Electron Impact Dissociation Of N2 Research Articles

Non-Thermal Nitric Oxide Formation in the Earth’s Polar Atmosphere

Auroral events are the prominent manifestation of solar/stellar forcing on planetary atmospheres because they are closely related to the stellar energy deposition by and evolution of planetary atmospheres. A numerical kinetic Monte Carlo model was developed with the aim to calculate the steady-state energy distribution functions of suprathermal N(4S) atoms in the polar upper atmosphere formed due to the precipitation of high-energy auroral electrons in the N2-O2 atmospheres of rocky planets in solar and exosolar planetary systems. This model describes on the molecular level the collisions of suprathermal N(4S) atoms and atmospheric gas taking into account the stochastic nature of collisional scattering at high kinetic energies. It was found that the electron impact dissociation of N2 is an important source of suprathermal N atoms, significantly increasing the non-thermal production of nitric oxide in the auroral regions of the N2-O2 atmospheres of terrestrial-type planets.

Kinetic Study for Plasma Assisted Cracking of NH3: Approaches and Challenges.

Ammonia is considered as one of the promising hydrogen carriers toward a sustainable world. Plasma assisted decomposition of NH3 could provide cost- and energy-effective, low-temperature, on-demand (partial) cracking of NH3 into H2. Here, we presented a temperature-dependent plasma-chemical kinetic study to investigate the role of both electron-induced reactions and thermally induced reactions on the decomposition of NH3. We employed a plasma-chemical kinetic model (KAUSTKin), developed a plasma-chemical reaction mechanism for the numerical analysis, and introduced a temperature-controlled dielectric barrier discharge reactor for the experimental investigation using 1 mol % NH3 diluted in N2. As a result, we observed the plasma significantly lowered the cracking temperature and found that the plasma-chemical mechanism should be further improved to better predict the experiment. The commonly used rates for the key NH3 pyrolysis reaction (NH3 + M ↔ NH2 + H + M) significantly overpredicted the recombination rate at temperatures below 600 K. Furthermore, the other identified shortcomings in the available data are (i) thermal hydrazine chemistry, (ii) electron-scattering cross-section data of NxHy, (iii) electron-impact dissociation of N2, and (iv) dissociative quenching of excited states of N2. We believe that the present study will spark fundamental interest to address these shortcomings and contribute to technical advancements in plasma assisted NH3 cracking technology.

The Kinetic Monte Carlo Model of the Auroral Electron Precipitation into N2-O2 Planetary Atmospheres

Auroral events are the prominent manifestation of solar/stellar forcing on planetary atmospheres. They are closely related to the energy deposition by and evolution of planetary atmospheres, and their observations are widely used to analyze the composition, structure, and chemistry of the atmosphere under study, as well as energy fluxes of the precipitating particles that affect the atmosphere. A numerical kinetic Monte Carlo model had been developed, allowing us to study the processes of precipitation of high-energy auroral electrons into the N2-O2 atmospheres of the rocky planets in the Solar and exosolar planetary systems. This model describes on a molecular level the collisions of auroral electrons and atmospheric gas, taking into account the stochastic nature of collisional scattering at high kinetic energies. The current status of the kinetic model is illustrated in the applications to the auroral events on the Earth such as the production of suprathermal nitrogen atoms due to the electron impact dissociation of N2. It was found that electron impact dissociation of N2 can potentially be an important source of suprathermal N atoms in the auroral regions of the N2-O2 atmosphere of terrestrial-type planets. Such research will allow us to study the odd nitrogen chemistry as an atmospheric marker of the N2-O2 atmosphere of rocky exoplanets.

Kinetics of metastable N2(A3Σu + , v) molecules in high-pressure nonequilibrium plasmas

