Bands Of Molecular Nitrogen Research Articles

One-dimensional air temperature measurements by air resonance enhanced multiphoton Ionization thermometry (ART).

In this work, a detailed calibration study is performed to establish non-intrusive one-dimensional (1D) rovibrational temperature measurements in unseeded air, based on air resonance enhanced multiphoton ionization thermometry (ART). ART is generated by REMPI (resonance enhanced multi-photon ionization) of molecular oxygen and subsequent avalanche ionization of molecular nitrogen in a single laser pulse. ART signal, the fluorescence from the first negative band of molecular nitrogen, is directly proportional to the 2-photon transition of molecular oxygen C3Π (v = 2) ← X3Σ (v'=0), which is used to determine temperature. Experimentally, hyperfine structures of the O2 rotational branches with high temperature sensitivity are selectively excited through a frequency-doubled dye laser. Electron-avalanche ionization of N2 results in the fluorescence emissions from the first negative bands of N2 + near 390, 425, and 430nm, which are captured as a 1D line by a gated intensified camera. Post processing of the N2 + fluorescence yields a 1D thermometry line that is representative of the air temperature. It is demonstrated that the technique provides ART fluorescence of ∼5cm in length in the unseeded air, presenting an attractive thermometry solution for high-speed wind tunnels and other ground test facilities.

Air resonance enhanced multiphoton ionization tagging velocimetry.

Air resonance enhanced multiphoton ionization (REMPI) tagging velocimetry (ART) was demonstrated in quiescent and supersonic flows. The ART velocimetry method utilizes a wavelength tunable laser beam to resonantly ionize molecular oxygen in air and generate additional avalanche-type ionization of molecular nitrogen. The fluorescence emissions from the first negative and first positive bands of molecular nitrogen are, thus, produced and used for flow tagging. Detailed characterization of ART was conducted, including the effects of oxygen resonance to fluoresce nitrogen, nitrogen fluorescence spectrum, laser energy deposition into quiescent flow showing minimal perturbations in flow, fluorescence lifetime study at various pressures, and line tagging without breakdown. Pointwise velocity measurements within a supersonic flow from a nominal Mach 1.5 nozzle have been conducted and characterized.

Luminescence of Lyman–Birge–Hopfield Bands of N2 in the Earth’s Atmosphere during the Precipitation of High-Energy Electrons

The luminescence intensity profiles of Lyman–Birge–Hopfield bands of molecular nitrogen have been calculated for the precipitation into the Earth’s atmosphere of electrons with energies of 10 keV to 10 MeV. With an increase in the energy of electrons penetrating the atmosphere, there is an increase in the contribution of the quenching of the a1Πg N2 state in molecular collisions. This leads to a reduced ratio of the integral luminescence intensities of the Lyman–Birge–Hopfield ultraviolet bands and the second positive system upon an energy increase in high-energy electrons precipitating into the atmosphere.

Modeling of extreme ultraviolet emissions from nonthermal gas discharges in air: the b(1) − X(0) band of molecular nitrogen

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.

Characterization of a transient spark micro-discharge in nitrogen using simultaneous two-wavelength diagnostics

A transient spark micro-discharge in nitrogen is investigated between two sharpened electrodes at a pressure of 0.5 bar. The plasma parameters (gas temperature, electron density and reduced electric field) are determined using optical emission spectroscopy (OES) and numerical simulations. The gas temperature of 3500 ± 100 K is determined by the comparison of the measured and simulated rotational distributions of the photoemission spectra of neutral molecular nitrogen N2(C-B,0–0). Both direct and stepwise electron impact excitation are considered in the collision-radiative model. The rate constants for electron impact excitation processes are calculated for different electric field values using the electron velocity distribution function, which is simulated by solving the Boltzmann equation. The applied broadband echelle spectrometer is absolutely calibrated in a spectral range of 200 nm to 800 nm, using two standard light sources, a deuterium lamp and a tungsten ribbon lamp, which are certificated by the Physikalisch-Technische Bundesanstalt (PTB), Germany. With the aid of this absolutely calibrated echelle spectrometer and a microwave atmospheric plasma source operated in a nitrogen flow, the intensified charge-coupled device (ICCD) camera, provided with an in-house made optical arrangement for simultaneous two-wavelength diagnostic is calibrated. The spatial resolution of this diagnostic system under the studied plasma conditions amounts to 13 µm. The accurate examination of the experimental results allows determining the dominant process of electron impact excitation of molecular nitrogen ion from ionic ground state. Applying the chosen excitation model of the nitrogen photoemission, the spatially resolved reduced electric field and the electron density are determined. This is done by using the inverse Abel transformation of the absolute intensities of molecular nitrogen bands N2(C-B,0–0) and (B-X,0–0), which were measured with the calibrated ICCD camera. The measured electric current of the micro-discharge is compared with the calculated one using the measured plasma parameters and a good coincidence is established.

