Densities of Active Species in R/x%(N2–5%H2) (R = Ar or He) Microwave Flowing Afterglows

Plasma Chemistry and Plasma Processing - Afterglows of R/x(N2–5%H2) (R?=?Ar or He) flowing microwave discharges are characterized by optical emission spectroscopy. Absolute...     

Correction to: Densities of Active Species in R/x%(N2–5%H2) (R = Ar or He) Microwave Flowing Afterglows

Plasma Chemistry and Plasma Processing - Unfortunately, the original publication contains errors. The authors would like to correct the errors as given.     

Experimental determination of the dissociation energies D0 and De of H2O…HF

The zero-point and equilibrium dissociation energies of the hydrogen-bonded dimer H₂O…HF have been determined as D₀ = 34.3(3) kJmol⁻¹ and D_e = 42.9 (8) kJmol⁻¹ from absolute intensities of rotational transitions in an equilibrium mixture of H₂O, HF and H₂O…HF.     

Study of correlation effects on stretching force constants of the H3N⋯LiF lithium-bonded and H3N⋯HF hydrogen-bonded complexes

All quadratic, cubic and quartic force constants associated with high and low vibrational modes of the H₃N⋯HF hydrogen-bonded and H₃N⋯LiF lithium-bonded complexes have been calculated employing the Møller—Plesset perturbation theory to the second order (MP2) with the 4-31G** basis set.     

DFT Study on the Os^＋-catalytic Reduction Reaction of N2O with H2 in the Gas Phase

The Os+-catalytic reduction of N2O by H2 in gas phase has been theoretically investigated with B3LYP method.The reaction mechanisms on the sextet and quartet surfaces were found to be similar.The calculated sextet potential energy profiles show that the two reactions involved in the catalytic cycle,Os+ + N2O → OsO+ + N2 and OsO+ + H2 → Os+ + H2O,have barriers of 28.3 and 123.3 kJ/mol,respectively.In contrast,the reactions on the quartet surfaces are energetically much more favorable.These results rationalize the experimentally observed low catalytic reactivity of sextet(ground-state) Os+.Further,the crossing between the sextet and quartet surfaces are also suggested and qualitatively discussed.     

TD-DFT Study on the Excited-State Hydrogen Bonding of the p-Cresol–NH3–H2O Complex

In this work, the time-dependent density functional theory (TD-DFT) method was used to study the electronic excited-state dynamics of the hydrogen-bonded p-Cresol–NH₃–H₂O complex. The intermolecular hydrogen bonds O₁–H₁···N and C–O₁···H₂ were demonstrated by the optimized geometric structure of the hydrogen-bonded p-Cresol–NH₃–H₂O complex. The infrared spectra (IR spectra) of the hydrogen-bonded p-Cresol–NH₃–H₂O complex in the ground and excited states were also calculated by using the density functional theory (DFT) and TD-DFT methods. It is demonstrated that hydrogen bond O₁–H₁···N can be strengthened while hydrogen bond C–O₁···H₂ is weakened upon photoexcitation to the S₁ state. The significant changes of the hydrogen bond from the calculated bond lengths in different electronic states can be observed. In addition, the spectral shifts of the stretching vibrational mode of the hydrogen-bonded O–H group in different electronic states are accounted for the hydrogen bond changes in the S₁ state too.     

Generator of an H2Se–H2 Mixture,Based on Packing with Selenium Reflux. Part 1. Development of the Design and Experimental Study of the Generator

Russian Journal of Applied Chemistry - Generators of an H2Se–H2 mixture, based on a packing with liquid selenium reflux and addition of selenium from an external source, are considered....     

A Theoretical Study on Nonadiabatic Trapping Models of the Reaction NH H←→N H_2

ThehydrogenatomtransferreactionNH H-N H,isanimportantreactioninradicalreactionsandthegas-phrasethermatdecompositionofammonia.Therewereseveralstudiesonthisreactioninexperiment]andtheory='3.Inthispaper,wehaveemployedtheunifiedstatisticaltheory'(UST)tos...     

