Identification of Thermal Decomposition Products and Reactions for Liquid Ammonium Nitrate on the Basis of Ab Initio Calculation

This work analyzed the thermal decomposition of ammonium nitrate (AN) in the liquid phase, using computations based on quantum mechanics to confirm the identity of the products observed in past experimental studies. During these ab initio calculations, the CBS‐QB3//ωB97XD/6–311++G(d,p) method was employed. It was found that one of the most reasonable reaction pathways is HNO₃ + NH₄⁺ → NH₃NO₂⁺ + H₂O followed by NH₃NO₂⁺ + NO₃^– → NH₂NO₂ + HNO₃. In the case in which HNO₃ accumulates in the molten AN, alternate reactions producing NH₂NO₂ are HNO₃ + HNO₃ → N₂O₅ + H₂O and subsequently N₂O₅ + NH₄⁺ → NH₂NO₂ + H₂O. In both scenarios, HNO₃ plays the role of a catalyst and the overall reaction can be written as NH₄⁺ + NO₃^– (AN) → NH₂NO₂ + H₂O. Although the unimolecular decomposition of NH₂NO₂ is thermodynamically unfavorable, water and bases both promote the decomposition of this molecule to N₂O and H₂O. Thus AN thermal decomposition in the liquid phase can be summarized as NH₄⁺ + NO₃^– (AN) → N₂O + 2H₂O.     

Reactivity of Semivolatile Organic Compounds with Hydroxyl Radicals,Nitrate Radicals,and Ozone in Indoor Air

Indoor semivolatile organic compounds (SVOCs) originate from indoor and outdoor sources. These SVOCs partition among different phases and available surfaces, which increases their residence time indoors to several years. SVOCs may also react with indoor oxidants, such as hydroxyl radicals (OH), nitrate radicals (NO₃), and ozone. In the present study, the second‐order reaction rate constants of 72 SVOCs in indoor air (gas and particle phases) at room temperature and ambient air pressure were retrieved from the literature. The pseudo–first‐order reaction rate constants of these SVOCs were calculated for the indoor concentration ranges of OH, NO₃, and ozone. Then, the extent to which the chemical reaction had a meaningful impact on the removal of SVOCs from the indoor environment was quantitatively analyzed. The orders of magnitude of the second‐order rate constant ranged between 10⁻¹⁵ and 10⁻¹⁰ cm³/(molecule·s) for OH/SVOC reactions, 10⁻¹⁷ and 10⁻¹² cm³/(molecule·s) for NO₃/SVOC reactions, and 10⁻²⁰ and 10⁻¹⁶ cm³/(molecule·s) for ozone/SVOC reactions in indoor air. Assuming that the highest indoor reactant concentrations were 1.8 × 10⁶ molecules/cm³ (7.3 × 10⁻⁵ ppb) for OH, 2.5 × 10⁸ molecules/cm³ (10⁻² ppb) for NO₃, and 1.4 × 10¹² molecules/cm³ (58 ppb) for ozone, the highest pseudo–first‐order rate constants in the gas phase for the studied reactions of OH/SVOCs (n = 72), NO₃/SVOCs (n = 3), and ozone/SVOCs (n = 14) reached 1.5 h⁻¹ (OH/benzo[a]pyrene), 0.41 h⁻¹ (NO₃/acenaphthene), and 1.0 h⁻¹ (ozone/aldrin and ozone/heptachlor), respectively. The pseudo–first‐order rate constants in the particle phase for the studied reactions of OH/SVOCs (n = 13), NO₃/SVOCs (n = 6), and ozone/SVOCs (n = 14) at the high indoor reactant concentrations reached 0.09 h⁻¹ (OH/DEHP), 5.8 h⁻¹ (NO₃/pyrene), and 11 h⁻¹ (ozone/benzo[a ]pyrene), respectively. These results indicate that the chemical reactions of some SVOCs in indoor air have a meaningful impact compared to the air exchange rate, which should be considered in future studies on indoor air quality modeling.     

Experimental determination of the mean ionization energy in nitrogen oxides in a <Superscript>60</Superscript>Co γ-radiation field

The mean energy of ion pair formation in O₂, N₂, CO₂, air, N₂O, NO, and NO₂ was experimentally determined. Verification of the procedure for determining the work of ionization from calculated stopping powers and ionization measurement data showed good agreement with published data. The mean energy of ion pair formation in NO (31.6 ± 0.1 eV) and NO₂ (31.3 ± 0.2 eV) was determined for the first time.     

