Production of N,H, and NH active species in N2-H2 dc flowing discharges

Densities of N, H, and NH active species have been detected by laser-induced fluorescence (LIF) in N₂-xH₂ dc flowing discharges. A peak value of N atom densities far x = 0.2–0.5% and a plateau value of H atom densities between x = 1% and 90% in post-discharge conditions (0.05 sec, p = 2 torr) has been found. Comparison between LIF measurements of N atoms and the trend of the N₂(B, v = II) population shows that the emission from this state can be used for monitoring N atoms. The NH radical has only been detected inside the discharge region.On leave from Instituto Tecnológico de Aeronáutica, CNPq, Brazil.     

NH4VO3在NH4H2PO4-H2O和(NH4)3PO4-H2O体系中的溶解度

采用等温溶解法测定了偏钒酸铵(NH₄VO₃)在NH₄H₂PO₄-H₂O和(NH₄)₃PO₄-H₂O体系中T = 298.15-328.15 K时的溶解度以及溶液的密度和pH值。结果表明, NH₄VO₃的溶解度随着(NH₄)₃PO₄或NH₄H₂PO₄溶液浓度的增大,先降低后升高,这是由于同离子效应、化学反应平衡及离子活度的共同作用。比较T = 298.15K时, NH₄VO₃分别在NH₄H₂PO₄-H₂O、(NH₄)₂HPO₄-H₂O和(NH₄)₃PO₄-H₂O体系中溶解度,发现在相同的磷酸盐浓度下, NH₄VO₃的溶解度在NH₄H₂PO₄-H₂O体系中最大,在(NH₄)₃PO₄-H₂O体系中居中,在(NH₄)₂HPO₄-H₂O体系中最小。进一步地,在T = 298.15 K和磷酸盐浓度C = 0.5 mol·kg^-1时,结合pH值和反应溶度积常数K_SP等计算三个体系中的平均离子活度系数(γ_±),发现γ_±值在(NH₄)₂HPO₄-H₂O体系中最大,在(NH₄)₃PO₄-H₂O体系中居中,在NH₄H₂PO₄-H₂O体系中最小,与溶解度规律一致。     

Interest of NH3 and N2 plasmas for polymer surface treatment before “electroless” metallization

The electroless metallization of polymers needs an activation of their surface which consists of palladium chemisorption. In this study, the effect of surface treatments of polystyrene and polyamide substrates by reactive gas plasmas (O₂, NH₃, N₂) has been followed by XPS analysis. According to the functional groups grafted on the surface, specific chemisorption reactions can occur. The latter have been highlighted through a comparative investigation of two activation processes, viz. a conventional way using successively SnCl₂ and PdCl₂ solutions and a new procedure, developed by the authors, using only a PdCl₂ solution. This work shows that this simplified process can be extended to any polymer whose surface is grafted with nitrogenated functions.     

Neutral and ion chemistry in low pressure dc plasmas of H2/N2 mixtures: routes for the efficient production of NH3 and NH4(+)

The chemistry in low pressure (0.8-8 Pa) plasmas of H(2) + 10% N(2) mixtures has been experimentally investigated in a hollow cathode dc reactor using electrical probes for the estimation of electron temperatures and densities, and mass spectrometry to determine the concentration of ions and stable neutral species. The analysis of the measurements by means of a kinetic model has allowed the identification of the main physicochemical mechanisms responsible for the observed distributions of neutrals and ions and for their evolution with discharge pressure. The chemistry of neutral species is dominated by the formation of appreciable amounts of NH(3) at the metallic walls of the reactor through the successive hydrogenation of atomic nitrogen and nitrogen containing radicals. Both Eley-Rideal and Langmuir-Hinshelwood mechanisms are needed in the chain of hydrogenation steps in order to account satisfactorily for the observed ammonia concentrations, which, in the steady state, are found to reach values ~30-70% of those of N(2). The ionic composition of the plasma, which is entirely due to gas-phase processes, is the result of a competition between direct electron impact dissociation, more relevant for high electron temperatures (lower pressures), and ion-molecule chemistry that prevails for the lower electron temperatures (higher pressures). At the lowest pressure, products from the protonation of the precursor molecules (H(3)(+), N(2)H(+) and NH(4)(+)) and others from direct ionization (H(2)(+) and NH(3)(+)) are found in comparable amounts. At the higher pressures, the ionic distribution is largely dominated by ammonium. It is found that collisions of H(3)(+), NH(3)(+) and N(2)H(+) with the minor neutral component NH(3) are to a great extent responsible for the final prevalence of NH(4)(+).     

