Electron‐impact dissociation of nitrogen

The highest oxidation state observed in graphene-supported sub-nanometer iron oxide clusters

Size-selected iron oxide nanoclusters are outstanding candidates for technological-oriented applications due to their high efficiency-to-cost ratio. However, despite many theoretical studies, experimental works on their oxidation mechanism are still limited to gas-phase clusters. Herein we investigate the oxidation of graphene-supported size-selected Fe_n clusters by means of high-resolution X-ray Photoelectron Spectroscopy. We show a dependency of the core electron Fe 2p_3/2 binding energy of metallic and oxidized clusters on the cluster size. Binding energies are also linked to chemical reactivity through the asymmetry parameter which is related to electron density of states at the Fermi energy. Upon oxidation, iron atoms in clusters reach the oxidation state Fe(II) and the absence of other oxidation states indicates a Fe-to-O ratio close to 1:1, in agreement with previous theoretical calculations and gas-phase experiments. Such knowledge can provide a basis for a better understanding of the behavior of iron oxide nanoclusters as supported catalysts.

Discussion on Electron Temperature of Gas-Discharge Plasma with Non-Maxwellian Electron Energy Distribution Function Based on Entropy and Statistical Physics

Electron temperature is reconsidered for weakly-ionized oxygen and nitrogen plasmas with its discharge pressure of a few hundred Pa, with its electron density of the order of 1017m-3 and in a state of non-equilibrium, based on thermodynamics and statistical physics. The relationship between entropy and electron mean energy is focused on based on the electron energy distribution function (EEDF) calculated with the integro-differential Boltzmann equation for a given reduced electric field E/N. When the Boltzmann equation is solved, chemical kinetic equations are also simultaneously solved to determine essential excited species for the oxygen plasma, while vibrationally excited populations are solved for the nitrogen plasma, since the EEDF should be self-consistently found with the densities of collision counterparts of electrons. Next, the electron mean energy U and entropy S are calculated with the self-consistent EEDF obtained, where the entropy is calculated with the Gibbs's formula. Then, the "statistical" electron temperature Test is calculated as Test=[∂S/∂U]-1. The difference between Test and the electron kinetic temperature Tekin is discussed, which is defined as [2/(3k)] times of the mean electron energy U=⟨ϵ⟩, as well as the temperature given as a slope of the EEDF for each value of E/N from the viewpoint of statistical physics as well as of elementary processes in the oxygen or nitrogen plasma.

Mechanisms for sonochemical oxidation of nitrogen

N₂O, and mixtures of N₂ and O₂, dissolved in water-both in the presence and absence of added noble gases-have been subjected to ultrasonication with quantification of nitrite and nitrate products. Significant increase in product formation upon adding noble gas for both reactant systems is observed, with the reactivity order Ne < Ar < Kr < Xe. These observations lend support to the idea that extraordinarily high electronic and vibrational temperatures arise under these conditions. This is based on recent observations of sonoluminescence in the presence of noble gases and is inconsistent with the classical picture of adiabatic bubble collapse upon acoustic cavitation. The reaction mechanisms of the first few reaction steps necessary for the critical formation of NO are discussed, illustrated by quantum chemical calculations. The role of intermediate N₂O in this series of elementary steps is also discussed to better understand the difference between the two reactant sources (N₂O and 2 : 1 N₂ : O₂; same stoichiometry).

Nitric oxide decomposition using atmospheric pressure dielectric barrier discharge reactor with different adsorbents

An NO removal rate of 99% and energy efficiency of 99.4 g NO per kW h were obtained on NaY zeolite using the adsorption–desorption and decomposition process in a self-made coaxial cylinder-type dielectric barrier discharge reactor.

Ion source for tests of ion behavior in the Karlsruhe tritium neutrino experiment beam line

An electron-impact ion source based on photoelectron emission was developed for ionization of gases at pressures below 10(-4) mbar in an axial magnetic field in the order of 5 T. The ion source applies only dc fields, which makes it suitable for use in the presence of equipment sensitive to radio-frequency (RF) fields. The ion source was successfully tested under varying conditions regarding pressure, magnetic field, and magnetic-field gradient, and the results were studied with the help of simulations. The processes in the ion source are well understood, and possibilities for further optimization of generated ion currents are clarified.

