Kinetics and thermodynamics of reversible disproportionation–comproportionation in redox triad oxoammonium cations – nitroxyl radicals – hydroxylamines

Kinetics and equilibrium of the acid‐catalyzed disproportionation of cyclic nitroxyl radicals R₂NO^? to oxoammonium cations R₂NO⁺ and hydroxylamines R₂NOH is defined by redox and acid–base properties of these compounds. In a recent work (J. Phys. Org. Chem. 2014, 27, 114‐120), we showed that the kinetic stability of R₂NO^? in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R₂NO⁺ and R₂NOH to R₂NO^? and found that increasing in –I‐effects of substituents greatly reduces the overall equilibrium constant of the reaction K₄. This occurs because of both the increase of acidity constants of hydroxyammonium cations K_3H+ and the difference between the reduction potentials of oxoammonium cations E_R2NO+/R2NO? and nitroxyl radicals E_R2NO?/R2NOH. pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E_1/3Σ and bond dissociation energies D(O–H) for hydroxylamines R₂NOH in water were determined. For a wide variety of piperidine‐ and pyrrolidine‐1‐oxyls values of pK_3H+ and E_R2NO+/R2NO? correlate with each other, as well as with the equilibrium constants K₄ and the inductive substituent constants σ_I. The correlations obtained allow prediction of the acid–base and redox characteristics of redox triads R₂NO^?–R₂NO⁺–R₂NOH. Copyright © 2014 John Wiley & Sons, Ltd.     

Pyrolysis synthesis of magnetic - and -MnO2 nanostructures and the polymorph discrimination

The concentration of the Mn(NO₃)₂ solution has significant influence on the morphologies and the phases of the MnO₂ products. A large number of ε- MnO₂ nanowires were prepared via a simple pyrolysis under lower reaction concentration. The nanowires have lengths up to tens of micrometers and diameters in the range of 20–100 nm. The β- MnO₂ nanobundles and nanoflowers were prepared by increasing the concentration of Mn(NO₃)₂ solution. The superparamagnetism of ε- MnO₂ nanowires and paramagnetism of β- MnO₂ nanoflowers indicate their potential applications in magnetic materials.     

Adsorption of pairs of NOx molecules on single-walled carbon nanotubes and formation of NO + NO3 from NO2

The adsorption of NO_x(x = 1, 2, 3) molecules on single-walled carbon nanotubes (SWCNTs) is investigated using first-principle calculations. Single NO, NO₂ and NO₃ molecules are found to physisorb on SWCNTs, but molecules can be chemisorbed in pairs on the top of carbon atoms at close sites of SWCNTs. The adsorption energy for pairs of NO or NO₃ molecules is larger than for pairs of NO₂ molecules. The local curvature is found to have a sizable effect on adsorption energies. The possibility of a surface reaction NO₂ + NO₂ → NO + NO₃ is examined and the relative pathway and barrier is calculated. The results are discussed with reference to available experimental results.     

Suppression of the shear viscosity near the critical temperature in hot QCD

We consider QCD near but above critical temperature T_c. The pressure, susceptibilities and the renormalized Polyakov loop — which is an order parameter for the deconfining phase transition — dramatically change up to temperatures a few times T_c. We refer to this region as a “semi”-QGP, where partial confinement plays important role. We show that the shear viscosity η is suppressed by two powers of the Polyakov loop. This suggests that η/T³ decreases markedly as QCD cools down to temperatures near T_c. We also show a ratio of the viscosity to the entropy becomes small near T_c [Y. Hidaka and R.D. Pisarski, Phase," arXiv:0803.0453 [Phys. Rev. D (to be published)]].     

ATMOSPHERIC REMOTE-SENSING REFERENCE DATA FROM GOME: PART 1. TEMPERATURE-DEPENDENT ABSORPTION CROSS-SECTIONS OF NO2 IN THE 231–794 nm RANGE

Absorption cross-sections of NO₂ between 231–794 nm have been measured in the 221–293 K temperature range, using the global ozone monitoring experiment (GOME) flight-model (FM) satellite spectrometer. The spectra have a resolution of about 0.2 nm below 400 nm and of about 0.3 nm above 400 nm. These are the first reference spectra of NO₂ covering at the same time the entire UV–visible–NIR spectral range and a broad range of relevant atmospheric temperatures. The new absorption cross-sections are important as accurate reference data for atmospheric remote-sensing of NO₂ and other minor trace gases.     