Absolute, time-resolved populations of N2(A3Σu +, v = 0–5) vibrational levels in high-pressure ns pulse discharge plasmas are measured by Tunable Diode Laser Absorption Spectroscopy (TDLAS). The diffuse plasma is generated by a repetitively pulsed, double dielectric barrier, ns discharge across a 10 mm gap in a plane-to-plane geometry, at pressures of up to 400 Torr. The results of TDLAS measurements in nitrogen and in H2–N2, O2–N2, and NO–N2 plasmas are compared with kinetic modeling predictions, identifying the mechanisms of N2(A3Σu +) generation and decay during the discharge pulses and in the afterglow. Comparison with the modeling predictions indicates that electron impact dissociation of N2 from the ground electronic state significantly underpredicts the yield of N atoms. The present data suggest that N2 dissociation in the plasma also occurs during the energy pooling process in collisions of two N2(A3Σu +) molecules. The results also show that high-pressure, high repetition rate, volume-scalable ns pulse discharges can be used for efficient generation of atomic species for plasma chemical and plasma catalysis syntheses. In an NO–N2 mixture, it is shown that the N2(A3Σu +) decay is controlled by the rapid energy transfer to NO, resulting in its electronic excitation and UV emission (NO γ bands). The diagnostics used in the present work can be used for the accurate characterization of both high-pressure, low-temperature gas discharge plasmas and high-temperature nonequilibrium flows generated in pulsed facilities such as shock tubes and expansion tunnels.

Selective generation of excited species in ns pulse/RF hybrid plasmas for plasma chemistry applications

Hybrid plasmas, sustained by a repetitive ns pulse discharge and a sub-breakdown RF waveform in N2 and its mixtures with H2, CO, and CO2, are studied using laser diagnostics and kinetic modeling. Plasma emission images show that adding the RF waveform to the ns pulse train does not result in a discharge instability development, since the RF field does not produce additional ionization. Unlike a ns pulse/DC discharge, the ns pulse/RF plasma is sustained using a single pair of electrodes external to the discharge cell. Measurements of electronically excited molecules, N2(A3Σu +), and vibrationally excited molecules in the ground electronic state, N2(X1Σg +, v), demonstrate that these species are generated selectively. N2(A3Σu +) molecules are produced predominantly by the ns pulse discharge waveform, while vibrational excitation of the ground electronic state N2 is mainly due to the RF waveform. Strong vibrational nonequilibrium is maintained at a low translational–rotational temperature. The ns pulse/RF discharge data demonstrate that the quenching of N2(A3Σu +) is not affected by N2 vibrational excitation. Kinetic modeling shows that the rate of N2(A3Σu +) quenching in a ns pulse discharge in nitrogen is underpredicted, and the modeling predictions agree with the data only if the rate of N atom generation by electron impact dissociation of N2 is increased by approximately an order of magnitude. This suggests a significant effect of excited electronic states on the net dissociation rate. Infrared emission spectra of ns pulse/RF hybrid plasmas in CO–N2 and CO2–N2 mixtures show that the present approach also generates strong vibrational excitation of CO and CO2, with the CO yield in the CO2–N2 mixture approximately a factor of two higher compared to that in a ns pulse discharge alone. This indicates a significant contribution of the vibrationally enhanced CO2 dissociation in the hybrid plasma. The present results demonstrate that sustaining the hybrid plasma in reacting molecular gas mixtures may isolate the plasma chemical reaction pathways dominated by vibrationally excited molecules from those of electronically excited molecules and atomic species.

Pulse Intense Electron Beam Irradiation on the Atmospheric Pressure N2 Containing 200 ppm of NO

Removal of nitrogen oxides (NOx) in N2 by the pulse intense electron beam irradiation was investigated. The pulse electron beam (kinetic energy; ≤160 keV, current; ∼140 A, current density; ∼2 A/cm2, pulse width; ∼700 ns and the electron beam energy in one pulse; 12.6±0.4 J) was injected into a gas cell filled with 1 atmospheric pressure N2 with an initial concentration of 200 ppm of NO. The NOx decreased quickly and only a small amount of NO2 was produced by the electron beam irradiation. Electron impact dissociation of N2 and the subsequent chemical reduction of NO by nitrogen radicals was occurred. The typical removal ratio in the gas cell of 1.7 l was about 20% for the first shot and reached to 95% after 8 successive shots. This removal ratio corresponds to the removal efficiency of 220–300 nmol/J. The NOx removal ratio and the efficiency which depended on the length of the gas cell, the filling pressure, the initial concentration of NO, the electron beam energy in one pulse and the axial magnetic field were investigated.