Combined crossed molecular beam and theoretical studies of the N(2D) + CH4 reaction and implications for atmospheric models of Titan

The dynamics of the H-displacement channel in the reaction N((2)D) + CH(4) has been investigated by the crossed molecular beam (CMB) technique with mass spectrometric detection and time-of-flight (TOF) analysis at five different collision energies (from 22.2 up to 65.1 kJ/mol). The CMB results have identified two distinct isomers as primary reaction products, methanimine and methylnitrene, the yield of which significantly varies with the total available energy. From the derived center-of-mass product angular and translational energy distributions the reaction micromechanisms, the product energy partitioning and the relative branching ratios of the competing reaction channels leading to the two isomers have been obtained. The interpretation of the scattering results is assisted by new ab initio electronic structure calculations of stationary points and product energetics for the CH(4)N ground state doublet potential energy surface. Differently from previous theoretical studies, both insertion and H-abstraction pathways have been found to be barrierless at all levels of theory employed in this work. A comparison between experimental results on the two isomer branching ratio and RRKM estimates, based on the new electronic structure calculations, confirms the highly nonstatistical nature of the N((2)D) + CH(4) reaction, with the production of the CH(3)N isomer dominated by dynamical effects. The implications for the chemical models of the atmosphere of Titan are discussed.

Removal of NO in NO/N2, NO/N2/O2, NO/CH4/N2, and NO/CH4/O2/N2 Systems by Flowing Microwave Discharges

In this paper, continuing previous work, we report on experiments carried out to investigate the removal of NO from simulated flue gas in nonthermal plasmas. The plasma-induced decomposition of small concentrations of NO in N2 used as the carrier gas and O2 and CH4 as minority components has been studied in a surface wave discharge induced with a surfatron launcher. The reaction products and efficiency have been monitored by mass spectrometry as a function of the composition of the mixture. NO is effectively decomposed into N2 and O2 even in the presence of O2, provided always that enough CH4 is also present in the mixture. Other majority products of the plasma reactions under these conditions are NH3, CO, and H2. In the absence of O2, decomposition of NO also occurs, although in that case HCN accompanies the other reaction products as a majority component. The plasma for the different reaction mixtures has been characterized by optical emission spectroscopy. Intermediate excited species of NO*, C*, CN*, NH*, and CH* have been monitored depending on the gas mixture. The type of species detected and their evolution with the gas composition are in agreement with the reaction products detected in each case. The observations by mass spectrometry and optical emission spectroscopy are in agreement with the kinetic reaction models available in literature for simple plasma reactions in simple reaction mixtures.

Low-Pressure DC Air Plasmas. Investigation of Neutral and Ion Chemistry

The neutral and charged species present in a direct current (dc) hollow cathode, gas flow, air reactor are experimentally studied by quadrupole mass spectrometry. The degree of ionization of the plasma and the electron mean temperature with decreasing air pressure, for constant discharge current, are measured with a double Langmuir probe. The chemical composition of the plasma changes appreciably over the 3 x 10(-3) to 5 x 10(-2) mbar range investigated: at the lowest pressures studied, O2 dissociation is up to 60% and the concentration of NO is half that of N2; concerning ions, NO+ and N2+ are dominant for the whole pressure range. A kinetic model of the plasma including electrons, neutrals, and positive ions is developed to account for the experimental observations; it is consistent with energy balance and predicts that heterogeneous processes are the main source of NO and that the contribution of ions to the global chemistry of neutrals is of minor significance even for the lowest pressures.

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn's giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan's early atmosphere, and that a wide range of initial atmospheric masses (all larger than the present value) can yield the measured enhancement. The enrichment in deuterated methane is now much better determined than it was when Pinto et al. (1986. Nature 319, 388-390) first proposed a photochemical mechanism to preferentially retain the deuterium. We develop a simple linear theory to provide a more reliable estimate of the relative dissociation rates of normal and deuterated methane. We utilize the improved data and models to compute initial methane reservoirs consistent with the observed enhancement. The result of this analysis agrees with an independent estimate for the initial methane abundance based solely on the present-day rate of photolysis and an assumption of steady state. This consistency in reservoir size is necessary but not sufficient to infer that methane photolysis has proceeded steadily over the age of the solar system to produce large quantities of less volatile organics. Our analysis indicates an epoch of early atmospheric escape of nitrogen, followed by a later addition of methane by outgassing from the interior. The results also suggest that Titan's volatile inventory came in part or largely from a circum-Saturnian disk of material more reducing than the surrounding solar nebula. Many of the ambiguities inherent in the present analysis can be resolved through Cassini-Huygens data and a program of laboratory studies on isotopic and molecular exchange processes. The value of, and interest in, the Cassini-Huygens data can be greatly enhanced if such a program were undertaken prior to the prime phase of the mission.