Spectroscopic Study of DHDA Complex Formation of d- and f-Electron Metal Ions in Methanol Solution

Synthesis and spectral characterization of N,N′-Bis(2,4-dihydroxobenzylidene)1,2-diaminobenzene (DHDA) complexes with chosen f- and d-metal ions are described. Physico-chemical properties of a series of complexes: DHDA–La(NO₃)₃, DHDA–Eu(NO₃)₃. DHDA–Yb(NO₃)₃, DHDA–Cu(NO₃)₂, DHDA–Zn(NO₃)₂, DHDA–Co(NO₃)₂, were studied in methanol solution using UV-VIS, IR and fluorescence spectroscopy. Based on the absorption spectra the conditional stability constants of the metal complexes were determined.     

Measurements of line intensities and determination of transition moment parameters from experimental data for the ν1 and ν3 bands of D2S

First measurements of line intensities for ν₁ and ν₃ bands of D₂³²S are reported. About 300 intensities of D₂³²S vibration–rotation lines were obtained from experimental high-resolution spectra recorded in the 1810–2051 cm⁻¹ region with the Fourier Transform Spectrometer built in Reims. Empirical values of transition moment parameters for ν₁ and ν₃ bands of D₂³²S were determined for the first time using a least-square fit to the observed intensities. Experimental D₂³²S intensities were compared with recent global variational predictions [Vl.G. Tyuterev, L. Régalia-Jarlot, D.W. Schwenke, S.A. Tashkun, Y.G. Borkov, C. R. Phys. 5 (2004) 189–199] computed from isotopically invariant potential and dipole moment functions of the hydrogen sulphide molecule. Average discrepancy between these calculations and our observed data was 0.03 cm⁻¹ for line positions of this spectral range. The discrepancy between these calculations and our measurements for the sum of line intensities was 5.5% and 3.5% for the ν₁ and ν₃ bands, correspondingly.     

NOx generation in laser-produced plasma in air as a function of dissipated energy

An experimental study on the production of NO_x as a function of dissipated energy in laser-produced plasma in air is presented. A plasma was produced by focusing a (60–180) mJ, 5 ns, 532 nm pulse from a Q-switched Nd:YAG laser. The results show that for laser energy in the range of 13–99 mJ the laser plasma generates 6.7×10¹⁶ NO_x molecules per joule and 4.6×10¹⁶ NO molecules per joule. An order of magnitude estimate of the NO and NO_x production per unit volume of heated gas based on a simple model show that the NO_x and NO production efficiency in air are about 3×10²² and 2×10²² molecules J⁻¹ m⁻³.     

Solid Substrate-Room Temperature Phosphorescence Method for the Determination of Trace Mn(II) Based on Oxidizing Reaction of Hydrogen Peroxide Using α,α′-Bipyridine as Sensitizer

A new solid substrate-room temperature phosphorescence (SS-RTP) method for the determination of trace manganese (II) has been established. It bases on the fact that fullerol (R) emits strong and stable room temperature phosphorescence (RTP) on filter paper substrate. H₂O₂ can oxidize R to cause the SS-RTP quenching. But manganese (II) can obstruct H₂O₂ to oxidize R, and enhance the RTP of R. α,α′-Bipyridine (Bipy) can sensitize the RTP. After adding Bipy, the ΔI _p enhances 7 times than that without Bipy. Under the optimum conditions, the linear dynamic range of this method is 0.016–1.12 pg spot⁻¹ with a detection limit (L.D.) of 4.6 fg spot⁻¹ ( is the absolute mass of Mn²⁺), and the regression equation of working curve is ΔI _p=25.20 + 63.55 (pg spot⁻¹), n=6, r=0.9983. For 0.016 and 1.12 pg spot⁻¹ Mn²⁺, RSDS are 4.3 and 4.8%, respectively (n=7). This method has been applied to the determination of trace manganese (II) in actual sample with high sensitivity and good selection. And the reaction mechanism of SS-RTP is discussed.     

