Nitrogen Molecules N2 Research Articles

Review on the QM/MM Methodologies and Their Application to Metalloproteins.

The multiscaling quantum mechanics/molecular mechanics (QM/MM) approach was introduced in 1976, while the extensive acceptance of this methodology started in the 1990s. The combination of QM/MM approach with molecular dynamics (MD) simulation, otherwise known as the QM/MM/MD approach, is a powerful and promising tool for the investigation of chemical reactions’ mechanism of complex molecular systems, drug delivery, properties of molecular devices, organic electronics, etc. In the present review, the main methodologies in the multiscaling approaches, i.e., density functional theory (DFT), semiempirical methodologies (SE), MD simulations, MM, and their new advances are discussed in short. Then, a review on calculations and reactions on metalloproteins is presented, where particular attention is given to nitrogenase that catalyzes the conversion of atmospheric nitrogen molecules N₂ into NH₃ through the process known as nitrogen fixation and the FeMo-cofactor.

Zero-dimensional and pseudo-one-dimensional models of atmospheric-pressure plasma jets in binary and ternary mixtures of oxygen and nitrogen with helium background

A zero-dimensional (volume-averaged) and a pseudo-one-dimensional plug-flow (spatially resolved) model are developed to investigate atmospheric-pressure plasma jets operated with He, He/O2, He/N2 and He/N2/O2 mixtures. The models are coupled with the Boltzmann equation under the two-term approximation to self-consistently calculate the electron energy distribution function. An agreement is obtained between the zero-dimensional model calculations and the spatially averaged values of the plug-flow simulation results. The zero-dimensional model calculations are verified against spatially resolved simulation results and validated against a wide variety of measurement data from the literature. The nitric oxide (NO) concentration is thoroughly characterized for a variation of the gas mixture ratio, helium flow rate and absorbed power. An ‘effective’ and a hypothetical larger rate coefficient value for the reactive quenching are used to estimate the role of the species N2(A3Σ, B3Π; v > 0) and multiple higher N2 electronically excited states instead of only N2(A3Σ, B3Π; v = 0) in this quenching. The NO concentration measurements at low power are better and almost identically captured by the simulations using the ‘effective’ and hypothetical values, respectively. Furthermore, the density measurements under the same operation conditions are also better predicted by the simulations adopting these values. It is found that the contribution of the vibrationally excited nitrogen molecules N2(v ⩾ 13) to the net NO formation rate gains more significance at higher power. The vibrational distribution functions (VDFs) of molecular oxygen O2(v < 41) and nitrogen N2(v < 58) are investigated regarding their formation mechanisms and their responses to the variation of operation parameters. It is observed that the N2 VDF shows a stronger response than the O2 VDF. The sensitivity of the simulation results with respect to a variation of the VDF resolutions, wall reaction probabilities and synthetic air impurity levels is presented. The simulated plasma properties are sensitive to the variation, especially for a feed gas mixture containing nitrogen. The plug-flow model is validated against one-dimensional experimental data in the gas flow direction, and it is only used in case an analysis of the spatially resolved plasma properties inside the jet chamber is of interest. The increasing NO spatial concentration in the gas flow direction is saturated at a relatively high power. A stationary O2 VDF is obtained along the direction of the mass flow, while a continuously growing N2 VDF is observed until the jet nozzle.

