N2 Vibrational Temperature Research Articles

Characterization on the temperature of radio frequency argon capacitive discharge mode transition at atmospheric pressure

The mode transition and coexistence were investigated in atmospheric pressure argon radio frequency capacitive discharge. By use of a program compiled by the authors for the nitrogen's second positive band simulation, comparison between the experimental and simulated spectra of band (0, 1) and (1, 2) was used to determine the rotational and vibrational temperatures of N2. The trends of vibrational and rotational temperatures with discharge power were studied to observe the temperature jump corresponding to the discharge mode transition. Utilizing a well-known software named Lifbase, the simulated spectra of OH (A—X)(0, 0) was calculated to obtain the rotational temperature of OH by comparing with the experimental OH (A—X)(0, 0) band. The calculated rotational temperature of OH is well consistent with the result of nitrogen's second positive band, which shows that the neutral species are at thermal equilibrium in the space of discharge. According to the current-voltage characteristic, the temperature jump corresponding to the discharge mode transition was confirmed in accordance with the photograph of discharge.

Influence of excitation voltage waveform on dielectric barrier discharge plasma aerodynamic actuation characteristics

Plasma flow control, based on the plasma aerodynamic actuati on generated by air discharge, is an active field in aerodynamics due to its potential application in performance improvement of future aircraft. In order to better understand the underlying physical mechanism of plasma flow control, it is i mportant to investigate the relationship between the operating parameters and the plasma aerodynamic actuation characteristics. This paper reports the electrical, optical and mech anical characteristics of surface dielectric barrier discharge p lasma aerodynamic actuation excited by microsecond and nanosecond high voltage waveforms. The nanosecond discharge is more diffuser than the microsecond discharge and the discharge current is much larger at the same applied voltage amplitude. The optical emission intensity of the nanosecond discharge plasma is stronger than that of the microsecond discharge plasma, while the rotational and vibrational temperatures of N2 in the nanosecond discharge plasma are less. In addition, the relative intensity of the first negative system of N + 2 (B 2 � + u ! X 2 � + g ) and the second positive system of N2(C 3 �u ! B 3 �g) is much less in the nanosecond discharge plasma. The velocity measurements indicate that the air flow induced by the nanose cond discharge plasma aerodynamic actuation is vertical to the dielectric surface, while that induced by the microsecond discharge actuation is parallel to the dielectric surface.

Growth, structure, and mechanical properties of hydrogenated amorphous carbon nitride films deposited by CH3CN dielectric barrier discharges

Hydrogenated amorphous carbon nitride (a-C:N:H) films were synthesized with CH3CN dielectric barrier discharges (DBD) plasmas. The effects of varying the CH3CN pressure (p) and the frequency of the power supply (f) on the film growth and film properties were studied. The deposited films were characterized using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy (AFM), and AFM-based nanoindentation. p and f were found to significantly influence the structures, compositions, deposition rates, surface roughness, and nanohardess of deposited a-C:N:H films. The experimental results indicate that dense a-C:N:H films with extremely low surface roughness (rms<1.0 nm) can be deposited with CH3CN DBD plasmas at f=1 kHz and p=∼100 Pa. The deposition systems were in situ characterized by means of optical emission spectroscopy. The emission intensities of major radicals, such as CN (B Σ2→X Σ2) and NH (A Π3→X Σ3) significantly increased with increasing f or decreasing p. N2 molecules were formed in the residual gas as a stable product, which leads to a decrease in the N/C ratio in deposited a-C:N:H films. The rotational and vibrational temperature of N2 C Π3 states in CH3CN and N2 DBD plasmas were examined and the N2 molecules produced in CH3CN DBD plasmas had the rotational temperature of ∼2000 K and vibrational temperature of ∼500 K. In the N2 DBD plasma, the rotational and vibrational temperature of the N2 molecules were 470±10 and 2850±50 K, respectively. The basic chemical reactions in the gas phase are presented and correlations between the film properties, the gas-phase plasma diagnostic data, and the film growth processes are discussed.