Simulation on soot deposition and combustion in diesel particulate filter

We have simulated the flow in a real cordierite DPF using the lattice Boltzmann method. Inner structure of the filter is analyzed by a 3D X-ray CT technique. Two processes of soot deposition for PM trap and soot combustion for filter regeneration process are considered. Especially, the effect of NO₂ on the soot oxidation is examined, which is recently proposed as on-board regeneration system. The reaction rate has been determined based on previous experimental data. The estimated values of Arrhenius factor and activation energy are A = 146 1/s, E = 79.5 kJ/mol with NO₂, and A = 1.20 1/s, E = 64.9 kJ/mol without NO₂. Results show that, the flow field and pressure change inside the filter are clearly visualized. The pressure distribution depends on the non-uniformity of pore structure. The flow is largely changed with soot deposition, with higher pressure drop across the filter (filter back-pressure). The obtained correlation between total accumulated soot and the filter back-pressure is well in accordance with reported experimental results. In combustion simulation, the effect of NO₂ addition to promote the soot oxidation is confirmed. These are useful information to develop the future regenerating DPF system.     

A study of NOX production in air heated by laser discharges: Effect of energy, wavelength, multiple discharges and pressure

An experimental study on the production of NO_X in air heated under the action of a concentrated laser beam is presented. In this experiment laser induced plasma was produced in air in a closed Teflon chamber of inner volume 1600 cm³ by focusing a laser beam with either the wavelength of 1064 or 532 nm from a Q-switched Nd:YAG laser. The NO_X production was measured by chemiluminescence method and the possible effect of wavelengths, multiple discharges, and pressure on the yield of NO_X was studied. The results show that within the studied plasma energy range of 26–253 mJ for 532 nm beam and 16–610 mJ for 1064 nm beam, the NO_X production scales linearly with the dissipated plasma energy. For a given energy, 532 nm beam produces more NO_X in air at atmospheric pressure than the 1064 nm beam. In an attempt to see the possible influence of multiple discharges on the production of NO_X, discharges were created using 2–8 pulses with a repetition rate of 10 pulses per second in stationary air at atmospheric pressure. The results indicate that a certain amount of the NO_X created by a given pulse is destroyed by the subsequent pulses. In order to study the pressure dependence of the NO_X production, the pressure was varied from 16 to 100 kPa in the chamber and it was found that the NO_X production efficiency scales linearly with pressure.     

Metal/electrolyte surface chemistry: The adsorption of nitric acid and water on Ag(110)

The adsorption of HNO₃/H₂O mixtures on Ag(110) was investigated to learn more about the chemistry of the metal/electrolyte interface. The experiments were performed in ultrahigh vacuum (UHV) using thermal desorption spectroscopy (TDS), low energy electron diffraction (LEED), and electron stimulated desorption ion angular distribution (ESDIAD) over temperatures of 80–650 K and coverages of 0–10 monolayers (ML). As this is the first known study of HNO₃ in UHV, the mass spectrometer cracking pattern for HNO₃ is here reported. HNO₃ adsorbs irreversibly on the clean surface at 80 K and loses its acidic proton to form an adsorbed surface nitrate (NO₃) below 150 K. The saturation amount of adsorbed NO₃ is 0.4 ± 0.1 ML for which adsorption occurs in either a normal or split c(2 × 2) structure. N03 is stable on the surface up to 450 K beyond which it decomposes directly to gaseous NO₂ and NO and adsorbed atomic oxygen. NO₃ decomposition is first order with an activation energy E_a = 151±4 kJ mol⁻¹ and a pre-exponential factor of A = 10^15.4±0.4s⁻¹. NO₃ stabilizes adsorbed H₂O by about 8 kJ mol⁻¹ and is hydrated by as many as three H₂O molecules. Multilayers of HNO₃/H₂O desorb at 150–220 K and show evidence of extensive hydrogen bonding and hydration interactions. No evidence for HNO₃-induced corrosion or other surface damage was detected in any of these experiments.     