Theoretical Study on the Mechanism of VO2^＋ ＋ H2 Reaction in the Gas Phase

The mechanism of VO2+ + H2 reaction in the gas phase was investigated by using density functional theory (DFT) at the CCSD//B3LYP/6-311G(2d, p) level. According to our calculation results, the different reaction mechanisms were found for the singlet and triplet potential energy surfaces (PESs). Especially, the crossing points (CPs) among different PESs were located by means of the intrinsic reaction coordinate (IRC) approach presented by Yoshizawa et al., and the structures and energies of the corresponding minimum energy crossing points (MECPs) were obtained by the mathematical algorithm proposed by Harvey et al. Finally, the frontier molecular orbital (FMO) interaction analyses about MECP1 and MECP2 were used to prove our calculation results.     

Study on the Effect of Nano and Active Particles of Alumina on Natural Rubber–Alumina Composites in the Presence of Epoxidized Natural Rubber as Compatibilizer

Natural rubber composites with alumina of different particle sizes (28 nm nano particles, 200 nm active particles and > 1000 nm raw alumina) were prepared by the usual rubber processing technique. Epoxidized natural rubber (ENR) was used in the composites as compatibilizer. Cure characteristics and mechanical properties of all composites were analyzed. The values of minimum rheometric torque (M_L), maximum rheometric torque (M_H) and torque difference (M_H – M_L) increased. Maximum enhancement was observed for the nano-filled composites. It endorses the view that nano alumina reveals highest interaction with natural rubber in presence of ENR. Scorch time and optimum cure time values for nano-composites were highest among all types of composites. Vulcanization reaction for the sulfur curing system of the composites was found to follow first order rate kinetics. Specific rate constant decreased with decreasing particle size in composites. Crosslink densities of composite-vulcanizates showed increasing trend with decreasing particle size of alumina. Mechanical properties of the composite vulcanizates increased with decreasing particle size of alumina - nano composites exhibiting much higher mechanical strength. Results of oxidative resistance reveal that particle size of alumina in composite vulcanizates has a significant impact on aging behavior.     

Comparison of the Active Species in the RF and Microwave Flowing Discharges of N<Subscript>2</Subscript> and Ar–20 %N<Subscript>2</Subscript>

We report a detailed comparison between RF and microwave (HF) plasmas of N₂ and Ar–20 %N₂ as well as in the corresponding afterglows by comparing densities of active species at nearly the same discharge conditions of tube diameter (5–6 mm), gas pressure (6–8 Torr), flow rate (0.6–1.0 slm) and applied power (50–150 W). The analysis reveals an interesting difference between the two cases; the length of the RF plasma (~25 cm) is measured to be much longer than that of HF (6 cm). This ensures a much longer residence time (10^?2 s) of the active species in the N₂ RF plasma [compared to that (10^?3 s) of HF], providing a condition for an efficient vibrational excitation of N₂(X, v) by (V–V) climbing-up processes, making the RF plasma more vibrationally excited than the HF one. As a result of high V–V plasma excitation in RF, the densities of the vibrationally excited N₂(X, v > 13) molecules are higher in the RF afterglow than in the HF afterglow. Destruction of N₂(X, v) due to the tube wall is estimated to be very similar between the two system as can be inferred from the γ_v destruction probability of N₂(X, v > 3–13) on the tube wall (2–3 × 10^?3 for both cases) obtained from a comparison between the density of N₂(X, v > 3–9) in the plasmas to that of the N₂(X, v > 13) in the long afterglows. Interestingly enough, densities of N-atoms and N₂(A) metastable molecules in the afterglow regions, however, are measured to be very similar with each other. The measured lower density of N₂ ⁺ ions than expected in the HF afterglow is rationalized from a high oxygen impurity in our HF setup since N₂ ⁺ ions are very sensitive to oxygen impurity .     

