Plasma conductivity as a probe for ambient air admixture in an atmospheric pressure plasma jet

By utilizing a fully floating double electrical probe system, the conductivity of a linear atmospheric pressure plasma jet, utilizing nitrogen as process gas, was measured. The floating probe makes it possible to measure currents in the nanoamp range, in an environment where capacitive coupling of the probes to the powered electrodes is on the order of several kilovolts. Using a chemical kinetic model, the production of reactive nitrogen oxide and hydrogen-containing species through admixture of ambient humid air is determined and compared to the measured gas conductivity. The chemical kinetic model predicts an enhanced diffusion coefficient for admixture of O₂ and H₂O from ambient air of 2.7 cm² s^?1, compared to a literature value of 0.21 cm² s^?1, which is attributed to rapid mixing between the plasma jets and the surrounding air. The dominant charge carriers contributing to the conductivity, aside from electrons, are NO⁺, NO₂ ^? and NO₃ ^?. Upon admixture of O₂ and H₂O, the dominant neutral products formed in the N₂ plasma jet are O, NO and N₂O, while O₂(¹Δ_g) singlet oxygen is the only dominant excited species.     

Electron-transfer transitions during the collision of O2, N2, NO and CO with their respective ions

An improved theory of electron transfer absorption is proposed. The possibility of such absorption during the collision of ion-molecule pairs is discussed and frequencies for the O₂O₂⁺, O₂O₂^?, NONO^?, COCO⁺ and N₂N₂⁺ pairs are estimated. Oscillator strengths are also estimated for the O₂O₂⁺ pair.     

Chemical Effects of Air Plasma Species on Aqueous Solutes in Direct and Delayed Exposure Modes: Discharge,Post-discharge and Plasma Activated Water

The chemical interaction between non-thermal plasma species and aqueous solutions is considered in the case of discharges in humid air burning over aqueous solutions with emphasis on the oxidizing and acidic effects resulting from formed peroxynitrite ONOO^? and derived species, such as transient nitrite and stable HNO₃. The oxidizing properties are mainly attributed to the systems ONOO^?/ONOOH [E°(ONOOH/NO₂) = 2.05 V/SHE], ^·OH/H₂O [E°(^·OH/H₂O) = 2.38 V/SHE] and to the matching dimer system H₂O₂/H₂O [E°(H₂O₂/H₂O) = 1.68 V/SHE]. ONOOH tentatively splits into reactive species, e.g., nitronium NO⁺ and nitrosonium NO ₂ ⁺ cations. NO⁺ which also results from both ionization of ^·NO and the presence of HNO₂ in acidic medium, is involved in the amine diazotation/nitrosation degradation processes. NO ₂ ⁺ requires a sensibly higher energy than NO⁺ to form and is considered with the nitration and the degradation of aromatic molecules. Such chemical properties are especially important for organic waste degradation and bacterial inactivation. The kinetic aspect is also considered as an immediate consequence of exposing an aqueous container to the discharge. The relevant chemical effects in the liquid result from direct and delayed exposure conditions. The so called delayed conditions involve both post-discharge (after switching off the discharge) and plasma activated water. An electrochemical model is proposed with special interest devoted to the chemical mechanism of bacterial inactivation under direct or delayed plasma conditions.     

A flowing afterglow study of uranium tetraborohydride

Ionization-fragmentation of uranium(IV) tetraborohydride, U(BH₄)₄, by He⁺ and by N⁺/N₂⁺ yields, predominantly, U(BH₅)⁺ and U(B₂H₈)⁺, respectively. Attachment of thermal electrons yields U(BH₄)₄^? and ions of 1, 2, and 3 mass units less. Fluoride transfer with SF₆^?, BF₄^?, and UF_n^? (n = 5–7) and reactions with other small ions (O^?, O₂^?, NO₂^?, F^?, Cl^?, O₂⁺) are described.     