Flame structure of composite pseudo-propellants based on nitramines and azide polymers at high pressure

The chemical and thermal structures of flame of composite pseudo-propellants based on cyclic nitramines (HMX, RDX) and azide polymers (GAP and BAMO–AMMO copolymer) were investigated at a pressure of 1.0 MPa by molecular beam mass spectrometry and a microthermocouple technique. Eleven species H₂, H₂O, HCN, CO, CO₂, N₂, N₂O, CH₂O, NO, NO₂, and nitramine vapor (RDX_v or HMX_v), were identified, and their concentration profiles were measured in HMX/GAP and RDX/GAP pseudo-propellant flames at a pressure of 1 MPa. Two main zones of chemical reactions in the flame of nitramine/GAP pseudo-propellants were found. In the first, narrow, zone 0.1 mm wide (adjacent to the burning surface), complete consumption of nitramine vapor and NO₂ with the formation of NO, HCN, CO, H₂, and N₂ occurs. In the second, wider high-temperature zone, oxidation of HCN and CH₂O by NO and N₂O with the subsequent formation of CO, H₂, and N₂ takes place. The leading reactions in the high-temperature zone of flame of nitramine/GAP pseudo-propellants are the same as in the case of pure nitramines. In the case of nitramine/BAMO–AMMO pseudo-propellants a presence of carbonaceous particles on the burning surface did not allow us to analyze the zone adjacent to the burning surface, therefore only one flame zone was found. Temperature profiles in the combustion wave of nitramine/azide polymer pseudo-propellants were measured at 1 MPa. The data obtained can be used to develop and validate a self-sustain combustion model for pseudo-propellants based on nitramines and azide polymers.     

NO2 sensing properties of YSZ-based sensor using NiO and Cr-doped NiO sensing electrodes at high temperature

Nickel oxide and chromium-doped nickel oxide (Ni_0.95Cr_0.03O_1−δ ) were prepared by thermal decomposition of nitrates. The obtained NiO and Ni_0.95Cr_0.03O_1−δ samples were utilized as sensing electrodes (SEs) in yttria-stabilized zirconia (YSZ)-based sensors for detection of NO₂ at 800 °C under wet condition (5 vol.% H₂O). While the mixed-potential-type planar sensor attached with NiO-SE gave rather large NO₂ sensitivity, the sensor attached with Ni_0.95Cr_0.03O_1−δ -SE exhibited fast recovery rate with an acceptable sensitivity. The Δemf (electromotive force) of the sensors varied linearly with NO₂ concentration in the examined range of 50–400 ppm on a logarithmic scale. Based on the results of measurements for polarization, complex impedance and gas phase catalysis, the fast recovery was attributable to the high rate for the anodic reaction of O₂ at the Ni_0.95Cr_0.03O_1−δ /YSZ interface, and the lower NO₂ sensitivity was caused by both the high rate for the anodic reaction of O₂ and the high degree for the gas phase conversion of NO₂ to NO.     

Effect of intervening structure between CuO2 sheets in heavily Fe-substituted high-Tc superconductor FeSr2YCu2O6+δ

Heavily Fe-substituted Ba₂YCu₃O_6+δ-type compound FeSr₂YCu₂O_6+δ exhibits superconductivity around 60 K, only when it is annealed in N₂ and subsequently in O₂. Cationic distribution in this compound is strongly dependent on ionic radius at the Y site, and its superconducting properties are affected by the cationic distribution. In contrast, although the compound with the substitution of fluorite-type unit for Y has cationic order, it does not exhibit superconductivity. We have analyzed the crystal structure of the compounds with the substitution of other lanthanoid elements for Y and with substitution of fluorite-type unit for Y.     

Temperature dependence of the electrical resistivity of R6(Fe1-xMnx)23 compounds in the temperature range 4.2 to 300 K

The temperature dependence of the electrical resistivity of binary R₆Mn₂₃, R₆Fe₂₃ (R = Y, Dy, Ho, Er, Tm) and pseudobinary R₆(Fe_1-xMn_x)₂₃ (R = Y, Er, Ho) compounds has been determined by a four-probe measuring technique in the temperature range 4 to 400 K.The binary compounds exhibit a prop. T² dependence at low temperatures, while above 100 K a negative curvature of the -T-curves is observed.These experimental results are discussed on the basis of electron-spin wave scattering in the low temperature range and on the basis of s-d scattering in the high temperature range, taking explicitly into account the temperature dependence of the chemical potential.The pseudobinary compounds generally exhibit a decreasing resitivity with increasing temperature, combined with a high residual resistivity. These facts are explained by the so-called strong scattering mechanism and the appearance of “quasilocalized” states.     