Transient Spark Discharge Generated in Various N2/O2 Gas Mixtures: Reactive Species in the Gas and Water and Their Antibacterial Effects

Reactive species generated in the gas and in water by cold air plasma of the transient spark discharge in various N₂/O₂ gas mixtures (including pure N₂ and pure O₂) have been examined. The discharge was operated without/with circulated water driven down the inclined grounded electrode. Without water, NO and NO₂ are typically produced with maximum concentrations at 50% O₂. N₂O was also present for low O₂ contents (up to 20%), while O₃ was generated only in pure O₂. With water, gaseous NO and NO₂ concentrations were lower, N₂O was completely suppressed and HNO₂ increased; and O₃ was lowered in O₂ gas. All species production decreased with the gas flow rate increasing from 0.5 to 2.2 L/min. Liquid phase species (H₂O₂, NO₂￣, NO₃￣, ^·OH) were detected in plasma treated water. H₂O₂ reached the highest concentrations in pure N₂ and O₂. On the other hand, nitrites NO₂￣ and nitrates NO₃￣ peaked between 20 and 80% O₂ and were associated with pH reduction. The concentrations of all species increased with the plasma treatment time. Aqueous ^·OH radicals were analyzed by terephthalic acid fluorescence and their concentration correlated with H₂O₂. The antibacterial efficacy of the transient spark on bacteria in water increased with water treatment time and was found the strongest in the air-like mixture thanks to the peroxynitrite formation. Yet, significant antibacterial effects were found even in pure N₂ and in pure O₂ most likely due to high ^·OH radical concentrations. Controlling the N₂/O₂ ratio in the gas mixture, gas flow rate, and water treatment time enables tuning the antibacterial efficacy.

     

Concentrations of active species in a bulk barrier discharge in a plasmochemical reactor

The results of theoretical and experimental studies of the chemical composition of the ensemble of active species formed in a plasmochemical reactor that consists of a multicell bulk-barrier-discharge generator of active species and a working chamber are presented. To calculate the composition of the neutral species in the barrier discharge, an approach based on the averaging of the power input over the entire volume of the discharge gap was proposed. One advantage of this approach is that it involves no adjustable parameters, such as the sizes of the microdischarges, their surface density, and frequency of breakdowns. The calculations and measurements were performed using dry air (with a relative humidity of 20%) as the plasma-forming medium. The concentrations of O₃, HNO₃, HNO₂, N₂O₅, and NO₃ in the discharge gap and working chamber were measured at a mean residence time of the species in the discharge gap of τ = 0.3 s and a specific power input of 1.5 W/cm³. The best agreement between the calculation results and the experimental data was obtained when the temperature of the gas mixture in the discharge was set equal to 400–425 K, a value that coincided with the measured rotational temperature of molecular nitrogen. Generally, the calculated and measured concentrations of O₃, HNO₃, HNO₂, N₂O₅, and NO₃ in both the bulk barrier discharge and the working chamber were found to be in close agreement.     

Linear-Reactor-IR.-Matrix and Microwave Spectroscopy of the System O3/NO2/(Z)-2-Butene

Investigation of the formation of complex reaction products in the gas-phase system O₃/NO₂/(Z)-2-butene by combination of linear reactors with IR. matrix and microwave Stark Spectroscopy is reported. Besides the polyatomic products observed earlier in the gas-phase ozonolysis of (Z)-2-butene, the following products were identified; N₂O₅, HNO₃, HNO₄, CH₃NO₂, CH₃ONO, CH₃COONO₂ and CH₃COO₂NO₂ (peroxyacetyl nitrate, PAN). Matrix IR. spectra of N₂O₅, HNO₃. CH₃COONO, CH₃COONO₂ required for reference purposes are presented. It is shown that PAN-formation occurs already in the absence of light. A reaction scheme is proposed for explanation of the observed complex NO_x-containing products, which assumes methyldioxirane as a central intermediate. Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies.     

