First Negative System Research Articles

Interplay between nitrogen oxides and ozone in a filamentary dielectric barrier discharge at various frequencies

AbstractPursuing more efficient nitrogen fixation in the context of the current climate crisis is of prime importance. The Haber‐Bosch process (NH3 production) accounts for at least 2% of the yearly released greenhouse gases. Alternatively, different atmospheric nonthermal discharges have proven their ability to convert nitrogen and oxygen from the air into nitrogen oxides (NO, NO2, and HNO3 hereafter referred as NOx). Among them, dielectric barrier discharges (DBDs) in N2/O2 are very interesting as they are characterized by microdischarges (MDs) developing into filaments under specific conditions (gap length, voltage, frequency, nature of the dielectrics). In this work, we used a sinusoidal voltage at 4, 12, 17.5, and 30 kHz as a key parameter to manipulate the MDs behaviors in an N2/O2 DBD and tailor the chemistry of the discharge. We characterized the MDs distribution by high‐speed camera imaging. Two different nitrogen emission systems, that is, the second positive system (SPS) and the first negative system (FNS), were used to assess the filament temperature and what we define as the delayed‐glow temperature, respectively. The influence of the filament's distribution on the overall discharge temperature has also been evaluated, by using a novel approach allowing the generation of heat distribution maps directly on a thermosensitive paper exposed to the discharge. Finally, the effect of the filaments on ozone (O3) and NOx production has been monitored by in situ Fourier‐transform infrared (FTIR). The DBD can be tuned between homogenously distributed MDs at 4 and 12 kHz to highly localized filaments at 17.5 and 30 kHz. A high filament temperature combined with a cold delayed‐glow is observed at 17.5 kHz while both the filament and the delayed‐glow temperature are high at 30 kHz. Low frequencies lead to heat spreading into the whole discharge volume, while localization of heat along the filament's paths is observed at high frequencies. High‐temperature filaments in the 30 kHz discharge and in the globally heated discharge at low frequencies quickly remove O3 from the discharge and consequently limit the overall NOx production by removing important oxidation pathways. On the contrary, filaments surrounded by cold gas observed at 17.5 kHz allowed to maintain a high concentration of O3 necessary for a faster oxidation of NO and thus increase the HNO3 production, even after 250 s, by avoiding backward reactions.

Effects of air relative humidity on spectral characteristics of dielectric barrier discharge plasma assisted combustion reactor

Using dielectric barrier discharge (DBD), a cylinder plasma assisted combustion (PAC) reactor was designed and applied to real aero-engines. Through the acquired optical emission spectroscopy (OES), the effects of air relative humidity (RH) on important active products (e.g. excited nitrogen molecules and hydroxyl radical) of this reactor discharges were investigated. In addition, vibrational temperature of N2* was calculated by Boltzmann plots. The OES of OH radials at 309 nm was analyzed. The results indicated that most OES of second positive system (SPS) N2*(CΠ3u→BΠ3g) had lower intensity at higher RH. The OES of first negative system (FNS) N2+ (391.4 nm) enhanced at 25 ~ 50% RH and reduced at 50~95%. Vibrational temperature of N2* reduced with the increased RH. When RH was lower than 35%, the OES of OH(A∑2→XΠ2) decreased with the increase of RH. While RH was higher than 35%, OH intensity increased. These research results could provide a vital basis for further studying the effects of DBD PAC reactor on combustion performances of aero-engines.

Electric field determination from intensity ratio of and N2 bands: nonequilibrium transient discharges in pure nitrogen

We developed an extension of the spectrometric method to estimate a reduced electric field (E/N), which is applicable in nitrogen-containing plasmas. The method is based on the intensity ratio of the emission bands of the first negative system (FNS) of and the second positive system (SPS) of N2. It uses the emission occurring in the wavelength interval 375–410 nm, which includes six SPS and two FNS bands. The choice of the spectral window is guided by much simpler acquisition and processing of experimental data than the SPS(0, 0) and FNS(0, 0) pair that is typically used. Following this idea, we construct a kinetic model for pure molecular nitrogen, which determines the population of the upper states responsible for the FNS and SPS emission. Moreover, we perform sensitivity analysis of the kinetic model, which allows us to reveal the most significant processes for the investigated intensity ratios. For these processes, we provide an in-depth review of the kinetic data that are available in the literature. We use the fact that the spectral window investigated contains bands to obtain three independent intensity ratios with sufficient signal-to-noise ratio ((FNS(0, 0)/SPS(0, 2), FNS(0, 0)/SPS(1, 4), FNS(0, 0)/SPS(2, 5)), which are usable for more accurate electric field determination. We also provide analytical formulas representing intensity ratio dependencies on E/N. Furthermore, we focus on different spectrometric representations of FNS and SPS bands, which also affect the precision of E/N determination. We examine the FNS/SPS band profiles in terms of different rotational temperatures and instrumental functions. Finally, we propose a simple procedure that enables the use of bandhead intensities in the intensity ratio dependencies, thus avoiding the need to evaluate integral band intensities from the recorded spectra.