Luminescence of Molecular Nitrogen Bands in the Earth’s Atmosphere during the Precipitation of High-Energy Electrons

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.

Luminescence of ND radicals during the destruction of molecular nitrogen nanoclusters

In this work we studied optical spectra of thermoluminescence accompanying the destruction of collections of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, and deuterium atoms. These collections of nanoclusters were formed by the injection of products of a radio-frequency discharge in deuterium-nitrogen-helium gas mixtures into bulk superfluid 4He. In the range from 200 to 1650 nm, the bands at 336 nm, 473 nm along with a new band at 1170 nm as well as the known bands of atomic nitrogen and oxygen, and bands of molecular nitrogen, oxygen, and NO were observed. These three bands were assigned to the emission of the ND radicals formed due to recombinations of nitrogen atoms in excited metastable states and deuterium atoms in the ground state during the destruction of ensembles of molecular nitrogen nanoclusters.

Characteristics of a novel nanosecond DBD microplasma reactor for flow applications

We present a novel microplasma flow reactor using a dielectric barrier discharge (DBD) driven by repetitive nanosecond high-voltage pulses. Our DBD-based geometry can generate a non-thermal plasma discharge at atmospheric pressure and below in a regular pattern of micro-channels. This reactor can work continuously up to about 100 min in air, depending on the pulse repetition rate and operating pressure. We here present the geometry and main characteristics of the reactor. Pulse energies of 1.46 and 1.3 μJ per channel at atmospheric pressure and 50 mbar, respectively, have been determined by time-resolved measurements of current and voltage. Time-resolved optical emission spectroscopy measurements have been performed to calculate the relative species concentrations and temperatures (vibrational and rotational) of the discharge. The effects of the operating pressure and flow velocity on the discharge intensity have been investigated. In addition, the effective reduced electric field strength has been obtained from the intensity ratio of vibronic emission bands of molecular nitrogen at different operating pressures and different locations. The derived increases gradually from about 550 to 4600 Td when decreasing the pressure from 1 bar to 100 mbar. Below 100 mbar, further pressure reduction results in a significant increase in up to about 10000 Td at 50 mbar.

The ratio of the intensities of 2P and 1P molecular nitrogen bands in apokamp discharge at different air pressures

The ratio of the intensities of 2P and 1P molecular nitrogen bands in apokamp discharge at different air pressures

Optical characteristics of the two-band barrier discharge excilamp on mercury monoiodide and mercury monobromide molecules