Optical detection of NO3 and NO2 in “pure” HNO3 vapor,the liquid-phase decomposition of HNO3

Flowing and static gas-phase samples of HNO₃ in O₂ and N₂ were analyzed by long-path ultraviolet/visible (UV/VIS) spectroscopy to reveal the presence of both NO₂ and NO₃, the concentrations of which were calculated using differential absorption cross sections. NO₂ is produced predominantly by the heterogeneous decomposition of HNO₃, whereas NO₃ is generated in the gas phase by the thermal decomposition of N₂O₅, a product of the self-disproportionation of liquid HNO₃. © 1993 John Wiley & Sons, Inc.     

A kinetic study of the decomposition of HNO3 and its reaction with NO

The rate of reaction between NO and HNO₃ and the rate of thermal decomposition of HNO₃ have been measured by FTIR spectroscopy. The measurements were made in a teflon lined batch reactor having a surface to volume ratio of 14 m^?1. During the experiments, with initial HNO₃ concentrations between 2 and 12 ppm and NO concentrations between 2 and 30 ppm, a reactant stoichiometry of unity and a first order NO and HNO₃ dependence were confirmed. The observed rate constant for the reaction at 22°C and atmospheric pressure was determined to 1.1 (±0.3) 10^?5 ppm^?1 min^?1. At atmospheric pressure, HNO₃ decomposes into NO₂ and other products with a first order HNO₃ dependence and with a rate constant of 2.0 (±0.2) 10^?3 min^?1. The apparent activation energy for the decomposition is 13 (±4) kJ mol^?1.     

Modeling Chemical Composition for an Atmospheric Pressure DC Discharge in Air with Water Cathode by 0-D model

This paper reports the results of the chemical composition modeling for an atmospheric pressure DC air discharge with water cathode. The modeling was based on the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N₂, O₂, H₂O and NO molecules, equations of chemical kinetics and plasma conductivity equation. Calculations were carried out using experimental values of E/N and gas temperatures for the discharge currents range of 20–50 mA. The effect of H₂O concentration on the plasma composition was studied. The main particles of plasma were shown to be O₂(a¹Δ, b¹Σ), O(³P), NO, NO₂, HNO₃, H₂O₂ and OH. Effective vibrational temperatures of molecules were higher than gas temperature and they did not depend on the discharge current. Distribution functions on vibrational levels for N₂, O₂, H₂O and NO ground states were non-equilibrium ones.     

Chlorine nitrate photolysis by a new technique: very low pressure photolysis

Very low pressure photolysis (VLPØ) of chlorine nitrate was performed in a quartz Knudsen cell. The light source was a 2500 W high-pressure xenon lamp, and a modulated molecular-beam mass spectrometer was used to monitor the concentration of ClONO₂ and photolysis products. Because of the low pressures used (? 10^?3 torr) and the short residence time in the cell (≈1 s), secondary reactions were unimportant and the primary products could be directly identified. The primary photolysis products (λ ≈ 2700 Å) are atomic chlorine and NO₃ free radical. Chlorine atoms were identified both by the appearance of Cl₂ (wall recombination product; the walls were not poisoned) and by HCl produced when C₂H₆ was added to the cell. Nitrate free radical was directly identified as a mass peak at m/e = 62, as well as by chemical titration with nitric oxide: NO₃ + NO → 2NO₂. It was verified by direct tests that the peak at m/e = 62 did not arise from possible HNO₃ contamination or from N₂O₅, a possible secondary product. This titration reaction was used to measure quantitatively a lower limit to the primary quantum yield, φ ? 0.5 ± 0.3. This represents a lower limit because of the unknown extent of the secondary photolysis of NO₃ under our conditions. We believe this to be the first observation using mass spectrometry of the NO₃ free radical. The quantum yield for atomic chlorine is φ = 1.0 ± 0.2. N₂O was used to test for O(¹D) according to the reaction, O(¹D) + N₂O → products; none was observed. Triplet oxygen, O(³P) was observed to the extent of ≈ 10% by the reaction O(³P) + NO₂ → NO + O₂, but this yield can also be due to the photolysis of NO₃ free radical produced in the primary step. We conclude that the predominant reaction pathway is

.     