Plume dynamics of laser produced air plasma

Dynamical evolution of air spark (plume) created using ns and ps laser pulses is investigated. Two dimensional temporal evolution images of the spark are recorded using intensified CCD orthogonal to the laser propagation direction. Optical emission spectroscopy is used to determine temperature and density of plasma. Assuming local thermodynamic equilibrium of plasma electron temperature ~ 1.1 eV and an electron density ~ 1. 73 × 1018 cm-3at the 210 mJ energy and vibrational temperature of N2+ ~ 0.45 eV is determined. The dependence of the electron density on the laser energy and delay time after the initiation of the spark is discussed. To study the plasma channel by hydrodynamic evolution of air spark in the laser focus, an experiment using pump probe configuration is done. An increase in the length by a factor of ~3 and increase in electron density by a factor of 1.5 was observed at 7 ns delay of the nanosecond pulse relative to the picoseconds laser pulse. An extensive investigation of channel formation will be discussed.

The influence of Exciting Frequency on N2 and N2+ Vibrational Temperature of Nitrogen Capacitively Coupled Plasma

By using optical emission spectroscopy (OES), N2 and N2+ vibrational temperatures in capacitively coupled plasma discharges with different exciting frequencies are investigated. The vibrational temperatures are acquired by comparing the measured and calculated spectra of selected transitions with a least-square procedure. It is found that N2 and N2+ vibrational temperatures almost increase linearly with increasing exciting frequency up to 23 MHz, then increase slowly or even decrease. The pressure corresponding to the maximum point of N2 vibrational temperature decreases with the increasing exciting frequency. These experimental phenomena are attributed to the increasing electron density, whereas the electron temperature decreases with exciting frequency rising.

Spectroscopic study on rotational and vibrational temperature of N2 and N2+ in dual-frequency capacitively coupled plasma

By using optical emission spectroscopy, the vibrational and rotational temperatures of N2 and N2+ in capacitively coupled plasma (CCP) discharges driven by dual-frequency 41MHz and 2MHz are investigated. The vibrational and rotational temperatures are measured based on the N2+ first negative system and N2 second positive system overlapped molecular emission optical spectrum, using the method of comparing the measured and calculated spectra with a least-square procedure. The influence of the rotational and vibrational temperatures with input power of the high frequency (HF) and low frequency (LF) as well as the gas pressure is discussed. It is found that the vibrational or rotational temperatures of N2 and N2+ are decoupled in dual-frequency CCP discharge. The influence of the LF power on N2+ rotational and vibrational temperature is much more than that of N2, while the influence of HF power is just opposite to the case of LF power. The reason for this is thought to be the variation of electron temperature when applying HF or LF power. Additionally, the increase of gas pressure makes the difference between the vibrational and rotational temperature decrease.

Gas temperature measurements in a microwave plasma by optical emission spectroscopy under single-wall carbon nanotube growth conditions

Plasma gas temperatures were measured via in situ optical emission spectroscopy in a microwave CH4–H2 plasma under carbon nanotube (CNT) growth conditions. Gas temperature is an important parameter in controlling and optimizing CNT growth. The temperature has a significant impact on chemical kinetic rates, species concentrations and CNT growth rates on the substrate. H2 rotational temperatures were determined from the Q-branch spectrum of the (0) transition. N2 rotational and vibrational temperatures were measured by fitting rovibrational bands from the N2 emission spectrum of the C 3Πu → B 3Πg transition. The N2 rotational temperature, which is assumed to be approximately equal to the translational gas temperature, increases with an increase in input microwave plasma power and substrate temperature. The measured H2 rotational temperatures were not in agreement with the measured N2 rotational temperatures under the CNT growth conditions in this study. The measured N2 rotational temperatures compared with the H2 rotational temperatures suggest the partial equilibration of upper excited state due to higher, 10 Torr, operating pressure. Methane addition in the hydrogen plasma increases the gas temperature slightly for methane concentrations higher than 10% in the feed gas.