Introduction: An important direction in the development of excilamps is the study of working media emitting simultaneously several molecular bands of various exciplex molecules and or excimer molecules in the visible and ultraviolet spectral ranges in connection with possible applications in biotechnologies, medicine, and others. Purpose : The aim of the research was to determine the optical characteristics of a two-band excilamp on mercury monoiodide and monobromide molecules, the working media of which is a barrier discharge plasma on a mixture of mercury diiodide vapor and mercury dibromide vapor with helium and a small admixture of molecular nitrogen. . Methods: The development of a gas-discharge plasma and excitation of the components of the working mixture was carried out by a pulse-periodic barrier discharge with a pulse repetition rate of 1-20 kHz, pulse duration was 150 ns. Results : The ratio of the partial pressures of the components that give the maximum radiation yield at the wavelengths l max == 502 nm and l max = = 444 nm, namely: HgI 2 :HgBr 2 :N 2 :He = 0.1 kPa: 0.5 kPa: 2 kPa: 180 kPa are revealed. The following are achieved: the specific average and pulsed radiation power of 12 mW / cm 3 and 15.9 W / cm 3 , respectively, at a pulse repetition rate of 18 kHz, the efficiency of excilamp is ~ 15%. The long-term operation of the excilampi was detected (~ 10 7 pulses). Additional processes were found, that increase the population of the upper -state of mercury monohalides in the gas-discharge plasma, which are: additional processes of excitation of mercury monobromide molecules (-state)- the process of transfer of the population from the nitrogen molecule in metastable states of N 2 (), as well as the excitation of radicals by electrons in B 2 Σ + 1/2 -state of mercury monoiodide and mercury monobromide molecules. Conclusion : The optical characteristics of a two-band barrier discharge excilamp on a mixture of mercury diiodide and mercury dibromide with helium and a small addition of molecular nitrogen are established. The radiation spectrum consists of the predominant radiation of two spectral bands of mercury monoiodide and mercury monobromide exciplex molecules, and low-intensity spectral bands of molecular nitrogen, lines of helium atoms and mercury. It is established the regularities in the change of the dependence in optical characteristics of plasma on repetition rate of the pump pulses of the discharge and quantitative composition of mixtures. These studies are of interest for the production of exciplex gas-discharge sources (excilamps) that simultaneously radiate two bands in a visible spectral range.

Transition Energies and Absorption Oscillator Strengths for , , and Band Systems in N2

Abstract Theoretical transition energies and absorption oscillator strengths for the (v′ = 0–2, 5, 7, 8) − and (v′ = 0, 2) − (v″ = 0–14) Rydberg bands, and (v′ = 0–9, 11, 12, 14–19, 21, 22) − (v″ = 0–14) valence bands of molecular nitrogen are reported. The strong interaction between states has been dealt with through a vibronic interaction matrix. As a consequence of the Rydberg-valence interaction, irregularities in the vibrational structure of the above band systems are observed. Good agreement is found with the scarce high-resolution data that are available for oscillator strengths. The new band oscillator strengths reported here may be useful for a reliable interpretation of the spectra from atmospheres of the Earth, Titan, and Triton, where is the mayor constituent.

ABSORPTION OSCILLATOR STRENGTHS FOR THE (3, 4, 6)– (10, 13, 20)– AND (1)– PROGRESSIONS IN N2

ABSTRACT Absorption oscillator strengths, calculated with the molecular quantum defect orbital method, for the c 4 &prime; 1 &Sgr; u &plus; ?> (3)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12), c 4 &prime; 1 &Sgr; u &plus; ?> (4)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12), c 4 &prime; 1 &Sgr; u &plus; ?> (6)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12), b &prime; 1 &Sgr; u &plus; ?> (10)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12), b &prime; 1 &Sgr; u &plus; ?> (13)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12), b &prime; 1 &Sgr; u &plus; ?> (20)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12), and c 5 &prime; 1 &Sgr; u &plus; ?> (1)– X 1 &Sgr; g &plus; ( v &Prime; ?> = 0–12) bands of molecular nitrogen are reported. The Rydberg–valence interaction between states of 1 &Sgr; u &plus; ?> symmetry has been treated through an interaction matrix that includes vibrational coupling. Due to the homogeneous interaction, the intensity distribution of the bands within each progression deviates from the Franck–Condon predictions. The present results for vibronic transitions from the X 1 &Sgr; g &plus; ( 0 ) ?> ground state agree rather well with reported high-resolution measurements. As far as we know, f-values for bands originating from v″ &gt; 0 vibrational levels of the electronic ground state are reported here for the first time. These data may be useful in the interpretation of the extreme ultraviolet spectra from Earth’s and Titan’s atmospheres, in which several bands of the c 4 &prime; ( 3 ) , ?> c 4 &prime; ( 4 ) , ?> and c 4 &prime; ( 6 ) ?> progressions have been identified.