Laser-induced reactions of NO2 in the visible region

The 488 nm laser-induced reaction of NO₂ with CO has been investigated and the results computer-modeled. Two reaction mechanisms were considered:1) the direct reaction of vibronically excited NO₂ (NO ₂ ^* ) with CO to form CO₂, and 2), the reaction of an intermediate NO₃ radical formed by the reaction of NO ₂ ^* with NO₂ followed by NO₃+CONO₂+CO₂. The modeling results strongly support the former as the dominant mechanism.Federal Junior Fellow (1980–1984)     

Unravelling combustion mechanisms through a quantitative understanding of elementary reactions

This review of the role of reaction kinetics in combustion chemistry traces the historical evolution and present state of qualitative and quantitative understanding of a number of reaction systems. Starting from the H₂–O₂ system, in particular from the reaction between H and O₂, mechanisms and key reactions for soot formation, for the appearance of NO_x, and for processes of peroxy radicals in hydrocarbon oxidation are illustrated. The struggle for precise rate constants on the experimental and theoretical side is demonstrated for the example of the reaction H + O₂ → OH + O. The intrinsic complexity of complex-forming bimolecular reactions, such as observed even in this reaction, also dominates most other key reactions of the systems considered and can be unravelled only with the help of quantum-chemical methods. The multi-channel character of these reactions often also requires the combination with master equation codes. Although kinetics provides an already impressive database for quantitative modelling of simple combustion systems, considerable effort is still required to quantitatively account for the complexities of more complicated fuel oxidation processes.     

Enols of 2‐nitro‐ and related 2‐substituted malonamides

The structures of 2‐substituted malonamides, YCH(CONR¹R²)CONR³R⁴ (Y = Br, SO₂Me, CONH₂, COMe, and NO₂) were investigated. When Y = Br, R¹R² = R³R⁴ = HEt; Y = SO₂Me, R¹–R⁴ = H and for Y = CONH₂ or CONHPh, R¹–R⁴ = Me, the structure in solution is that of the amide tautomer. X‐ray crystallography shows solid‐state amide structures for Y = SO₂Me or CONH₂, R¹–R⁴ = H. Nitromalonamide displays an enol structure in the solid state with a strong hydrogen bond (O^…O distance = 2.3730 Å at 100 K) and d(OH) ≠ d(O^…H). An apparently symmetric enol was observed in solution, even in appreciable percentages in highly polar solvents such as DMSO‐d₆, but K_enol values decrease on increasing the solvent polarity. The N,N′‐dimethyl derivative is less enolic. Acetylmalonamides display a mixture of enol on the acetyl group and amide in non‐polar solvents, and only the amide in DMSO‐d₆. DFT calculations gave the following order of pK_enol values for Y: H > CONH₂ > COMe ≥ COMe (on acetyl) ≥ MeSO₂ > CN > NO₂ in the gas phase, CHCl₃, and DMSO. The enol on the C?O group is preferred to the aci‐nitro compound, and the N? O? H^…O?C is less favored than the C?O? H^…O?C hydrogen bond. Copyright © 2009 John Wiley & Sons, Ltd.     

Improvement of the superconducting properties of an infiltrated YBCO bulk superconductor by a BaCeO3 addition

Single grain YBa₂Cu₃O_7−x (Y123) bulk superconductors with Y₂BaCuO₅ (Y211) and various amounts of BaCeO₃ (5–45 wt.% by an increment of 10 wt.%) were fabricated by a seeded infiltration process. The addition of BaCeO₃ was found to be effective for a modification of the microstructure and an improvement of the superconducting properties. The refinement effect for Y211 particles within an entire superconducting YBa₂Cu₃O_7−x (Y123) matrix was achieved by BaCeO₃ additions. The critical current density (J_c) values were increased as the BaCeO₃ contents were increased (maximum J_c at 35 wt.% BaCeO₃ addition). The J_c improvement by BaCeO₃ additions might be due to the microstructure modifications associated with the finely distributed Y211 and BaCeO₃ particles. With the addition of BaCeO₃ the onset T_c values decreased slightly, indicating highly limited Ce substitution for Y site. It can be concluded that the BaCeO₃ addition has a beneficial effect on the morphology, the size and the distribution of the Y211 inclusions and the microstructure regarding pinning improvement.