Experimental Research of OH and N 2 + Spatially Resolved Spectra in a Needle-Plate Pulsed Streamer Discharge

In this study, the spatial distributions of the emission intensity of OH ( $$\hbox{A}^{2}\Upsigma {\rightarrow}\hbox{X}^{2}\Uppi,$$ 0-0) and $$\hbox{N}_{2}^{+} (\hbox{B}^{2}\Upsigma_{\rm u}^{+}\rightarrow \hbox{X}^{2}\Upsigma_{\rm g}^{+},$$ 0-0, 391.4 nm) are investigated in the atmospheric pressure pulsed streamer discharge of H2O and N2 mixture in a needle-plate reactor configuration. The effects of pulsed peak voltage, pulsed repetition rate, input power, and O2 flow rate on the spatial distributions of the emission intensity of OH ( $$\hbox{A}^{2}\Upsigma {\rightarrow}\hbox{X}^{2}\Uppi,$$ 0-0), $$\hbox{N}_{2}^{+} (\hbox{B}^{2}\Upsigma _{\rm u}^{+} \rightarrow \hbox{X}^{2}\Upsigma _{\rm g}^{+},$$ 0-0, 391.4 nm), and the vibrational temperature of N2 (C) in the lengthwise direction from needle to plate are attained. It is found that the emission intensities of OH ( $$\hbox{A}^{2}\Upsigma {\rightarrow}\hbox{X}^{2}\Uppi,$$ 0-0) and $$\hbox{N}_{2}^{+} (\hbox{B}^{2}\Upsigma_{\rm u}^{+} \rightarrow \hbox{X}^{2}\Upsigma_{\rm g}^{+},$$ 0-0, 391.4 nm) rise with increasing the pulsed peak voltage, the pulsed repetition rate and the input power, and decrease with increasing O2 flow rate. In the direction from needle to plate, the emission intensity of OH ( $$\hbox{A}^{2}\Upsigma {\rightarrow}\hbox{X}^{2}\Uppi,$$ 0-0) decreases firstly, and rises near the plate electrode, while the emission intensity of $$\hbox{N}_{2}^{+}(\hbox{B}^{2}\Upsigma_{\rm u}^{+} \rightarrow \hbox{X}^{2}\Upsigma_{\rm g}^{+},$$ 0-0, 391.4 nm) is nearly constant along the needle to plate direction firstly, and rises sharply near the plate electrode. The vibrational temperature of N2 (C) is almost independent of the pulsed peak voltage and the pulsed repetition rate, but rises with increasing the O2 flow rate and keeps nearly constant in the lengthwise direction. The main physicochemical processes involved are discussed.

Optical study of OH radical in a needle-plate DC corona discharge

In this study, the emission spectra of OH (A2Σ → X2Π, 0-0) and N2 (C3Πu → B3Πg) emitted from the high-voltage DC (direct-current) corona discharge of N2 and H2O mixture gas in a needle-plate reactor are successfully recorded at one atmosphere. The relative vibrational populations and the vibrational temperature of N2 (C, v') in negative DC corona discharge are determined. The effects of discharge voltage, input power and added oxygen on the relative populations of OH (A2Σ) radicals and N2 (C3Πu) molecules in negative DC corona discharge are investigated. It is found that the relative populations of OH (A2Σ) radicals and N2 (C3Πu) molecules increase with increasing the discharge voltage and the input power and decrease with increasing the added oxygen. The emission spectra produced by positive DC corona discharge are also studied for comparing with negative DC corona discharge. However, the emission spectrum of OH (A2Σ → X2Π, 0-0) is not obtained in positive DC corona discharge, only the emission spectrum of N2 (C3Πu → B3Πg) is observed. The effects of discharge voltage and input power on the relative populations of N2 (C3Πu) molecules in positive DC corona discharge are also investigated. The relative populations of N2 (C3Πu) molecules increase with increasing the discharge voltage and the input power. The main involved physicochemical processes have been discussed.