N2 dissociation and kinetics of N(4S) atoms in nitrogen DC glow discharge

N2 dissociation in pure nitrogen plasma has a long history of research. It seems to be a complex process which comprises many reactions involving various electronic and vibrational nitrogen states whose contributions can vary depending on conditions. In this paper, we studied N2 dissociation in the stationary N2 discharge both experimentally and theoretically. We used a DC glow discharge in a quartz tube in pure N2 at moderate pressures (5–50 Torr). The degree of dissociation, atomic nitrogen loss rate and gas temperature were measured by applying optical emission spectroscopy (OES) and as a result an ‘effective’ rate constant for nitrogen dissociation was obtained across a wide range of the reduced field E/N. The analysis of N2 dissociation was carried out using a specially developed 1D radial self-consistent model which takes into account the spatial inhomogeneities of species concentrations, E/N, electron energy distribution function, Tgas etc, together with fairly complete plasma-chemical kinetics and all the cross-sections known to date for electron kinetics. The model was successfully validated through the experimental results obtained for electric field, gas temperature and N atom density. Comprehensive analysis of closely coupled processes in nitrogen plasmas—gas heating, VDF formation and N2 dissociation—was carried out. Simulations reproduced the experimental data on well and allowed us to evaluate the different contributions of the various dissociation channels considered. It was shown that the nitrogen dissociation mechanism in the stationary N2 discharge is provided by direct electron impact via the excitation of the pre-dissociative states from the vibrationally excited nitrogen molecules N2(X, υ). The upper limit for the rate constant of the processes N2(A) + N2(14 ⩽ υ ⩽ 19) → N + N + N2 was estimated to be 5 · 10−14 cm3 s−1.

Inelastic collisions of molecules within the SFO model

An inelastic collision of diatomic molecule AB with structureless particle M (VT energy exchange) is considered within the SFO/SFHO model. An approach for determining the energy efficiency of excitation of molecular vibrational levels, energy-loss matrix, and total energy loss in a head-on collision with molecules/atoms is proposed. Nitrogen molecules N2 are chosen as AB and M. An interaction in the AB–M system is described using the “improved” Lennard-Jones potential.

The rate constant of diatomic molecule dissociation within the shock forced oscillator model (SFO model)

A numerical analytical investigation of the shock forced oscillator (SFO) model as applied to the “diatomic molecule AB-structureless particle M” system is continued. The SFO model is based on the quantum theory of strong perturbations and allows one to estimate probabilities Wi→f for the transitions from level i to level f of diatomic molecule AB. The numerical analysis was carried out by the example of the nitrogen molecule N2, with anharmonic description of the internuclear interaction potential. The intermolecular interaction potentials in the N2-N2 system are numerically analyzed using the Morse potential, the classical Lennard-Jones potential, and the “improved” Lennard-Jones potential.

Emission properties of an atmospheric-pressure helium plasma jet generated by a barrier discharge

The emission properties of an atmospheric-pressure helium plasma jet generated by a barrier discharge in a capillary blown with helium are studied. The spectral composition of the radiation of the studied plasma jet and the spatial-spectral distribution of its intensity are investigated in detail. It is shown that the emission spectrum of the generated plasma jet outside the capillary consists mainly of electronic-vibrational transitions of the first negative system of ionized nitrogen molecules N2+(B2Σu+ → X2Σg+) and the second positive system of neutral nitrogen molecules N2(C3Πu → B3Πg).

キシレンによるN2(A3&Sigma;u+)の失活とキシレン分解生成物の陰極表面への付着による電流阻止作用

The collisional quenching rate coefficient of metastable nitrogen molecules N2(A3Σu+) by m-xylene (C8H10) is determined experimentally in the Townsend discharge. The diffusion coefficient of N2(A3Σu+), and the reflection coefficient of N2(A3Σu+) at the electrode surface are also determined simultaneously. During the experiment, we find that it is difficult to continue the current measurement necessary to determine the fundamental constants of N2(A3Σu+) for long period. It is considered that any by-product of xylene would be decomposed by N2(A3Σu+) is deposited on the cathode, through repeated experiments, then the current-voltage curves consistently shift to the higher-E/p0 region. For the purpose of clarifying the reason behind this behavior, we confirm that these changes are caused by the current prevention by the decreases of initial photoemission current from the cathode and the decrease in the secondary ionization coefficient γ, because the cathode surface is covered by deposition film of a by-product of decomposed xylene.