Sputtered ammonium dinitramide: Tandem mass spectrometry of a new ionic nitramine

The recently synthesized ammonium dinitramide (ADN) is an ionic compound containing the ammonium ion and a new oxide of nitrogen, the dinitramide anion (O₂N? N? NO₂^?). ADN has been investigated using high-energy xenon atoms to sputter ions directly from the surface of the neat crystalline solid. Tandem mass spectrometric techniques were used to study dissociation pathways and products of the sputtered ions. Among the sputtered ionic products were NH₄⁺, NO⁺, NO₂^?, N₂O₂^?, N₂O, N₃O₄^? and an unexpected high abundance of NO₃^?. Tandem mass spectra of the dinitramide anion reveal the uncommon situation where a product ion (NO₃^?) is formed in high relative abundance from metastable parent ions but is formed in very low relative abundance from collisionally activated parent ions. It is proposed that the nitrate anion is formed in the gas phase by a rate-determining isomerization of the dinitramide anion that proceeds through a four-centered transition state. The formation of the strong gas-phase acid, dinitraminic acid (HN₃O₄), the conjugate acid of the dinitramide anion, was observed to occur by dissociation of protonated ADN and by dissociation of ADN aggregate ions with the general formula [NH₄(N(NO₂)₂)_n] NH₄⁺, where n = 1–30.     

Nitrosonium nitrite isomer of N<Subscript>2</Subscript>O<Subscript>3</Subscript>: Quantum-chemical data

The geometrical, electronic, and thermodynamic parameters of three known isomers of dinitrogen trioxide N₂O₃ were calculated by the density functional theory DFT/B3LYP method using the 6-311++G(3df) basis. The structure of the new isomer, NONO₂, was calculated. From the calculation of vibrational frequencies it follows that the structure of NONO₂ has a local potential energy minimum and corresponds to the stationary state of the N₂O₃ isomer. The molecular structure of NONO₂ is characterized by a substantial negative charge on the NO₂ fragment and positive charge on the NO fragment. The electronic structure of the NO⁺NO ₂ ^? isomer can be characterized as nitrosonium nitrite, which can be oxidized to nitrite and participate in nitrosylation in accordance with the biogenic characteristics of the NO _x intermediate, assumed to be formed in biological systems during the oxidation of NO.     

Nitrogen Fixation as NOx Enabled by a Three-Level Coupled Rotating Electrodes Air Plasma at Atmospheric Pressure

In this paper, a three-level coupled rotating electrodes air plasma at atmospheric pressure is developed for evaluation of nitrogen fixation. Factors influencing the NO_x production rate and energy cost, including airflow rate, the input H₂O concentration, blade numbers at each rotating electrode and rotating speed, are examined. Air flow rates prove to have no effect on the rotational temperature of N₂ 337.1 nm and the emission intensities of N₂⁺ and N₂, but specific energy input (SEI) and species’ residence time can be shorter with higher air flow rates, resulting in lower NO_x concentration and energy cost. The addition of H₂O also has a positive effect on both NO_x concentration and energy cost. Optical emission spectrum (OES) shows that air?+?H₂O plasma has stronger 336 nm (NH) and 309 nm (OH) emission lines than air plasma, suggests NH and OH are the key species in NO_x enhancement. The most energy efficient conditions are found at airflow rate of 15 l min^?1, 12% H₂O concentration, with 4 blades on each rotating speed. Under these conditions, the lowest energy cost is observed to be 165 GJ/tN.

     

Kinetics and nitro-products of the gas-phase OH and NO3 radical-initiated reactions of naphthalene-d8, Fluoranthene-d10, and pyrene