Photolysis of solid NH3 and NH3-H2O mixtures at 193 nm

We have studied UV photolysis of solid ammonia and ammonia-dihydrate samples at 40 K, using infrared spectroscopy, mass spectrometry, and microgravimetry. We have shown that in the pure NH(3) sample, the main species ejected are NH(3), H(2), and N(2), where the hydrogen and nitrogen increase with laser fluence. This increase in N(2) ejection with laser fluence explains the increase in mass loss rate detected by a microbalance. In contrast, for the ammonia-water mixture, we see very weak signals of H(2) and N(2) in the mass spectrometer, consistent with the very small mass loss during the experiment and with a <5% decrease in the NH(3) infrared absorption bands spectroscopy after a fluence of ~3 × 10(19) photons/cm(2). The results imply that ammonia-ice mixtures in the outer solar system are relatively stable under solar irradiation.     

高碘酸盐-硫脲-硫酸反应体系的非线性动力学

研究了KIO4 SC(NH2)2 H2SO4反应体系在封闭、半封闭以及开放系统中的非线性动力学行为.发现在封闭体系中体系的吸光度、铂电极电位和pH值呈现单峰或准振荡现象；在半封闭和开放系统中体系的铂电极电位和碘电极电位均呈振荡现象.封闭、半封闭及开放系统的动力学曲线受体系酸度和初始浓度比值[KIO4]0/[SC(NH2)2]0的影响.对照其在封闭、半封闭和开放系统中的动力学行为,以碘单质产生和消耗驱使的反应动力学可解释该反应体系的复杂现象.     

Computer simulation of interactions in the NH3-CO2-H2O system

Computer simulation of interactions in the NH₃-CO₂-H₂O system was performed using a quantum-chemical method B3LYP/6-31G(d,p) for the simulation of the possible routes of the reactions and the estimation of the energy parameters: interaction energy between molecules in complexes, activation energy of forward and reverse reactions, and the heat of the reaction. A new version of termolecular reaction mechanism is proposed and investigated. The probability of realization of various paths of interaction in the NH₃-CO₂-H₂O system was shown to be determined by the temperature: at low temperatures the termolecular mechanism is more probable, while at the temperatures close to the standard conditions carbamate and bimolecular mechanisms are preferable.     

Crystallization mechanism study on ZSM-48 in the system Na2O-Al2O3-SiO2-H2N(CH2)6NH2

The crystallization mechanism of ZSM-48 in the system Na₂O-Al₂O₃-SiO₂-H₂N(CH₂)₆NH₂ was studied by using XRD, SEM, TG/DTA, FTIR, XPS and plasma spectra techniques. It is shown that the reaction mixture is crystallized through solid—solid mass transformation. It was found, by tracing the crystallization process, that a secondary gel composed of silicate and aluminosilicate, in which SiO₄ and AlO₄ tetrahedra quickly form with some Al atoms, transferred to the surface, before generating nuclei. Possibly, a C-model (can and cement model) may be used to elucidate the evolution of nucleation. SEM showed that dendritic and entangled nuclei first form in the inner portion of the solid fraction. TG/DTA showed that the organic amine content in the solid sample increases with increasing crystallinity, which gives strong evidence for the organic amine being a template. FTIR revealed that the structure consisting of six-membered rings and double five-membered rings forms after about eight days through rearrangement and coalescence.     

The Mechanisms of Formation and Decay of Atoms in N2-H2 Plasmas

The formation rate and number densities of H(² S) and N(⁴ S) atoms, rate constants of their heterogeneous decay, and some electrophysical characteristics of plasma were measured in the positive column of a dc discharge in an H₂–N₂ gas mixture at a pressure of 266 Pa and a discharge current of 50 mA. From these data, by the combined solution of the Boltzmann equation, vibrational kinetics equations for ₂(X ¹_g) and N₂(X ¹_g), chemical kinetics equations, and plasma energy and heat balance equations, it was found that vibrationally excited nitrogen molecules must play a substantial role in the formation of both hydrogen and nitrogen atoms.     

Ion chemistry in cold plasmas of H2 with CH4 and N2

The distributions of ions and neutrals in low-pressure (approximately 10(-2) mbar) DC discharges of pure hydrogen and hydrogen with small admixtures (5%) of CH(4) and N(2) have been determined by mass spectrometry. Besides the mentioned plasma precursors, appreciable amounts of NH(3) and C(2)H(x) hydrocarbons, probably mostly from wall reactions, are detected in the gas phase. Primary ions, formed by electron impact in the glow region, undergo a series of charge transfer and reactive collisions that determine the ultimate ion distribution in the various plasmas. A comparison of the ion mass spectra for the different mixtures, taking into account the mass spectra of neutrals, provides interesting information on the key reactions among ions. The prevalent ion is H3+ in all cases, and the ion chemistry is dominated by protonation reactions of this ion and some of its derivatives. Besides the purely hydrogenic ions, N(2)H+, NH(4)+, and CH(5)+ are found in significant amounts. The only mixed C/N ion clearly identified is protonated acetonitrile C(2)H(4)N+. The results suggest that very little HCN is formed in the plasmas under study.     