Air‐density‐dependent model for analysis of air heating associated with streamers, leaders, and transient luminous events

Blue and gigantic jets are transient luminous events in the middle atmosphere that form when conventional lightning leaders escape upward from the thundercloud. The conditions in the Earth's atmosphere (i.e., air density, reduced electric field, etc.) leading to conversion of hot leader channels driven by thermal ionization near cloud tops to nonthermal streamer forms observed at higher altitudes are not understood at present. This paper presents a formulation of a streamer‐to‐spark transition model that allows studies of gas dynamics and chemical kinetics involved in heating of air in streamer channels for a given air density N under assumption of constant applied electric field E. The model accounts for the dynamic expansion of the heated air in the streamer channel and resultant effects of E/N variations on plasma kinetics, the vibrational excitation of nitrogen molecules N2(v), effects of gains in electron energy in collisions with N2(v), and associative ionization processes involving N2(A3Σu+) and N2(a′1Σu−) species. The results are in excellent agreement with available experimental data at ground and near‐ground air pressures and demonstrate that for the air densities corresponding to 0–70 km altitudes the kinetic effects lead to a significant acceleration of the heating, with effective heating times scaling closer to 1/N than to 1/N2 predicted on the basis of similarity laws for Joule heating. This acceleration is attributed to a strong reduction in electron losses due to three‐body attachment and electron‐ion recombination processes with reduction of air pressure.

Detection of metastable excited molecules N2(A3Σu+) in an atmospheric pressure nitrogen discharge by Raman scattering

AbstractRaman scattering from metastable excited nitrogen molecules N2(A3Σu+) created by an impulse discharge in nitrogen at atmospheric pressure was detected. A pulsed Nd:YAG laser at a wavelength of 266 nm was used as the light source, and Raman scattering from N2(A3Σu+) at a wavelength of 277 nm was detected using an interference filter and photomultiplier tube. The filter had sufficient rejection of Rayleigh scattering of laser light at a wavelength of 266 nm and of Raman scattering from ground‐state nitrogen molecules N2(X1Σg+) at a wavelength of 284 nm. The temporal variation of the signal intensity of Raman scattering from N2(A3Σu+) was measured by transmitting the laser light at different time delays relative to sparkover. The results showed that the signal intensity decayed with a time constant of about 200µs. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(6): 34–40, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10205

ラマン散乱法による大気圧窒素放電中の準安定励起分子N&lt;sub&gt;2&lt;/sub&gt;(A&lt;sup&gt;3&lt;/sup&gt;&amp;Sigma;&lt;sub&gt;u&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;)の検出

Raman scattering from metastable excited nitrogen molecules N2(A3Σu+) created by an impulse discharge in nitrogen at atmospheric pressure was detected. A pulsed Nd:YAG laser of wavelength 266 nm was used as the light source, and Raman scattering from N2(A3Σu+) at wavelength 277 nm was detected using an interference filter and photomultiplier tube. The filter had sufficient rejection of Rayleigh scattering of laser light at wavelength 266 nm and Raman scattering from ground state nitrogen molecules N2(X1Σg+) at wavelength 284 nm. The temporal variation of the signal intensity of Raman scattering from N2(A3Σu+) was measured by transmitting the laser at different time delays relative to sparkover. Results showed that the signal intensity decayed with a time constant of about 200 μs.

Ionization current in N2 gas: XI. three-dimensional analysis for loss processes of metastable particles affected by the reflection at the boundary

Loss of the metastable nitrogen molecule N2(A3Σ+u) in plane parallel electrodes has been investigated by us previously by solving the diffusion equation. Our procedure is based on an analysis using the third kind of boundary condition, which can take account of finite values for the density of N2(A3Σ+u) at the electrode surfaces. The values of the effective lifetime of N2(A3Σ+u) calculated from this analysis were reasonably consistent with our experiments. This paper describes the behavior of the effective lifetimes of RN2(A3Σ+u) in a cylindrical cavity. The analytical treatment of the diffusion equation for N2(A3Σ+u) proposed by us is extended to three-dimensional space. We systematically report the effective lifetimes of metastable molecules in a cylindrical cavity. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 1–8, 2000

Two-dimensional orientational motion as a multichannel reaction by computer simulation

The orientational diffusion of a nitrogen molecule N2 in a three-dimensional crystal of argon atoms is studied by using the reaction coordinate formalism and the Bennett–Chandler approach. To study the two-dimensional orientational diffusion the reaction coordinate formalism has to be generalized to multichannel reactions. The rate coefficient for the motion between the six stable orientational states is determined from correlation function expressions, which include corrections to transition-state theory due to recrossings of free energy barriers. At high temperatures the simulation results are compared with results obtained by standard molecular dynamics methods. At low temperatures the transmission coefficient is computed and the dependence of the plateau value upon the density of the surrounding argon matrix and upon the isotopes, chosen to form the N2 molecule, is investigated.

