Rotational Temperature Of N2 Research Articles

Characterization of a direct dc-excited discharge in water by optical emission spectroscopy

Dc-excited discharges generated in water at the tip of a tungsten wire which is located at the orifice of a quartz capillary are investigated by time-averaged optical emission spectroscopy.Two distinctive discharge modes are observed. For small conductivities of the liquid the discharge is a streamer-like discharge in the liquid itself (liquid mode). For conductivities above typically 45 µS cm−1 a large vapour bubble is formed and a streamer discharge in this vapour bubble is observed (bubble mode).Plasma temperatures and electron densities are investigated for both modes. The gas temperature is estimated from the rotational temperature of N2(C–B) and is 1600 ± 200 K for the bubble mode and 1900 ± 200 K for the liquid mode. The rotational temperature of OH(A–X) is up to 2 times larger and cannot be used as an estimate for the gas temperature. The rotational population distribution of OH(A), ν = 0 is also non-Boltzmann with a large overpopulation of high rotational states. This discrepancy in rotational temperatures is discussed in detail.Electron densities are obtained from the Stark broadening of the hydrogen Balmer beta line. The electron densities in the liquid mode are of the order of 1021 m−3. In the bubble mode electron densities are significantly smaller: (3–4) × 1020 m−3. These values are compared with the Stark broadening of the hydrogen alpha and gamma lines and with electron densities obtained from current density measurements. The chemical reactivities of the bubble and liquid modes are compared by means of the hydrogen peroxide production rate.

Nonlinear CARS measurement of nitrogen vibrational and rotational temperatures behind hypervelocity strong shock wave

The hypervelocity strong shock waves are generated, when the space vehicles reenter the atmosphere from space. Behind the shock wave radiative and non-equilibrium flow is generated in front of the surface of the space vehicle. Many studies have been reported to investigate the phenomena for the aerospace exploit and reentry. The research information and data on the high temperature flows have been available to the rational heatproof design of the space vehicles. Recent development of measurement techniques with laser systems and photo-electronics now enables us to investigate the hypervelocity phenomena with greatly advanced accuracy. In this research strong shock waves are generated in low-density gas to simulate the reentry range gas flow with a free-piston double-diaphragm shock tube, and CARS (Coherent Anti-stokes Raman Spectroscopy) measurement method is applied to the hypervelocity flows behind the shock waves, where spectral signals of high space/time resolution are acquired. The CARS system consists of YAG and dye lasers, a spectroscope, and a CCD camera system. We obtain the CARS signal spectrum data by this special time-resolving experiment, and the vibrational and rotational temperatures of N2 are determined by fitting between the experimental spectroscopic profile data and theoretically estimated spectroscopic data.

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.

Optical Emission Spectroscopy Investigation of a Surface Dielectric Barrier Discharge Plasma Aerodynamic Actuator

The optical emission spectroscopy of a surface dielectric barrier discharge plasma aerodynamic actuator is investigated with different electrode configurations, applied voltages and driving frequencies. The rotational temperature of N2(C3∏u) molecule is calculated according to its rotational emission band near 380.5nm. The average electron energy of the discharge is evaluated by emission intensity ratio of first negative system to second positive system of N2. The rotational temperature is sensitive to the inner space of an electrode pair. The average electron energy shows insensitivity to the applied voltage, the driving frequency and the electrode configuration.

CARS法による5Km/s以上の高速衝撃波背後の窒素分子の振動・回転温度測定

CARS法による5Km/s以上の高速衝撃波背後の窒素分子の振動・回転温度測定

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.

Flow-field properties under deposition of films from low-density jets

Statistical methods in the direct simulation Monte Carlo procedure and the electron-beam fluorescence technique were applied to investigate the distribution of density and temperature in a monatomic jet. Initial conditions of investigated flows corresponded to ones under deposition of films from low-density jets. In calculations, the variable hard-sphere model for molecular interaction potential and the diffuse reflection model with complete thermal accommodation were used. Distribution of density of Ar atoms in the jet and in the vicinity of the substrate were measured by the spontaneous radiation of Ar i 5912 Å (transition 4p[1/2]←4d[3/2]0,1←1′) and Ar ii 4610 Å (4s′2D←4p′2F0,5/2←7/2) induced by the electrons. The temperature was evaluated with the rotational temperature of N2, a small portion (5%) of which was added into Ar. The quantities of rotational temperature were found by measuring the intensity of the rotational lines of the first negative system N+2 band. The experimental data provide information about profiles of density along and across the center line of a jet over a range of 1×10−3≤Kn*≤4×10−2. On the whole, the computed profiles of density are in good agreement with the measurements. The calculated properties in the vicinity of the substrate allowed the performance of a detailed analysis of the gas-surface interaction process. A good comparison of the computed profile of the flux of molecules, incident on the substrate, and data on the film thickness of a-Si:H were obtained.