窒素分子発光スペクトル強度比を用いた大気圧ドライエアにおけるストリーマ放電の電界強度計測

窒素分子発光スペクトル強度比を用いた大気圧ドライエアにおけるストリーマ放電の電界強度計測

Spectral intensity of the N2 emission in argon low-pressure arc discharges for lighting purposes

Nitrogen is discussed as an alternative to hazardous mercury in lamps for general lighting. Molecular nitrogen bands emit in both the near-UV (the second positive system C3Πu → B3Πg) and the visible spectral range (the first positive system B3Πg → A3Σ+u), which reduces conversion losses. To analyse the potential of nitrogen, low-pressure arc discharges in an argon background were characterized by means of optical emission spectroscopy. The spectral intensity of the molecular nitrogen emission rises with increasing nitrogen content in the discharge and shows a maximum around 4 mbar of absolute pressure. With regard to the application as a light source, radiation efficiencies were determined, which are around 5% at maximum. In order to identify the main population processes a collisional radiative model for the nitrogen–argon system was established which reveals the high relevance of heavy-particle collisions due to a pressure of a few mbar. The decisive excitation reactions for the state N2 C3Πu are the well-known processes of energy pooling between metastable nitrogen molecules and energy transfer from metastable argon atoms. For the state N2 B3Πg the main population channels are collision-induced crossings within the nitrogen states, where the collision partner can be either a nitrogen molecule or an argon atom, and the quenching collisions with argon.

Atmospheric ultraviolet and red-infrared flashes from Universitetsky-Tatiana-2 satellite data

Millisecond ultraviolet (240–400 nm) and red-infrared (610–800 nm) flashes were detected in the nighttime atmosphere with the scientific payload installed onboard the Universitetsky-Tatiana-2 micro-satellite. Flashes with various numbers of photons, from 1020 to 1026, were detected within the atmospheric area 300 km in diameter observed by the detector. The flashes differ in duration and temporal profile: from single short flashes ∼1 ms in duration to flashes with a complex profile more than 100 ms in duration. Different global geographic distributions are observed for flashes with different numbers of photons. Flashes with fewer than 1022 photons are distributed uniformly over the Earth’s map. Flashes with more than 1022 photons are concentrated near the equator and above the continents. Series of flashes were observed in one turn of the satellite when flying not only over thunderstorm regions but also over cloudless ones. The flash number distribution has been derived from the ratio of the numbers of red-infrared and ultraviolet photons. As applied to discharges in the upper atmosphere, whose glow is dominated by the emission in the first and second positive systems of molecular nitrogen bands (1PN2 and 2PN2), this distribution is equivalent to the flash altitude distribution in the atmosphere. The observed ratio of the numbers of photons in red-infrared and ultraviolet flashes agrees with the calculated one for electric discharges at altitudes higher than 50 km. In-orbit measurements of the charged particle flux (with a threshold energy for electrons of 1 MeV) provide no evidence for a synchronous occurrence of an ultraviolet flash and a burst in the particle flux in the orbit.

Emission Dynamics of the Molecular Nitrogen Bands by Barrier Discharge in Air: Computer Modeling of the Experimental Procedure

Computer modeling is used to reproduce emission dynamics of (0-0) bands of the second positive and the first negative molecular nitrogen systems by a microdischarge channel in barrier discharge in atmospheric-pressure air. This gives a possibility to test the computational model and to evaluate the spectroscopic procedure of the electric field strength determination by the extended relative intensity technique. Computer modeling of the experimental procedure shows that averaging in space and time in experimental measurements may be the reason for the differences in the calculated and experimentally estimated values of E/N ; the last are considerably lower.