Electron-impact vibrational relaxation in high-temperature nitrogen

Vibrational relaxation process of N2 molecules by electron-impact is examined for the future planetary entry environments. Multiple-quantum transitions from excited states to higher/lower states are considered for the electronic ground state of the nitrogen molecule N2(X1 S+). Vibrational excitation and de-excitation rate coefficients obtained by computational quantum chemistry are incorporated into the diffusion model to evaluate the time variations of Vibrational number densities of each energy state and total vibrational energy. Results show a nonBoltzmann distribution of number densities at the earlier stage of relaxation, which in turn suppresses the equilibration process, but affects little on the time variation of total vibrational energy. An approximate rate equation and a corresponding relaxation time from the excited states, compatible with the system of flow conservation equations, are derived for the first time. The relaxation time from the excited states indicates the weak dependency of the initial vibrational temperature, and is shorter than the previously obtained relaxation time in which only excitation from the ground state was considered. The empirical curve-fit formulas for the improved e-V relaxation time is obtained. The rate equation and the relaxation time, suited for the numerical simulation of the highly ionized planetary entry flowfields, are suggested.

Rate constants for deactivation of N2* (A3Σu+, nu =0, 1) by H and D atoms

The quenching reactions of metastable nitrogen molecules N2*(A3 Sigma u+, nu =0, 1) with atomic hydrogen and atomic deuterium have been studied in a room-temperature discharge flow system by monitoring the time decay of the 0, 6 and 1, 10 emissions of the Vegard-Kaplan (N2*(A3 Sigma u+) to N2(X1 Sigma g+)) band. Rate constants, kQ, of (1.3+or-0.4)*10-10 and (0.90+or-0.12)*10-10 cm3 s-1 were measured for Q=H, nu =0, 1 and (1.0+or-0.3)*10-10 and (0.68+or-0.04)*10-10 cm3 s-1 for Q=D, nu =0, 1, with an accuracy of 90%. NO gas was used as a tracer for N2*(A3). KQ values of (1.0+or-0.1)*10-10 cm3 s-1 for Q=H and (0.94+or-0.14)*10-10 cm3 s-1 for Q=D were obtained for the mixture of N2*(A3, nu =0) and N2*(A3, nu =1).

DETERMINATION OF DIFFUSION COEFFICIENT AND QUENCHING RATE COEFFICIENT OF METASTABLE N2 MOLECULES N2(A3∑u+) USING TOWNSEND DISCHARGING

The diffusion coefficient Dm and quenching rate coefficient Kq of metastable nitrogen molecule N2(A3∑u+) in pure N2 has been determined using Townsend dischaging. The values of Dm of 128 cm2/s and KN2 of 8.1×10-19 cm3/s were obtained respectively.

Study on the State of Nitrogen Adsorbed on Evaporated Barium Film

In order to clarify the nature of activated adsorption, the adsorption of nitrogen on the freshly evaporated barium film, the replacement of the adsorbed nitrogen by oxygen and the liberation of the nitrogen by means of electron impacts were studied. Immediately after the adsorption a portion of the activated adsorbed nitrogen is bound loosely to the surface of barium, and is gradually converted to a state of firmer binding which is similar to that involved in chemical reaction. The loosely bound nitrogen was ascertained to be in molecular state, and that its electronic configuration is not much perturbed from the ground state of nitrogen X1Σg+. The existence of ionized nitrogen molecule N2+(2Σg+) on the metal surface was suggested.