direct cause of the composition perturbations on constant pressure surfaces. Key Points: Horizontal and vertical advection are the two main processes driving O and N2 changes in the middle thermosphere during the superstormMolecular diffusion is relatively weak in the middle thermosphere, acting to compensate for O and N2 changes caused by transport processesStorm‐time temperature changes are not the direct cause of the composition perturbations on constant pressure surfaces [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]

Electron detachment from O− is important for understanding of lightning‐induced upper atmospheric discharges. Contrary to previous studies, Rayment and Moruzzi (1978) (RM78) argue that the associative detachment reaction of O− with N2 proceeds with N2 in its ground state. Here, we analyze the experimental setup in RM78 and demonstrate that vibrationally excited N2 may have in fact contaminated the results, the theoretical approach in RM78 requires corrections, and the rate calculations provided in RM78 are inconsistent. As the vibrational temperature of N2 remains relatively low in the initial stages of gas discharges in air, i.e., streamer formation, we conclude that if in fact vibrationally excited N2 is required for the O− + N2 → N2O + e reaction to proceed, the process will happen only in later stages of the discharge, e.g., during streamer to leader transition. Controlled experiments are required to reconcile the literature on the reaction of O− with ground state N2. Plain Language Summary: The development of lightning induced transient luminous events in the middle atmosphere (i.e., sprite discharges) usually proceeds on very short time scales measured in milliseconds. The modeling of these discharges requires accounting for a set of relatively fast reactions, that includes the electron impact ionization of ambient oxygen and nitrogen molecules, the dissociative attachment of electrons and the electron impact excitation of electronic states of N2 that have relatively short lifetimes and are responsible for observed visible, infrared, and ultraviolet signatures of these events detected from various (orbital and ground based) remote sensing platforms. Here we discuss the existing knowledge on the associative detachment of electrons from O− ions obtained in previous current growth laboratory experiments under steady state conditions. This detachment process has been included in several recently published models of transient luminous events. This process may be applicable to later stages of discharge development when significant quantities of vibrationally excited nitrogen molecules accumulate. This work provides evidence that it may not be applicable during initiation of these discharges. Key Points: Applicability of the associative detachment of electrons from O− ions to modeling of lightning induced transient luminous events is discussedThe detachment rate obtained in previous steady state laboratory experiments requires correctionControlled experiments are required to reconcile the literature on the detachment reaction of O− with ground state N2 and vibrationally excited N2 [ABSTRACT FROM AUTHOR]

N2 is a major constituent of Earth and planetary atmospheres. First, evidenced in 1952, the dissociative photoionization of molecular nitrogen, N2, plays an important role in the species abundance, out of equilibrium evolution, and chemical reactivity of diverse media including upper atmospheres (the so-called ionospheres) and plasma. Many scenarios were proposed for rationalizing the dissociative ionization mechanisms and exit channels, which are reviewed here, mainly involving the N2+(C2∑u+, v+) vibrational levels state-to-state dynamics on which we focus. We show, however, that previous studies are not comprehensive enough for fully shedding light on the complex undergoing processes. As a complementary global work, we used state-of-the-art quantum chemistry, time dependent and independent theoretical approaches associated to advanced experimental techniques to study the unimolecular decomposition of the N2+ ions forming the N+ + N products. In addition to the already suggested spin-orbit-induced predissociation of the cationic C2∑u+ state, we documented a new mechanism based on vibronic coupling and tunneling dissociation. Besides, the quantum processes highlighted here should be also in action in the dynamics of electronically excited larger molecular systems involved in physical and chemical phenomena in plasma and in various natural environments on Earth and beyond.

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]

Ab initio calculations of the adiabatic potential curves and matrix elements of radial nonadiabatic coupling of the N2 molecule for the states related to dissociation limits I-V were performed. The most important spectral characteristics of the adiabatic states agreed well with the available experimental and theoretical data. The diabatic states were constructed. The diabatic quantum defects and radial matrix elements of the configuration interaction of the dissociative and Rydberg configurations whose states converge to the ground state X2Σg+ and the first electronically excited state A2Πu of the N2+ ion were calculated. The possibility of using the results for calculating the cross sections and rate constants of dissociative recombination and associative ionization within the framework of the multichannel quantum defect theory was discussed. [ABSTRACT FROM AUTHOR]

Four thermodynamic properties of pure N 2 and O 2 fluids were calculated over a continuous temperature range in the near-critical region employing molecular dynamics combined with the multistate Bennett acceptance ratio (MBAR) technique. The non-asymptotic critical anomalies of the isothermal compressibility, the thermal expansion coefficient and the heat capacities at constant pressure and constant volume were determined in the 0.80 T c –1.20 T c temperature range along the 1.00 P c and 1.15 P c isobars. A single-site united-atom model and a two-site rigid rotor force fields were used in the simulations. The results show that effective force fields developed to describe accurately the behavior of liquids and dense gases in general can be used to obtain near-critical anomalies of the thermodynamic properties. Furthermore, the computed values are in very good agreement with NIST data when available. The results fill existing gaps of the NIST database in the near-critical vicinity of the critical temperature along the critical isobar, especially for the heat capacities. The MBAR technique was crucial to describe the continuous and sharp peak of each property as functions of the temperature. The results indicated that even with a simple force field such as the united-atom one-site approach, very good results could be obtained for the non-asymptotic critical anomalies of thermodynamic properties without using renormalization group techniques. The computation of accurate results was possible due to the availability of precise critical constants especially for the simpler one-site force field. The inclusion of the anisotropy in the force field does not necessarily improve the computed thermodynamic properties in the near critical region. [ABSTRACT FROM AUTHOR]

We have examined the current state of research on photocatalytic systems for the reductive conversion of CO2 and N2 using various semiconductor nanomaterials with a discussion of the photocatalytic properties of individual and doped nanocrystalline semiconductors, their binary nanoheterostructures, and systems containing various sensitizers. The most promising directions are outlined for further research in this area of modern photochemistry. [ABSTRACT FROM AUTHOR]

We have examined the current state of research on photocatalytic systems for the reductive conversion of CO2 and N2 using various semiconductor nanomaterials with a discussion of the photocatalytic properties of individual and doped nanocrystalline semiconductors, their binary nanoheterostructures, and systems containing various sensitizers. The most promising directions are outlined for further research in this area of modern photochemistry. [ABSTRACT FROM AUTHOR]