Measurements of N(4S) absolute density in a 2.45 GHz surface wave discharge by optical emission spectroscopy

We have generated a N2 flowing discharge sustained by surface waves employing a 2.45 GHz high frequency source. The N2 dissociation was studied in the discharge and post-discharge regions by optical emission spectroscopy (OES) as a function of the experimental parameters: discharge power (30–160 W) and absolute pressure (1–20 Torr), at 0.5 Slm−1 flow rate. The N(2p3 4S0) absolute density was measured in the discharge by actinometry. We have introduced the effect of the N2(X1 Σg+) vibrational temperature in the actinometry equation. Such a consideration was made based on the work of Catherinot and Sy (1979 Phys. Rev. A 20 1511) which presents a profound discussion about the quenching mechanism of the N(3p 4S0) by N2(X1 Σg+, v) states. The 811.5 nm Ar and 821.6 nm N lines, from 2p9 → 1s5 and 3p 4P0 → 3s 4P transitions have been utilized here. Both are easily observed in the surface wave discharge. Further, the NO chemical titration was carried out in the late post-discharge furnishing the N(2p3 4S0) absolute density in that region. The extinction point of the 580.4 nm band of the N2 1st positive system was measured. The density values obtained by actinometry are validated by comparison with those measured in the post-discharge region. The two sets of data, function of pressure and discharge power, may be related by the mass conservation equation. The work provides the experimental N(2p3 4S0) absolute density values as a function of power and pressure only by application of OES techniques. Moreover, we demonstrate here that the N(3p 4P0) state is quenched by N2(X1 Σg+, v ⩾ 2) molecules forming N2(b 1Πu, v = 0) and N(4S) states, in agreement with Catherinot and Sy.

Optical Study of Radicals (OH, O, H, N) in a Needle-plate Negative Pulsed Streamer Corona Discharge

Optical emission spectroscopy has been applied to study the OH radicals and O, H, and N active atoms produced by a high-voltage negative pulsed streamer corona discharge of N2 and H2O mixture gas in a needle-plate reactor at one atmosphere. The relative vibrational populations and the vibrational temperature of N2(C, v′) were determined. The effects of pulsed peak voltage, pulsed repetition rate, and the addition of O2 on the relative populations of OH(A2Σ) radicals, O(3p5P), Hα (3P), and N(3p4P) active atoms were investigated. It was found that the relative populations of those radicals increase with increasing pulsed peak voltage and pulsed repetition rate. The relative population of OH(A2Σ) radicals decreases with increasing O2 flow rate, while the relative populations of O (3p5P), Hα (3P), and N (3p4P) active atoms exhibit a maximum over the studied range of the O2 flow rate. The involved physicochemical processes have also been discussed.

Optical study of radicals (OH, O, H, N) in a needle-plate bi-directional pulsed corona discharge

In this study, analysis of optical emission spectra are used for the detection of OH (A2Σ) radicals and O (3p5P), Hα (3P) and N (3p4P) active atoms produced by the high-voltage bi-directional pulsed corona discharge of N2 and H2O mixture gas in a needle-plate reactor at one atmosphere. The relative vibrational populations and the vibrational temperature of N2 (C, v') are determined. The effects of pulse peak voltage, pulse repetition rate and the added O2 flow rate on the relative populations of OH (A2Σ) radicals and O (3p5P), Hα (3P) and N (3p4P) active atoms are investigated. It is found that when pulse peak voltage and pulse repetition rate are increased, the relative populations of those excited states radicals rise correspondingly. The relative population of OH (A2Σ) radicals decreases with increasing the flow rate of oxygen. The relative populations of O (3p5P), Hα (3P) and N (3p4P) active atoms increase with the flow rate of oxygen at first and exhibit a maximum value at about 30 ml/min. When the flow rate of oxygen is increased further, the relative populations of those excited states active atoms decrease correspondingly. The main involved physicochemical processes also have been discussed.