Spectroscopic Diagnostic of Halos and Elves Detected From Space‐Based Photometers

AbstractIn this work, we develop two spectroscopic diagnostic methods to derive the peak reduced electric field in transient luminous events (TLEs) from their optical signals. These methods could be used to analyze the optical signature of TLEs reported by spacecraft such as Atmosphere‐Space Interactions Monitor (European Space Agency) and the future Tool for the Analysis of RAdiations from lightNIngs and Sprites (Centre National d'Études Spatiales). As a first validation of these methods, we apply them to the predicted (synthetic) optical signatures of halos and elves, two types of TLEs, obtained from electrodynamical models. This procedure allows us to compare the inferred value of the peak reduced electric field with the value computed by halo and elve models. Afterward, we apply both methods to the analysis of optical signatures of elves and halos reported by Global LIghtning and sprite MeasurementS (Japan Aerospace Exploration Agency) and Imager of Sprites and Upper Atmospheric Lightning (National Space Organization) spacecraft, respectively. We conclude that the best emission ratios to estimate the maximum reduced electric field in halos and elves are the ratio of the second positive system of N2 to first negative system (FNS) of N , the first positive system of N2 to FNS of N and the Lyman‐Birge‐Hopfield band of N2 to FNS of N . In the case of reduced electric fields below 150 Td, we found that the ratio of the second positive system of N2 to first positive system of N2 can also be used to reasonably estimate the value of the field. Finally, we show that the reported optical signals from elves can be treated following an inversion method in order to estimate some of the characteristics of the parent lightning.

OES characterization of streamers in a nanosecond pulsed SDBD using N2 and Ar transitions

The characterization of non-thermal homogeneous plasmas is possible using optical emission spectroscopy (OES), notably by estimating the reduced electric field. This method was applied to characterize streamers generated by a nanosecond pulsed surface dielectric barrier discharge (SDBD) operated in quiescent air at atmospheric pressure and also at 0.5 atm. The average reduced electric field associated with the surface streamers was determined using four different sets of transitions occurring in air plasmas, the first negative system (FNS) of , the first positive system (FPS) and second positive system (SPS) of and argon transitions . The analysis of the results allowed to critically assess the validity of the estimated reduced electric field for the present conditions. It is shown experimentally that the inhomogeneous nature of the streamer head influences significantly the estimation of the reduced electric field. Moreover, the estimated reduced electric field is not sufficient to characterize the processes taking place in the streamer head, due to the steep variation of both the reduced electric field E/N and the electron density ne in space and time. To overcome this limitation, a new method is proposed to take into account the spatial structure of a streamer head. The applicability of the new method is demonstrated for these experimental conditions and shows a very good agreement for the transitions tested.

Abnormal Enhancement of N2+ Emission Induced by Lower Frequency in N2 Dual-Frequency Capacitively Coupled Plasmas

Nitrogen dual-frequency capacitively coupled plasmas (DF-CCPs) with different frequency configurations, i.e., 60/2 MHz and 60/13.56 MHz, are investigated by means of optical emission spectroscopy (OES) and a floating double probe. The excited nitrogen molecule ion N2+(B) is monitored by measuring the emission intensity of the (0,0) bandhead of the first negative system (FNS) at 391.44 nm. It is shown that in the discharge with 60/13.56 MHz, the N2+ emission intensity decreases with the increase in pressure. In the discharge with 60/2 MHz, however, an abnormal enhancement of N2+ emission at higher pressure is observed when a higher power of 2 MHz is added. Variation in the ion density shows a similar dependence on the gas pressure. This indicates that in the discharge with 60/2 MHz there is a mode transition from the alpha to gamma type when a higher power of 2 MHz is added at high pressures. Combining the measurements using OES and double probe, the influence of low frequency on the discharge is investigated and the excitation route of the N2+(B) state in the discharge of 60/2 MHz is also discussed.