Nitric oxide abundance in the mesosphere/lower thermosphere region: Roles of solar soft X rays, suprathermal N(4S) atoms, and vertical transport

This paper carefully examines the inability of photochemical models to account for the large nitric oxide densities of ∼108 cm−3 at ∼105 km obtained from IR, UV, and microwave measurements. A detailed and up‐to‐date photochemical model is constructed that incorporates measured YOHKOH soft X ray fluxes, hot N atom chemistry with an energy dependent thermalization cross section and seven reaction sources, and laboratory‐constrained N(2D) yields. The resulting model which has well‐constrained chemistry compared to past models fails to generate high enough NO densities in comparison with the most reliable measurements of absolute NO concentrations in the lower thermosphere. The sensitivity of the model results and the known uncertainties in the inputs are used to identify where future efforts should be focused. A deficit remains despite an increase in the vertical mixing rates in the lower thermosphere from the very low Kzz profile used in our calculations and/or an increase in the N(2D) yield from electron impact dissociation of N2 from its nominal value of 0.54 to 0.62. The sensitivity of NO profiles to the nascent energy distributions of the atmospheric sources of suprathermal N atoms is illustrated by including the thermalization of suprathermal N atoms with an updated thermalization cross section. The diurnally averaged NO concentration at 105 km is enhanced by factors of 1.2 and 2.6 when the energy distributions of the N atoms from electron impact dissociation of N2 are chosen with peaks near 0.6 eV or 3–4 eV, but deficits of factors of ∼7 and ∼3, respectively, remain. There is higher sensitivity to vertical transport than to variations of chemistry within known uncertainties.

Atomic nitrogen in aurora: Production, chemistry, and optical emissions

The production of ground configuration nitrogen atoms in aurora is investigated. The two principal mechanisms are electron impact dissociation of N2 and chemical‐ionic reactions, with the latter dominating the production of N(²D). Between 60 and 70% of the N atoms are produced in the excited ²P and ²D states over a large altitude range. Simultaneous field‐aligned measurements of the 5200‐Å and 3466‐Å lines of N I and the 4278‐Å first negative group band of N2+ were made in the northern nightside auroral oval under varying auroral conditions. These data, taken over a continuous 4‐hour period on the night of February 5, 1978, yield an average emission rate ratio of the 5200‐Å/3466‐Å lines near 0.5. Model calculations yield ratios of 0.5 and 1.4 for particle characteristic energies (alpha) of 2 keV and 0.1 keV in an assumed Maxwellian electron spectrum in good agreement with the observations reported here and consistent with those reported in the literature for very soft precipitation in the dayside cusp region. The production rate of energetic (hot) N(4S) atoms in the aurora is evaluated from considerations of the excess translational energy associated with N atom production. It may be a significant factor in the production rate of NO and the odd nitrogen density in general in the auroral atmosphere.

EUV emission from Titan's upper atmosphere: Voyager 1 encounter

Analysis of Titan's EUV emission spectra obtained at the Voyager 1 encounter demonstrates that electron impact on N2 above 3600 km accounts for the bulk of the observed emission short of Lyman α. In conjunction with the UVS solar occultation data it is concluded that N2 is the major component of Titan's upper atmosphere, with upper limit mixing ratios at 3900 km on NeI, ArI, CO, H2, and HI of 0.01, 0.06, 0.05, 0.06, and 0.1, respectively. Magnetospheric electrons interact with Titan's sunlit hemisphere to produce a power dissipation rate of ≃2 × 109 W in the exosphere and ≃3 × 109 W below the exobase, with optical signatures from numerous N2 bands, NI, and NII multiplets. The N2 C4′ (0‐0) Rydberg band at 958 Å acts as an optical probe of Titan's exosphere because of transmission losses caused by fluorescence and predissociation. Magnetospheric electron precipitation produces an average dayside electron density of ≃3 × 10³ cm−3 between 3600 and 4000 km, the region of bright limb emission. When Titan is within Saturn's magnetosphere, magnetospheric electron impact dissociation of N2 generates an N atom escape rate of ≃3 × 1026 s−1 from Titan's exosphere. A nonthermal H atom escape rate of ≃2 × 1026 s−1 is estimated from magnetospheric electron impact ionization of N2 followed by reactions with CH4 and H2 and recombination to produce hot H atoms.

The relative intensity of the [N I] 1.04‐µ m multiplet as an indicator of the mean height of auroral forms

Quenching of N(²P) by atomic O has been included in the calculations used to estimate changes in mean emission heights of auroral forms previously studied by Vallance Jones and Gattinger (1978). Recent estimates of the production efficiency for N(²P) in electron impact dissociation of N2 permit a cross check on the estimated height from the intensity of the 1.04‐µ m [N I] multiplet. Satisfactory agreement is obtained if the atomic O concentration in the 110‐ to 120‐km region was about half that of the Jacchia (1971) model for a N(²P)‐O quenching rate coefficient of 10−11 cm³ s−1.