The thermal decomposition of the new energetic material ammoniumdinitramide (NH4N(NO2)2) in relation to Nitramide (NH2NO2) and NH4NO3

This qualitative study examines the response of the novel energetic material ammonium dinitramide (ADN), NH₄N(NO₂)₂, to thermal stress under low heating rate conditions in a new experimental apparatus. It involved a combination of residual gas mass spectrometry and FTIR absorption spectroscopy of a thin cryogenic condensate film resulting from deposition of ADN pyrolysis products on a KCl window. The results of ADN pyrolysis were compared under similar conditions with the behavior of NH₄NO₃ and NH₂NO₂ (nitramide), which served as reference materials. NH₄NO₃ decomposes into HNO₃ and NH₃ at 182°C and is regenerated on the cold cryostat surface. HNO₃ undergoes presumably heterogeneous loss to a minor extent such that the condensed film of NH₄NO₃ contains occluded NH₃. Nitramide undergoes efficient heterogeneous decomposition to N₂O and H₂O even at ambient temperature so that pyrolysis experiments at higher temperatures were not possible. However, the presence of nitramide can be monitored by mass spectrometry at its molecular ion (m/? 62). ADN pyrolysis is dominated by decomposition into NH₃ and HN(NO₂)₂ (HDN) in analogy to NH₄NO₃, with a maximum rate of decomposition under our conditions at approximately 155°C. The two vapor phase components regenerate ADN on the cold cryostat surface in addition to deposition of the pure acid HDN and H₂O. Condensed phase HDN is found to be stable for indefinite periods of time at ambient temperature and vacuum conditions, whereas fast heterogeneous decomposition of HDN at higher temperature leads to N₂O and HNO₃. The HNO₃ then undergoes fast (heterogeneous) decomposition in some experiments. Gas phase HDN also undergoes fast heterogeneous decomposition to NO and other products, probably on the internal surface (ca. 60°C) of the vacuum chamber before mass spectrometric detection. © 1993 John Wiley & Sons, Inc.     

Reduction of nitric oxide,nitrous acid and nitrogen dioxide at platinum electrodes in acidic solutions: Review and new voltammetric results

The literature concerning the chemical and electrochemical reactions of nitric oxide, nitrous acid and nitrogen dioxide in aqueous solutions is reviewed briefly, with emphasis on electrochemical reductions at platinum electrodes in acidic solutions. The voltammetric behavior of NO and NO₂ at a Pt electrode in perchloric acid is virtually identical to that for HNO₂ and this is explained on the basis of a common electroactive precursor concluded to be NO⁺. Three cathodic waves are obtained for acidic solutions of NO, HNO₂ and NO₂. The first two waves correspond to reduction of NO⁺ to NO and N₂O₃ to NO, respectively. The presence of N₂O₃ results from decomposition of the parent compounds. The presence of Br^- or Cl^- in acidic solutions of the title compounds promotes the voltammetric reductions at lower H⁺ concentrations. This probably results from formation of electroactive nitrosyl halides.     

Rate constants for: OH + NO2 (+ N2) → HNO3 (+ N2) between 220 and 358 K

Rate constants have been determined for the reaction OH + NO₂ (+ N₂) → HNO₃ (+ N₂), using time-resolved resonance absorption to follow the removal of OH radicals produced by flash photolysis of HNO₃. The measurements cover the ranges: 220 ? T ? 358 K and 3.2 × 10¹⁷ ? [N₂] ? 4.0 × 10¹⁸ molecule cm^?3.     

Lanthanon (III) Complexes of Bifunctional Tridentate and Tetradentate Schiff Bases

Reactions of isopropoxides of praseodymium, neodymium and samarium with bifunctional tridentate and tetradentate schiff bases (i.e. salicylidene-O-aminophenol and bis-salicylaldehyde ethylenediamine) have been carried out in benzene in different stoichiometric ratios resulting in the formation of products with the formula M(OPrⁱ)(C₁₁H₉NO₂), M(C₁₃H₉NO₂)(C₁₃H₁₀NO₂). M₂(C₁₃H₉NO₂) M(OPrⁱ)(C₁₅H₁₄N₂O₂), M(C₁₆H₁₄N₂O₂)(C₁₆H₁₅N₂O₂) and M₂(C₁₆H₁₄N₂O₂)₃ (where M stands for Pr, Nd and Sm). The products were found to be yellow to orange solids soluble in benzene and alcohol. The absorption spectra of these complexes were also recorded in methanol.     