Thermometry in noble gas dielectric barrier discharges at atmospheric pressure using optical emission spectroscopy

We measure the temperature, T, of dielectric barrier discharges (DBD), in noble gases using optical emission spectroscopy (OES), by analysing rotational bands in the emission spectra of the first negative system (FNS) of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . This has the advantage that rotational structure can be fully resolved even with a spectrograph of average performance, and that the rotational temperature, T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> (~ T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gas</sub> ) can then be determined from a conventional Boltzmann plot. Ionization of N2 occurs mainly via Penning transfer from metastable excited states of He (ca. 20 eV) or Ne (ca. 16.6 eV). Using two glass-walled DBD chambers of very different volumes (0.1 and 20 liters), we have studied atmospheric-pressure discharges in flowing helium (He) or neon (Ne) containing traces of nitrogen. Discharges were excited by audio-frequency (10 kHz) high voltage (HV) using a needle as the HV electrode and a dielectric (alumina)-covered planar grounded counter-electrode. OE spectra were acquired with a 0.5 m focal length spectrograph, coupled to an intensified charge coupled device (ICCD) detector. Using the (0-0) R-branch of the FNS N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> (B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> - X <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) bands near a wavelength of 391.4 nm, we have measured axial (inter-electrode) distributions of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> for the two different reactor volumes in both He and Ne. T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> values were found to be highest at the needle electrode, of about 450 K and 740 K for He and Ne, respectively; in He, T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> dropped to a minimum of about 405 K at the mid-gap position in the small chamber, and ~ 360 K near the planar electrode in the large chamber. We conclude that temperatures in noble gas discharges depend critically on thermal conductivities of the particular gases (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">He</sub> = 1.9; K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ne</sub> = 0.6, both in mW.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> .K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and on other experimental factors that influence heat transfer.

Investigation of the transition between glow and streamer discharges in atmospheric air

Generally, the parameter p · d (pressure × gap distance) in dielectric barrier discharge (DBD) controls the electrical breakdown and also the plasma characteristics. We investigated the optimum plasma transition p · d by controlling the pressure. To find the transition p · d (p · dtr) condition, optical emission spectroscopy (OES) was used to measure emission spectra from the DBD. All p · d data were normalized by the second positive system of nitrogen molecules, the wavelength of which was 337.1 nm. Then we compared the relative intensities of species generated during the discharge by OES analysis. Species selected for comparison were the first negative system (FNS) of nitrogen molecules (391.4 nm) and atomic oxygen spectra (777.1 nm). Experimental results showed that relative intensities were almost constant as p · d decreased, but at specific p · d data, the intensity started to increase. The increase in FNS of nitrogen molecules means not only an increase in electron energy but also a change in the plasma mode, streamer to glow transition. In the case of DBD using alumina with 1 mm thickness applied ac power, the plasma transition occurred at the 1 Torr cm condition.

N2+first-negative emission cross sections for low-energyH+and H impact onN2

Absolute emission cross sections for the (0,1), (1,2), and (2,3) band emission sequence of the ${\mathrm{N}}_{2}^{+}$ first-negative system have been measured for low-energy ${\mathrm{H}}^{+}$ and H collisions with room-temperature ${\mathrm{N}}_{2}$ molecules. The energy range covered for ${\mathrm{H}}^{+}$ impact was from 63 eV to 2.0 keV, and that for H impact was from 160 eV to 2.5 keV. For H+${\mathrm{N}}_{2}$ collisions, cross sections for ${\mathrm{N}}_{2}$ second-positive emissions for the (1,5) and (2,6) emission bands were also determined. The total cross sections for production of ${\mathrm{N}}_{2}^{+}$($B$) and ${\mathrm{N}}_{2}$($C$) were determined from these measured results. The techniques used to accomplish the measurements are described, and the cross sections obtained are compared with the results of other investigations.

Catalysis and quenching of N2 afterglows by SF6

Spectra are presented from flowing afterglows in N2 produced by a microwave discharge. The luminescence from pure N2 discharges can be characterized as a typical Lewis-Rayleigh afterglow with no molecular emission in the ultraviolet. Trace amounts of SF6 added upstream of the discharge greatly enhance the first-positive emission from the afterglow and produce intense emission from the N+2 first-negative system and the appearance of N2 second-positive emission. Further SF6 addition downstream of the microwave discharge quenches the N+2 first-negative bands but causes no appreciable change in the emission from the N2 second-positive bands. Increasing the SF6 added prior to the discharge by a factor of 15 results in complete quenching of all N2 ultraviolet emission which is replaced by NS B-X luminescence.

Auroral emission of the N2+Meinel bands

New cross sections for electron impact excitation and quenching of the N2+ Meinel bands have been combined with recently determined transition probabilities to yield altitude profiles of the Meinel bands relative to those for the N2+ first-negative system. Quenching of the Meinel bands is found to compete with radiative decay for altitudes less than 120 km, and the quenching height (the altitude at which one half of the excited molecules are collisionally deactivated) is found to be approximately 85 km. The calculated intensity of the Meinel band system relative to that of the first-negative system agrees reasonably well with the more recent auroral measurements.