Numerical and experimental studies of an arc-heated nonequilibrium nozzle flow

The arc-heated high-temperature gas is rotationally and vibrationally excited, and partially dissociated and ionized. When such gas flows inside a nozzle, energy transfers from rotational and vibrational energy modes to translational energy mode, and, in addition, recombination reactions occur. These processes are in thermal and chemical nonequilibrium. The present computations treat arc-heated nonequilibrium nozzle flows using a six temperature model (translational, rotational, N2 vibrational, O2 vibrational, NO vibrational and electron temperatures), and nonequilibrium chemical reactions of air. From the calculated flow properties, emission spectra at the nozzle exit were re-constructed by using the code for computing spectra of high temperature air. On the other hand, measurements of N2+ (1−) emission spectra were conducted at the nozzle exit in the 20 kW arc-heated wind tunnel. Vibrational and rotational temperatures of N2 were determined using a curve fitting method on N2+ (1−) emission spectra, with the vibrational and rotational temperatures for N2 and N2+ being assumed equal. Comparison of the measured and computed results elucidated that the experimental temperatures were larger than the computed ones. At present, we are trying to reveal the main reason for the discrepancy between the computed and measured N2 vibrational and rotational temperatures.

Optical and electrical diagnostics of a non-equilibrium air plasma

An AC-driven, non-equilibrium, atmospheric pressure air plasma is generated within the gap separating a disc-shaped metal electrode and a water electrode. The typical OH emission intensity distribution is recorded by high-speed CCD camera. The temporal emission behaviour of OH(A–X) shows that the OH emission intensity stays relatively constant during most of the current cycle but decreases abruptly when the current is close to zero. The N2 rotational and vibrational temperatures are obtained by comparison of the simulated spectra of C 3Π u–B 3Πg (Δv = −2) band transition of nitrogen with the experimental results. They are about 1800 K and 2600 K, respectively. The electron density in the plasma is measured utilizing the electrical conductivity. It is found to be 7 × 1012 cm−3 in the centre of the discharge during the peak current of Ipeak = 40 mA. The electron density follows a Gaussian radial distribution with a typical width of 0.35 mm.

Simulation of the Processes of Formation and Dissociation of Neutral Particles in Air Plasma: Kinetics of Neutral Components

The results are given of calculations of the concentration of basic neutral particles and of the energy balance in an air plasma in the positive column of a d.c. discharge at pressures of 30 to 300 Pa and currents of 20 to 110 mA. The calculations are based on a combined solution of the Boltzmann equation; equations of vibrational kinetics for the ground states of molecules of N2, O2, and NO; and of the equations of chemical kinetics for these molecules, their excited states, and dissociation products. The results are compared with the measured concentrations of O(3 P) atoms and NO molecules and with the effective vibrational temperatures of N2(X 1Σ+ g ). The measured values of gas temperatures and temperatures of the reactor wall are used to find the fractions of energy transforming to heat in the plasma volume, which are compared with the calculation results.

Studies on Gas Purification by a Pulsed Microwave Discharge at 2.46 GHz in Mixtures of N2/NO/O2 at Atmospheric Pressure

Pulsed microwave discharges operated at atmospheric pressure in gas mixtures containing N2, O2, and NO are investigated experimentally and theoretically for various gas mixture constituents and operating conditions with respect to the ability of exhaust gas purification. The rotational gas temperature and the vibrational temperature of N2 are derived from CARS measurements. The composition of the exhaust gas after treatment is monitored using FTIR spectroscopy. The processes of the chemical, electronic, and vibrational kinetics are described by a model that has been developed to calculate the species densities. The results obtained show that in N2/NO gas mixtures an overall reduction of NOx takes place. In the case of N2/O2/NO gas mixtures, no net reduction of NOx is achieved for a pulsed microwave power below 3600 W, a pulse length of 50 μs, and a typical repetition frequency of 2 kHz.