Diagnostics of a microwave CO2 laser discharge by means of narrow-band BOXCARS

A narrow-band BOXCARS system has been used for spatially resolved diagnostics of a microwave discharge in an axial-flow CO2 laser module. Axial and transverse distributions of the vibrational and rotational temperatures of N2 and CO as well as those of the CO2 dissociation degree have been determined. They have been used as a reference for a vibrational kinetic model for the laser medium. This allowed determination of an approximate electron density distribution along the discharge tube. A CCD camera has been used for visualizing the intensity distribution in the beam overlap region and checking its effect on the CARS saturation behaviour.

Narrow-band BoxCARS applied to CO2 laser discharges

CARS (Coherent Anti-Stokes Raman Scattering) has developed into a powerful tool for studying molecular systems. One of its possibilities is to derive vibrational and rotational temperatures as well as concentrations of molecules from measurements of the energy level population differences. A very good spatial resolution of CARS technique is one of its important advantages. This feature has been utilized for making spatially resolved measurements of the vibrational and rotational temperatures of N2 in a d.c.-excited transverse-flow CO2 laser discharge. Apart from that also spectra of CO2, CO and O2 in the discharge have been taken, which allowed us to evaluate the spatial distributions of those components in the discharge. Additionally first investigations of a microwave-excited CO2 laser module have been performed for comparison.

The Ar+–He interaction potential and distribution function effects on swarm measurements of Ar++N2 reaction-rate coefficients using helium buffer gas

A b initio potentials for the X 2Σ+1/2, A1 2Π3/2, and A2 2Π1/2 states of ArHe+ are tested as to their ability to describe swarm measurements of gaseous ion transport coefficients. Also tested are potentials based on spectroscopic measurements and model potentials chosen specifically so as to match the transport data. Ar+-ion velocity distributions in a drift tube containing a helium buffer are calculated from the potentials that best match the mobility data, by solution of the Boltzmann kinetic equation. The velocity distributions are used with estimated cross sections for the charge-transfer reaction Ar++N2 to calculate the effects upon the rate coefficients when the distribution differs from a Maxwell–Boltzmann form. The results indicate that the corrections are small at high buffer gas temperatures (293 K and above) and low to moderate electric-field strengths, but become larger at low temperature (82 K) and high fields. The smallness of the corrections confirms that previous rate coefficient measurements in a drift tube show a dependence of the Ar++N2 reaction upon the rotational temperature of N2.

Evidence for an influence of rotational energy on the rate constants for the reaction of Ar+(2P3/2) with N2

Rate constants for the charge transfer reaction of Ar+(2P3/2) with N2 were measured as a function of average center-of-mass kinetic energy (〈KEcm〉) at three temperatures. The rate constants increase rapidly with (〈KEcm〉) at all temperatures. The thermal activation energy is derived to be 0.07 eV, which is approximately the value of the endothermicity of the reaction when N+2 (v=1) is produced. The rate constants vary with temperature at a particular 〈KEcm〉, indicating either an effect due to differing energy distributions in the drift tube at different temperatures or that the reactivity depends on the rotational temperature of N2. Comparing the data at constant average total energy indicates that translational and rotational energy have a similar effect on the reactivity.

Emission spectroscopy study of N2-H2 glow discharge for metal surface nitriding

A N2-H2 glow discharge for metallic surface nitriding at low pressure (1-3 Torr) and low current density (1-6 mA cm-2) has been studied by emission spectroscopy. The N2, N2+, N, N+, H, NH and metal atom excited states have been detected. The rotational temperature of N2+(B2 Sigma u+) states in the negative glow near the cathode surface has been found to be in quasi-equilibrium with the cathode temperature. By using argon as a gas impurity (2%), it has been established that the N2(C3 Pi u) states are excited in the negative glow near the cathode fall by direct electron impact. The NH radicals appear to issue near the cathode surface as do metal atoms.