The kinetics and nitroarene product yields of the gas-phase reactions of naphthalene-d₈, fluoranthene-d₁₀, and pyrene with OH radicals in the presence of NO_x and in N₂O₅? NO₃? NO₂? air mixtures have been investigated at 296 ± 2 K and atmospheric pressure of air. Using a relative rate method, naphthalene-d₈ was shown to react in N₂O₅? NO₃? NO₂? air mixtures a factor of 1.22 ± 0.10 times faster than did naphthalene, with the 1- and 2-nitronaphthalene-d₇ product yields being similar to those of 1- and 2-nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2-, 7-, and 8-nitrofluoranthene-d₉ and 2- and 4-nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical-initiated reactions. Effective rate constants for the reactions of fluoranthene-d₁₀ and pyrene with N₂O₅ in N₂O₅? ;NO₃? NO₂? air mixtures of ca. 1.8 × 10^?17 cm³ molecule^?1 s^?1 and ca. 5.6 × 10^?17 cm³ molecule^?1 s^?1, respectively, were derived. Formation yields of 2-nitrofluoranthene-d₉ and 4-nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2-Nitropyrene was also observed to be formed in these N₂O₅? NO₃? NO₂ reactions, but was found to be a function of the NO₂ concentration and, therefore, would be a negligible product under ambient NO₂ concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations.     

Reactions of naphthalene in N2O5?NO3?NO2? air mixtures

The reactions of naphthalene in N₂O₅? NO₃? NO₂? N₂? O₂ reactant mixtures have been investigated over the temperature range 272–297 K at ca. 745 torr total pressure and at 272 K and ca. 65 torr total pressure using long pathlength Fourier transform infrared absorption spectroscopy. 2,3-Dimethyl-2-butene was added to the reactant mixtures at 272 K to rapidly scavenge the NO₃ radicals both initially present in the added N₂O₅ and formed from the thermal decomposition of N₂O₅ during the reactions. The data obtained in the presence and absence of added 2,3-dimethyl-2-butene showed that napthalene undergoes initial reaction with the NO₃ radical to form an NO₃-naphthalene adduct, which either rapidly decomposes back to the reactants (at a rate of ca. 5 × 10⁵ s^?1 at 298 K) or reacts exclusively with NO₂ to form products. When NO₃ radicals, N₂O₅ and NO₂ are in equilibrium, this overall process is kinetically equivalent to reaction of naphthalene with N₂O₅, and previous kinetic and product studies have indeed assumed the reactions of naphthalene and alkyl-substituted naphthalenes in N₂O₅? NO₃? NO₂? air mixtures to be with N₂O₅, and not with NO₃ radicals.     

Formation of peroxynitrite induced by spark plasma radiation

The formation of peroxynitrite (ONOO^?) in water by the action of plasma UV radiation from spark discharge in air has been studied. Solutions with pH₀ 3.11–12.86 have been treated. In all cases, the pH has been observed to decrease immediately after the treatment and for the following 14 days. An absorption line characteristic of peroxynitrite (λ = 302 nm) appears in the spectrum by the fourth to fifth day after the treatment and reaches a maximum by the 10th–12th day. The appearance of peroxynitrite a few days after the treatment can be caused by the formation of a substance X during a radiation pulse at a high density of active species, which decomposes according to the scheme X → ONOO^? → NO ₃ ^? and has a lifetime of about 10 days. The maximal yield of peroxynitrite is (1.2 ± 0.5) × 10^?2 mol/L.     

Coulomb explosion dynamics of N2O in intense laser-field: Identification of new two-body and three-body fragmentation pathways

The Coulomb explosion process of N₂O in an intense laser-field (∼5 PW/cm²) has been investigated by the high-resolution time-of-flight (TOF) spectroscopy. Six two-body explosion pathways involving the NO⁺, NO²⁺, N₂ ⁺ molecular ions have been securely identified from the momentum-scaled TOF spectra of the fragment ions. Assuming a linear geometry, three-body explosion pathways were investigated by sequential and concerted explosion models. When the concerted model is adopted, the observed momentum distributions of six atomic ion channels; N⁺, N²⁺, N³⁺, O⁺, O²⁺ and O³⁺, were well fitted using the Gaussian momentum distribution with the optimized bond elongation factor of 2.2(3). From the yields of individual Coulomb explosion pathways determined by the fit, the abundance of the parent ions, N₂O^z+ (z=2–8), prior to the two- body and three-body explosion processes was found to have a smooth distribution with a maximum at z∼3.     