CARS Diagnostic and Modeling of a Dielectric Barrier Discharge

Dielectric barrier discharges (DBD) with planar- and knife-shaped electrodes are operated in N2O2NO mixtures under a pressure of 20 and 98 kPa. They are excited by means of consecutive unipolar or bipolar high-voltage pulse packages of 10 kV at a pulse repetition rate of 1 and 2 kHz. The rotational and vibrational excitation of N 2 molecules and the reduction of nitric oxide (NO) in the discharge have been investigated using coherent anti-Stokes Raman scattering (CARS) technique. Rotational (gas) temperatures near the room temperature and vibrational temperatures of about 800 K at atmospheric pressure and 1400 K at a pressure of 20 kPa are observed. Therefore, chemical reactions of NO with vibrationally excited N 2 are probably insignificant. One-dimensional kinetic models are developed that balance 35 chemical reactions between 10 species and deliver equations for the population density of excited vibrational levels of N 2 together with a solution of the Boltzmann equation for the electrons. A good agreement between measured vibrational temperatures of N 2 , the concentration of NO, and calculated data is achieved. Modeling of the plasma discharge verifies that a DBD operated with a N2NO mixture reduces the NO content, the simultaneous presence of O 2 , already 1%, is enough to prevent the NO reduction.

Emission spectroscopy detection of N2 active species in plasma nitriding process

The present paper is a review of recent works related to the optical emission spectroscopy applied to the determination of ground state densities of N atoms in Ar-N2 flowing post-discharges. The effect of small quantities of H2 in the Ar-N2 discharge on N atom densities within the post-discharge has been analysed. The authors demonstrate that optical emission of Na impurity may be applied to the determination of the vibrational temperature of N2(X,v) states at the temperatures usual for nitriding of metals in Ar-N2 post-discharge. From the diagnostic of Ar-N2 post-discharges, it is clearly specified that nitriding of iron base alloys in a flowing post-discharge reactor is originating in N atoms, especially when a few H2 molecules are admixed into the Ar-N2 discharge. Finally, correlation between the N-atom density and the thickness of the iron nitrided layers when H2 is introduced into the Ar-N2 discharge are given.

Measurement and analysis of nitric oxide radiation in an arcjet flow

On the bases of the centerline enthalpy value deduced from heat transfer measurements and the NOZNT code, it is possible to predict the freestream conditions in an arcjet wind tunnel flow. The translational-rotational and vibrational temperature of NO is nearly reproducible by NOZNT. Relative to the electron and electronic temperatures, the vibrational temperature of N2 and NO are significantly lower at enthalpies of less than 45 MJ/kg. The enthalpy deduced from spectroscopic measurements is in rough agreement with that deduced from heat transfer measurements.

Three-dimensional modelling of processes in the fast-axial-flow CO2 laser

The previously developed three temperature approximation for the analysis of the processes in the industrial fast-axial-flow CO2 laser is applied to the general three-dimensional (3D) modelling of the compressible flow in the laser cavity. The 3D geometrical representation and the compressible flow formulation allowed us to describe the realistic flow pattern and the distribution of the laser parameters. Our model predicts the development of the velocity profile along the laser from one which is near parabolic due to turbulent jet impingement, to one which is representative of a turbulent pipe flow. The translational temperature, T, the vibrational temperature of the symmetric stretch mode of CO2 T1, (almost equal to the vibrational temperature of the double degenerate bending mode of CO2, T2), the vibrational temperature of the asymmetric stretch mode of CO2, T3, and the vibrational temperature of N2, T4, are shown to increase along the laser axis except under the inlet openings, with T reaching about 360 K, T1 approximately=T2 reaching about 400 K, and T3 and T4 reaching about 3000 K. The values of T and flow velocities away from the inlet openings coincide within the accuracy of about 10% to those predicted by the 2D model. The average values of T3 and T4 (about 2500 K) seem to be in better agreement with experimental observations than those predicted by the 2D model. The predicted population inversion reaches its maximum value of about 5*1020 m-3 inside the recirculation zones between the inlet openings. We believe that our approach to the modelling of the processes in the CO2 laser may have a wide range of scientific and industrial applications far beyond the particular type of laser discussed in this paper.