X-ray Diffraction Study of Phases in the System CaS-Lu2S3 (0–50 mol % Lu2S3)

Thirteen samples were synthesized in the system CaS-Lu₂S₃ in the range 0-50 mol % Lu₂S₃ and studied by X-ray powder diffraction (phase analysis, determination and refinement of unit cell parameters, Rietveld structure refinement). The phases crystallizing in the system have NaCl-type structures (space group Fm3m, unit cell parameter a ₀) with a cubic, hexagonal, or orthorhombic superstructure, the respective structure types being Yb_0.875S (space group F4?3m, a~ 2a ₀), CaY₂Se₄ (space group $R?erline 3m, {∈xt a ¡m {a_0}sqrt 2}, {∈xt c ¡m 2{a_0}sqrt 3}$), and Tm_0.76Se (space group Pnnn; $a ¡m {a_0}sqrt 2, {∈xt b ¡m {a_0}sqrt 2}, {∈xt c ¡m 2{a_0}}$), and a phase with a Yb₃S₄-type orthorhombic unit cell (space group Pnma).     

Experimental and theoretical study of the dissociation enthalpy of the N–O bond on 2-hydroxypyridine N-oxide: theoretical analysis of the energetics of the N–O bond for hydroxypyrydine N-oxide isomers

The standard (p^∘=0.1 MPa) molar enthalpy of formation of crystalline 2-hydroxypyridine N-oxide was measured, at T=298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T=298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation of 2-hydroxypyridine N-oxide in gaseous phase, and to evaluate the dissociation enthalpy of the N–O bond. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for the three isomers of hydroxypyridine N-oxide in order to confirm the experimental trend for the dissociation enthalpy of the (N–O) bond.     

The rotational spectrum of the hydrogen-bonded heterodimer H2O…HF in the frequency range 40–80 GHz

The μ_a R-branch rotational spectra of the ground and first excited states of the three lowest vibrational modes of the H₂O…HF heterodimer have been observed in the frequency range 40–80 GHz. Coriolis perturbations between the ground vibrational state (υ = 0) and the first excited state of the out-of-plane bending vibration (υ_β(0) = 1) show that for a given J the K₋₁ = 2 levels of υ_β(0) = 1 lie approximately 3 cm⁻¹ above the K₋₁ = 3 levels of υ = 0. The vibrational separation between these two states is estimated to be 70±3 cm⁻¹. This value is consistent with those determined by other methods and reinforces the conclusion that ν_β(0) is governed by a double-minimum potential energy function with the quantitative form previously published. A perturbation is also observed in the first excited state of the hydrogen-bond stretching vibration υ_σ = 1. This manifests itself as a large, negative centrifugal distortion constant D_JK = −8.5 MHz compared with 2 MHz in the other vibrational states.     

Influence of SrO content on microstructure and crystallization of glazes in the SiO2–Al2O3–CaO–MgO–K2O system

The effect of the SrO addition on the microstructure and structure of the glazes from the SiO₂–Al₂O₃–CaO–MgO–K₂O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range.

     

Numerical simulations on effects of oxygen concentration on the structure and soot formation in a two-dimensional axisymmetric laminar C2H4/(O2–CO2) diffusion flame

Journal of Thermal Analysis and Calorimetry - In this paper, based on the oxy-fuel and dry product cycle combustion as an application background, using the CoFlame laminar flame procedures, we...     

Comparative Study of the Efficiency of New Technical Carbons СН210 and С40 in Electrosynthesis of Н2О2 from О2 in Gas-Diffusion Electrodes on Their Basis

Russian Journal of Electrochemistry - The efficiency of new brands of technical carbon CH210 and C40 in the electrogeneration of Н2О2 from О2 in gas-diffusion electrodes (GDE) on...     

Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

Formation of Diazepam–Lanthanides(III) Complexes in the 50–50 Volume % Ethanol–Water Solvent System and Study of the Effect of Temperature on the Complex Formation Constants

Diazepam (7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one) is an important derivative of the 1,4-benzodiazepine compound commercially distributed as Valium. The complex formation constants of diazepam with some light lanthanide(III) metal ions have been studied by potentiometric measurements. All titrations were performed in 50–50% (volume/volume) ethanol–water solvent mixtures at constant ionic strength (0.10 mol⋅dm⁻³). The ionic strength was maintained by using sodium perchlorate. The complex formation constants were determined at 25.00, 35.00 and 45.00 °C. With increasing temperature, a decrease was observed in the protonation constant (pK) of diazepam.