Mass spectrometric in-situ determination of NO2 in gas mixtures by resonance enhanced multiphoton ionisation

One- and two-colour photoionisation spectra for NO₂ have been investigated using a time of flight mass spectrometer as detector to find the most efficient REMPI process for analytical applications. Two different inlet systems have been employed: a pulsed supersonic jet expansion stage and a flow reactor. Selective and sensitive mass spectrometric determinations of free NO₂ have been possible even in the presence of high concentrations of organic nitrates, HNO₃ and other NO₂ precursors. Employing two-colour (1+1′+1) excitation using a concentration of HNO₃≤5·10¹⁴ molecules/cm³ a detection limit of 5·10¹¹ molecules/cm³ has been found for NO₂ whereas in the absence of HNO₃ a detection limit of 5·10¹⁰ molecules/cm³ is reported.     

Synthesis and Characterization of Solid Coordination Complexes of Diamides for Uranium(VI) and Thorium(IV)

Five kinds of solid coordination complexes of uranium(VI) and thorium(IV) with the diamide (N,N,N,N-tetrabutylmalon-amide (TBMA), N,N,N,N-tetrabutylsuccinylamide (TBSA), N,N,N,N-tetrabutylglutaramide (TBGA), N,N,N,N-tetrabutyl-adipicamide (TBAA)) were synthesized. All these complexes of UO₂(NO₃)₂·TBMA, UO₂(NO₃)₂· TBSA, [UO₂(NO₃)₂·(TBGA^1/2)₂] _x , UO₂(NO₃)₂·TBAA and Th(NO₃)₄·2TBMA were characterized by elemental analysis, UV spectra, IR spectra and ¹³C NMR spectra. The coordination form and proposed structures of the complexes are also discussed.     

Ozone synthesis in charged particle induced noble gas-oxygen and noble gas-oxygen-sulfur hexafluoride discharges

A series of experimental measurements of ozone concentration produced by irradiation of noble gas (He, Ne, and Ar)-O₂ and noble gas-O₂-SF₆ mixtures with energetic (MeV) helium and lithium ions are reported. Continuous irradiations at dose rates of 10¹⁵–10¹⁷ eV cm ^–3 s ^–1 for a few hundred milliseconds were used. The resulting ozone concentration was found to be nonlinear with dose rate for a given irradiation time. This nonlinearity was effectively reduced by an increase in noble gas pressure. Few mole percent addition of SF₆ generally resulted in an increase in the ozone concentration. This increase was highest for lower noble gas pressures and longer irradiation times. Further SF₆ addition, however, caused a reduction in the ozone concentration. Results are explained by considering the relevant reactions responsible for ozone production and loss.     

Investigation of the gas phase reaction of dinitrogen pentoxide with water vapor

The gas phase reaction of N₂O₅ with water vapor was investigated in a 17.3-m³ Teflon lined chamber. Temporal concentration profiles for ozone, total nitrogen oxides, and nitrogen dioxide were measured. Concentration profiles for N₂O₅ and HNO₃ were calculated from a combination of measurements of nitrogenous species. A kinetic mechanism with an adjustable value for the rate constant of N₂O₅ + H₂O was used to model the experiments. From this analysis an upper limit value of k ? 4 × 10^?7 ppm^?1 min^?1 for the gas phase reaction N₂O₅ + H₂O → 2HNO₃ was derived.     

Photocatalytic removal of nitrogen oxides from air on TiO<Subscript>2</Subscript> modified with bases and platinum

The efficiency of TiO₂ (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O₂ + N₂ mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO₂, NO₃⁻), it is impossible to realize prolonged continuous removal of NO _x (NO + NO₂) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NO _x adsorbed during 2-h-long irradiation. Modification of TiO₂ with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO₂ and NO₃⁻. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO₂. The SPC of the (0.5% Pt)/TiO₂ catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt⁺ and Pt²⁺, have an approximately 2 times higher SPC than unpromoted TiO₂ and ensure a much larger NO₂/NO ratio at the reactor outlet. Conversely, the samples reduced in an H₂ atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO₂ and cause no significant change in the NO₂/NO ratio.     

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.