LINE ABSORPTION OSCILLATOR STRENGTHS FOR THE c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(0-5) BANDS IN N{sub 2}

Theoretical absorption oscillator strengths and emission branching ratios for rotational lines of the c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(0-5) bands of molecular nitrogen are reported. The calculations have been performed with the molecular quantum defect orbital method, which has proved to be reliable in previous studies of rovibronic transitions in diatomic molecules. The strong interaction between c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3) and b' {sup 1}{Sigma}{sup +}{sub u}(10) states has been analyzed through an interaction matrix that includes rotational terms. Owing to the perturbation, the c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(0), c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(1), and c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(5) bands are not weak, in contrast to what would be expected on the basis of the Franck-Condon principle. Moreover, the intensity distribution of the rotational lines within each of the vibronic bands deviates from considerations based on Hoenl-London factors. In this work, we provide data that may be useful to interpret spectra from atmospheres of the Earth, Titan, and Triton, in which transitions from the c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3) level have been detected.

LINE ABSORPTION OSCILLATOR STRENGTHS FOR THEc′41Σ+u(3)-X1Σ+g(0-5) BANDS IN N2

Theoretical absorption oscillator strengths and emission branching ratios for rotational lines of the c'4 1Σ+ u (3)-X 1Σ+ g (0-5) bands of molecular nitrogen are reported. The calculations have been performed with the molecular quantum defect orbital method, which has proved to be reliable in previous studies of rovibronic transitions in diatomic molecules. The strong interaction between c'4 1Σ+ u (3) and b' 1Σ+ u (10) states has been analyzed through an interaction matrix that includes rotational terms. Owing to the perturbation, the c'4 1Σ+ u (3)-X 1Σ+ g (0), c'4 1Σ+ u (3)-X 1Σ+ g (1), and c'4 1Σ+ u (3)-X 1Σ+ g (5) bands are not weak, in contrast to what would be expected on the basis of the Franck-Condon principle. Moreover, the intensity distribution of the rotational lines within each of the vibronic bands deviates from considerations based on Honl-London factors. In this work, we provide data that may be useful to interpret spectra from atmospheres of the Earth, Titan, and Triton, in which transitions from the c'4 1Σ+ u (3) level have been detected.

Time resolved optical emission spectroscopy of an HPPMS coating process

This paper deals with the time resolved optical emission spectroscopy of a high power pulse magnetron sputtering (HPPMS) physical vapour deposition coating process. With an industrial coating unit CC800/9 HPPMS (CemeCon AG, Würselen) a (Cr,Al,Si)N coating was deposited. During the coating process, an absolute calibrated Echelle spectrometer (ESA-3000) measured the intensities of the spectral lines of chromium (Cr), aluminium (Al) and molecular bands of nitrogen (N2). Time resolved measurements enable us to calculate different parameters such as the average velocity of sputtered Al and Cr atoms or the internal plasma parameters electron density ne and electron temperature kTe with a time resolution of 20 µs. With these parameters, we determine the ionization rates of Al, Cr, Ar and Kr atoms and the deposition densities of Al and Cr atoms. Thus simulated deposition densities of 1.75 × 1020 m−2 s−1 for chromium and 1.7 × 1022 m−2 s−1 for aluminium are reached.

High time-resolution sprite imaging: observations and implications

Sprites are large scale manifestations of electrical streamers triggered in the upper atmosphere by lightning in an underlying thunderstorm. Imaging of sprites at 10 000 frames per second has provided new insights into their spatial and temporal development. In this paper we discuss the experimental protocols that have been developed for performing high-speed observations of sprites and some new observations that have been obtained of relevance to laboratory experiments. Downward tendrils and upward branches, so characteristic in video recordings, are shown to be formed by very fast streamer heads with velocities up to half the speed of light. The streamer heads are spatially small, ∼100 m or less, but very bright with emission rates up to ∼1024 photons s−1. The sprite onset begins with a downward streamer. Then, in some sprites, at a little later time and from a lower altitude upward moving streamer heads may also appear. If there are no upward streamers the sprite would be classified as a ‘C-sprite’; with both downward and upward streamers it would be a ‘carrot sprite’. The optical emissions are primarily from the neutral molecular nitrogen first positive bands emitting in the near-infrared, but there are also blue emissions assumed to be from second positive bands of molecular nitrogen and from first negative bands of nitrogen ions. The streamer heads are observed at times to split into several streamer heads. This process appears to be more frequent in the core of larger sprites.