Photogeneration of metastable side-on N2 linkage isomers in [Ru(NH3)5N2]Cl2, [Ru(NH3)5N2]Br2 and [Os(NH3)5N2]Cl2

Photogeneration of side-on N2 linkage isomers in [Ru(NH3)5N2]2+ and [Os(NH3)5N2]2+ is achieved by irradiation with lambda = 325 nm of powder samples at T = 80 K and detected by the downshift of the nu(N-N) vibration and by the heat release at elevated temperature due to the back switching of the side-on configuration to the ground state. The concentration of the transferred molecules is evaluated by the decrease of the area of the nu(N-N) or 2nu(N-N) vibrational bands. All characteristic changes between the linear Ru-N-N and side-on configuration are predicted by DFT calculations: the structure of the anion, shifts of the vibrations, electronic excitation energy, energetic position and sequence of the electronic orbitals, the potentials of the ground and relaxed metastable state with the activation energy, saddle points and energetic position of the minimum.     

高碘酸盐-硫脲-硫酸反应体系的非线性动力学

研究了KIO4-SC(NH2)2-H2SO4反应体系在封闭、半封闭以及开放系统中的非线性动力学行为.发现在封闭体系中体系的吸光度、铂电极电位和pH值呈现单峰或准振荡现象;在半封闭和开放系统中体系的铂电极电位和碘电极电位均呈振荡现象.封闭、半封闭及开放系统的动力学曲线受体系酸度和初始浓度比值犤KIO4犦0/犤SC(NH2)2犦0的影响.对照其在封闭、半封闭和开放系统中的动力学行为,以碘单质产生和消耗驱使的反应动力学可解释该反应体系的复杂现象.     

Synthesis and characterization of Th2N2(NH) isomorphous to Th2N3

Using a new, low-temperature, fluoride-based process, thorium nitride imide of the chemical formula Th(2)N(2)(NH) was synthesized from thorium dioxide via an ammonium thorium fluoride intermediate. The resulting product phase was characterized by powder X-ray diffraction (XRD) analysis and was found to be crystallographically similar to Th(2)N(3). Its unit cell was hexagonal with a space group of P3m1 and lattice parameters of a = b = 3.886(1) and c = 6.185(2) ?. The presence of -NH in the nitride phase was verified by Fourier transform infrared spectroscopy (FTIR). Total energy calculations performed using all-electron scalar relativistic density functional theory (DFT) showed that the hydrogen atom in the Th(2)N(2)(NH) prefers to bond with nitrogen atoms occupying 1a Wyckoff positions of the unit cell. Lattice fringe disruptions observed in nanoparticle areas of the nitride species by high-resolution transmission electron microscopic (HRTEM) images also displayed some evidence for the presence of -NH group. As ThO(2) was identified as an impurity, possible reaction mechanisms involving its formation are discussed.     

Wavelength and fluence dependences of the IR multiple photon dissociation of CH3NH2 to form ground state NH2 radicals

Ground state NH₂ radicals have been detected by laser excited fluorescence following the collisionless multiple photon dissociation of CH₃NH₂ by a pulsed CO₂ laser. The variation of dissociation yield with IR laser fluence and wavelength are reported for several CO₂ lines overlapping the CH₃NH₂ν₈ band. Dissociation is more efficient at wavelengths corresponding to initial absorption in the P branch of this transition than for excitation in the Q or R branches, with the difference in efficiencies being more pronounced at lower fluences. The mechanism of NH₂ production appears to be direct C-N bond fission.     

Chemical mechanisms in C3F8-H2 radiofrequency discharges

Discharges fed with C₃F₈-H₂ mixtures have been studied by means of mass spectrometry in a tubular reactor operated at 0.5 torr and 50 W. Comparison of the results with those obtained with emission actinometry give additional evidence that emission actinometry and mass spectrometry are powerful diagnostic tools to monitor stable and unstable species in discharges utilized for dry etching and polymer depositions. Mechanisms for end product formation and polymer deposition are also discussed.     

Das System Ca(N3)2-H2O

Zusammenfassung Das Zustandsdiagramm für das System Ca(N₃)₂-H₂O wird auf Grund von Gefrierpunkts- und Löslichkeitsmessungen auf-gestellt. Ferner werden Lösungswärmen bestimmt und Dampfdruckmessungen vorgenommen. Durch Aufstellen eines Kreisprozesses werden die Normalbildungsenthalpien folgender Verbindungen bestimmt: Ca(N₃)₂, Ca(N₃)₂·0,5 H₂O, Ca(N₃)₂·1,5 H₂O und Ca(N₃)₂·4 H₂O.

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The system Ca(N₃)₂-H₂O

Based on measurements of freezing points and solubility the phase diagram of the system Ca(N₃)₂-H₂O is given. Furthermore, investigations on the heat of solution and measurements of the vapor pressure were carried out. By setting up a cycle process the standard enthalpies of formation for the following compounds were determined: Ca(N₃)₂, Ca(N₃)₂·0,5 H₂O, Ca(N₃)₂·1,5 H₂O and Ca(N₃)₂·4 H₂O.

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