Spectroscopic diagnostics of R.F. discharges at moderate pressure and chemical applications—I. Pure nitrogen

A vibro-rotational analysis has been performed of the second positive system (SPS) of N 2 and of the first negative system (FNS) of N + 2 emitted by 35 MHz discharges in flowing nitrogen operated at pressures of 5–50 torr and power densities of the order of 1–10 W-cm -3. The distributions of the vibrational and of the rotational levels follow Boltzmann's law in both the SPS and the FNS with T v = 4000°K and T R = 2800°K for the N 2( C 3Π u ) state and T v = 5100°K and T R = 5800°K for the N + 2( B 2Σ + g ) state and independent of pressure. Kinetic gas temperatures are between 1200 and 2000°K and increase with pressure; electron temperatures are in the range 15,000–9,500°K. The reversal of line intensities of the SPS and of the FNS observed with increasing pressure has been tentatively interpreted. Possible chemical implications of these results have been examined.

Excitation ofN2+ions by collisions with rare-gas atoms

Collisions of 0.3-5-keV (4-20\ifmmode\times\else\texttimes\fi{}${10}^{6}$ cm/sec) ${\mathrm{N}}_{2}^{+}$ ions with He and Ne targets have been studied by spectroscopic observation of the ${\mathrm{N}}_{2}^{+}$ first-negative-emission spectrum. Vibrational excitation within the collisionally excited $X^{2}\ensuremath{\Sigma}_{g}^{+}\ensuremath{\rightarrow}B^{2}\ensuremath{\Sigma}_{u}^{+}$ transition in ${\mathrm{N}}_{2}^{+}$ was studied by a measurement of the relative band intensities of the $\ensuremath{\Delta}v=\ensuremath{-}1$ sequence of the first-negative system. Rotational excitation was examined by observation of the rotational line intensities of the (0,0) first-negative band ($\ensuremath{\lambda}=3914$ \AA{}A). Although the ${\mathrm{N}}_{2}^{+}$ ions used for these experiments were highly vibrationally and rotationally excited by the ion-source discharge, the initial-energy distribution could be inferred from the ${\mathrm{N}}_{2}^{+}$ emission spectra produced by high-velocity ($v&gt;1.2\ifmmode\times\else\texttimes\fi{}{10}^{7}$ cm/sec) collisions. At these velocities, populations of vibrational levels in the upper state were independent of projectile-ion velocity and the rotational-energy distribution corresponded to a Boltzmann distribution at 3700 \ifmmode^\circ\else\textdegree\fi{}K. At lower velocities, the population of high vibrational states increased with decreasing velocities and deviations from a Boltzmann distribution among rotational states were observed. Excitation to high rotational states increased monotonically with decreasing projectile-ion velocity. No differences in the rotational and vibrational excitation produced by He and Ne were observed. These results show that for some ion-molecule collisions there is vibrational and rotational excitation in the direct electronic excitation (non-charge-transfer) channel.

Der zeitliche Intensit�tsverlauf im nachleuchtenden Plasma reinen Stickstoffs

The afterglow of nitrogen especially prepared to produce an auroral afterglow was investigated after excitation with r. f. discharge. The intensity of the first-positive system, the second-positive system, and the first-negative system showed after a remarkable drop an increase to a maximum. The height and the timal occurrence of the maximum have been investigated quantitatively as function of pressure and excitation conditions. The maximum could only be observed with pressures >1,8 Torr. There is strong evidence that the afterglow emissions of the three band systems during the maximum is governed by a special excitation mechanism common to all band systems.

A New Method for Producing the Auroral Afterglow of Nitrogen and Its Spectrum

A new method for producing the auroral afterglow has been devised. No pre-operation of the afterglow tube is required and the afterglow is much stronger than that produced by Kaplan’s method.The spectrum of the auroral afterglow is analyzed. In the first-positive system, the vibrational levels of the upper state were extended to v = 26 and for the lower state to v = 20. In the second-positive system, new bands were observed which have been tentatively ascribed to a transition from v′ = 5. It was determined that the Goldstein-Kaplan bands belong to a single system, the 3Π − B3Πg. Three heads were measured for each band of the G-K system. The Vegard-Kaplan bands and the first-negative system were also observed and are reported on.The lifetime of the auroral afterglow and the excitation processes for the afterglow are discussed.

Measurement of Pressures in the Upper Atmosphere

IN the course of a series of photographs of the spectrum of the auroral afterglow in pure nitrogen at pressures varying from about 1 mm. to 0.01 mm., it was observed that the ratio of the intensity of the first-negative system of bands to that of the second-positive system changed gradually as the pressure changed. The first negative bands, which are emitted by the molecule ion, increased in intensity until, at the lowest pressure at which it was possible to photograph the afterglow, the spectrum consisted almost entirely of bands due to the ionized molecule.