Hemoglobin as a nitrite anhydrase: modeling methemoglobin-mediated N2O3 formation

Nitrite has recently been recognized as a storage form of NO in blood and as playing a key role in hypoxic vasodilation. The nitrite ion is readily reduced to NO by hemoglobin in red blood cells, which, as it happens, also presents a conundrum. Given NO’s enormous affinity for ferrous heme, a key question concerns how it escapes capture by hemoglobin as it diffuses out of the red cells and to the endothelium, where vasodilation takes place. Dinitrogen trioxide (N₂O₃) has been proposed as a vehicle that transports NO to the endothelium, where it dissociates to NO and NO₂. Although N₂O₃ formation might be readily explained by the reaction Hb‐Fe³⁺+NO₂^?+NO?Hb‐Fe²⁺+N₂O₃, the exact manner in which methemoglobin (Hb‐Fe³⁺), nitrite and NO interact with one another is unclear. Both an “Hb‐Fe³⁺‐NO₂^?+NO” pathway and an “Hb‐Fe³⁺‐NO+NO₂^?” pathway have been proposed. Neither pathway has been established experimentally. Nor has there been any attempt until now to theoretically model N₂O₃ formation, the so‐called nitrite anhydrase reaction. Both pathways have been examined here in a detailed density functional theory (DFT, B3LYP/TZP) study and both have been found to be feasible based on energetics criteria. Modeling the “Hb‐Fe³⁺‐NO₂^?+NO” pathway proved complex. Not only are multiple linkage‐isomeric (N‐ and O‐coordinated) structures conceivable for methemoglobin–nitrite, multiple isomeric forms are also possible for N₂O₃ (the lowest‐energy state has an N? N‐bonded nitronitrosyl structure, O₂N? NO). We considered multiple spin states of methemoglobin–nitrite as well as ferromagnetic and antiferromagnetic coupling of the Fe³⁺ and NO spins. Together, the isomerism and spin variables result in a diabolically complex combinatorial space of reaction pathways. Fortunately, transition states could be successfully calculated for the vast majority of these reaction channels, both M_S=0 and M_S=1. For a six‐coordinate Fe³⁺‐O‐nitrito starting geometry, which is plausible for methemoglobin–nitrite, we found that N₂O₃ formation entails barriers of about 17–20 kcal mol^?1, which is reasonable for a physiologically relevant reaction. For the “Hb‐Fe³⁺‐NO+NO₂^?” pathway, which was also found to be energetically reasonable, our calculations indicate a two‐step mechanism. The first step involves transfer of an electron from NO₂^? to the Fe³⁺–heme–NO center ({FeNO}⁶) , resulting in formation of nitrogen dioxide and an Fe²⁺–heme–NO center ({FeNO}⁷). Subsequent formation of N₂O₃ entails a barrier of only 8.1 kcal mol^?1. From an energetics point of view, the nitrite anhydrase reaction thus is a reasonable proposition. Although it is tempting to interpret our results as favoring the “{FeNO}⁶+NO₂^?” pathway over the “Fe³⁺‐nitrite+NO” pathway, both pathways should be considered energetically reasonable for a biological reaction and it seems inadvisable to favor a unique reaction channel based solely on quantum chemical modeling.     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

VUV photolysis of aqueous solutions of nitrate and nitrite

Water homolyses upon vacuum-uv excitation into HO^* radicals, hydrogen atoms and with lower efficiency, hydrated electrons. These primary species induce a series of reactions partially depleting nitrate and nitrite from aqueous solutions. Depletion rates depend on the presence of dissolved oxygen and temperature. Nitrate, nitrite, peroxynitrite and N₂O were identified as reaction products after irradiation of, either, nitrite and nitrate in aqueous solutions. A reaction mechanism is proposed in accord with the experimental facts and with the evidence given in the literature, where NO₂ ^* and NO^* are key intermediates. NO₃ ^?, NO₂ ^?, NO₂ ^*, NO^* O₂NO₂ ^?, ONO₂ ^? and N₂O, seem to be interrelated by many redox reactions and reaction equilibria where pH and the availability of electrons determine their occurrence. The proposed mechanism is supported by a computer program with which the observed experimental behavior could be simulated.     

Contrasting chemiluminescent metal oxide formation: In the single collision reactions of boron with O2, NO2, N2O,O3 and ClO2

An intense source has been developed to study the reactions of boron (²P) atoms with O₂, NO₂, N₂O, ClO₂, and O₃. The chemiluminescent emissions which characterize the bimolecular reaction of boron with O₂, N₂O, ClO₂, and O₃ are dominated by the A ²Π-X ²Σ⁺ band system of BO. In contrast the chemiluminescence from the boron- NO₂ reaction is dominated by strong BO₂ A ²Π_u-X ²Σ_g emission.     

The reactions of isotopically labeled N15NO+ with CO,NO, O2, N2, NO2, and N2O

The reactions of labeled N¹⁵NO⁺ with CO, NO, O₂, ¹⁸O₂, N₂, NO₂, and N₂O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.     

The electronic structure of N4O62+ and the bonding interaction of NO+ and NO3−

The results are reported of an MO-SCF-CNDO/2 study of the experimental and optimal geometries of the N₄O₆²⁺ion cluster. The calculations are shown to support the stable existence of the N₄O₆²⁺ complex and the suggestion of its discoverers [1] on the role of NO⁺ in the N₂O₄ solutions. The proposed interpretation of the bonding interaction explains why the shortest N β O distances are found with the NO⁺ ions which have their nitrogen atoms displaced out of the NO₃^? plane.     

Nitrosonium Nitrate,an Isomer of N2O4 in IF5

N₂O₄ dissolves in IF₅ as NO⁺NO₃^–, as established by n.m.r spectroscopy, and in the solid state the solvate complex NO⁺NO₃^– · IF₅ is formed. This contains a double chain of alternating NO⁺ cations and NO₃^– anions. (a = 483.4(2), b = 773.9(1), c = 932.6(3) pm, (α = 70.18(2)°, β = 80.90(3)°, (γ = 87.34(2)°, space group P1, Z = 2).     

The Distribution of Charge in Complex Compounds

The charges on metal atoms and ligands in complex compounds of transition metals may be calculated theoretically or measured empirically, but there is no reliable method of doing either. This review is concerned mainly with two experimental methods, dipole moment measurement and X-ray photoelectron spectroscopy, applied to tertiary phosphate and such complexes of the heavier transition metals. It is concluded that the charge is rarely greater than ±0.3e and that some so-called neutral or positive ligands, e.g. N₂ or NO⁺, may carry more negative charge in a complex than formally anionic ligands such as H^?. Small ligands of high formal charge, e.g. O^2?, NR^2?, and N^3?, appear to carry no more negative charge than Cl^?, but monoanionic ligands vary greatly in their capacity to contribute to the dipole moments. The ligands NO, CO, PF₃, CH, and H^? are all nearly neutral to slightly negative, whereas pyridines, tertiary phosphanes, etc. are the most strongly positively charged.     

A [Fe(CB6)] platform for binding of small molecules: Insights from DFT calculations

The viability of making [Fe(CB₆)L] (L = H₂, N₂, O₂, nitric oxide [NO^?, NO, and NO⁺], CO₂, and hydrocarbons [CH₄, C₂H₆, C₂H₄, and C₆H₆]) has been investigated by density functional theory (DFT) calculations. The complexes 2 – 18 are thermodynamically stable and may be synthesized. The small molecules are activated to some extent after complexation. Molecular orbital and ΔG calculation revealed that the molecular hydrogen and hydrocarbons can be chemically adsorbed and desorbed on [Fe(CB₆)] without any significant chemical modification and therefore [Fe(CB₆)] may serve as a storage material. The N₂, O₂, and nitric oxide (NO^?, NO, and NO⁺) can be activated using [Fe(CB₆)]. Proton, carbon, boron, and nitrogen NMR chemical shift calculation predicts drastic chemical shift difference before and after the complexation of [Fe(CB₆)] with small molecules. This new findings suggest that the CB₆^2? ligand‐based complex may provide several applications in the future. © 2012 Wiley Periodicals, Inc.