Effect of oxygen on CN bands emitted from active nitrogen flames

O₂ and C₂H₂ are added to the reacting N₂ afterglow + C₂H₂ which emits intense CN bands. The resulting changes in the spectra are examined. The results are presented and explained on the basis of C + O₂ → CO + O and N + O₂ → NO + O.     

Spectroscopic measurements of excited particles in a N2 gas RF plasma-assisted carbon laser ablation

In this work, we investigated a carbon plasma plume produced by laser ablation of a graphite target in a nitrogen gas environment. The spatial distributions of C and N atoms were measured by time-resolved absorption spectroscopy. The spatial distributions of the relative densities of CN radicals, C₂, and C₃ molecules were measured using time-resolved emission spectroscopy. We determined that nitrogen gas produced an increase in carbon atom and molecule densities in the ablation plume. It was observed that the addition of RF plasma to the plume increased the CN radicals and C atom densities, and decreased the C₂ and C₃ molecule densities. The RF plasma changed the evolution of various fractional species of C, N, CN, C₂, and C₃ in the ablation plume. The chemical reactions with and without RF plasma were explained using the evolution and density of the fractional species of C, N, CN, C₂, and C₃in the plume. PACS 52.38.Mf; 42.62.Fi; 33.20.-t; 81.05.Uw     

Basicity of trifluoromethylsulfonylformamidines. DFT and FTIR study and NBO analysis

The effect of the electron–acceptor substituent CF₃SO₂ at the imine nitrogen atom on the basicity and the electron distribution in N,N‐alkylformamidines ( 1 , 2 , 3 , 4 , 5 ) was studied experimentally by the FTIR spectroscopy and theoretically at the DFT (B3LYP/6‐311+G(d,p)) level of theory, including the natural bond orbital (NBO) analysis. The calculated proton affinities of the imine nitrogen atom and the sulfonyl oxygen (PA_N′ and PA_O) depend on the atomic charges, the C?N′ and N′―S bond polarity and on the energy of interaction of the amine nitrogen and the oxygen lone pairs with antibonding π* and σ*‐orbitals. The basicity of the imine nitrogen atom is increased with the increase of the electron‐donating power of the substituent at the amine nitrogen atom due to stronger interaction n_N → π*_C?N′, but is decreased for the electron‐withdrawing groups MeSO₂ and CF₃SO₂ at the imine nitrogen atom in spite of the increase of this conjugation. Protonation of ( 1 , 2 , 3 , 4 , 5 ) in CH₂Cl₂ solution in the presence of CF₃SO₃H occurs at the imine nitrogen atom, while the formation of hydrogen bonds with 4‐fluorophenol takes place at the sulfonyl oxygen atom, whose basicity is lower than that of N,N′‐dimethylmethanesulfonamide but higher than of N,N′‐dimethyltrifluoromethanesulfonamide. Copyright © 2015 John Wiley & Sons, Ltd.     

使用发射光谱对感应耦合CF4/CH4等离子体中C2基团形成机理的研究

利用强度标定的发射光谱法，研究了感应耦合CF4₄/CH4₄等离 子体中空间基团的 相对密度随宏观条件（射频输入功率、气压和流量比）的变化情况. 研究表明：在所研究的 碳氟/碳氢混合气体放电等离子体中除了具有丰富的CF，CF2₂，CH，H和F等活 性基团外 ，还同时存在着C2₂基团，其相对密度随着放电功率的提高而增加；随着气压 的上升呈 现倒“U”型的变化. C2₂随流量比R（R=［CH4 _{关键词： 发射光谱 感应耦合等离子体 2}基团')" href="#">C2₂基团     

Time‐resolved resonance Raman and density functional theory study of the photochemistry of 4‐benzoylpyridine in acetonitrile and 2‐propanol

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the intermolecular hydrogen‐abstraction reaction of the triplet state of 4‐benzoylpyridine (4‐BPy) in 2‐propanol solvent is reported. The TR³ results reveal a rapid hydrogen abstraction (<10 ns) by the 4‐BPy triplet state (nπ*) with the 2‐propanol solvent, leading to formation of a 4‐BPy ketyl radical and an associated dimethyl ketyl radical partner from the solvent. The recombination of these two radical species occurs with a time constant about 200 ns to produce a para‐N‐LAT (light absorbing transient). The structure, major spectral features, and identification of the ketyl radical and the para‐N‐LAT coupling complex have been determined and confirmed by comparison of the TR³ results with results from density functional theory (DFT) calculations. A reaction pathway for the photolysis of 4‐BPy in 2‐propanol deduced from the TR³ results is also presented. The electron‐withdrawing effect of the heterocyclic nitrogen for 4‐BPy on the triplet state makes it have a significantly higher chemical reactivity for the hydrogen abstraction with 2‐propanol compared to the previously reported corresponding benzophenone triplet reaction under similar reaction conditions. In addition, the 4‐BPy ketyl radical reacts with the dimethyl ketyl radical to attach at the para‐N atom position of the pyridine ring to form a cross‐coupling product such as 2‐[4‐(hydroxy‐phenyl‐methylene)‐4h‐pyridin‐1‐yl]‐propan‐2‐ol instead of attacking at the para‐C atom position as was observed for the corresponding benzophenone reaction reported in an earlier study. Copyright © 2008 John Wiley & Sons, Ltd.     

A Report on H mode in Magnetic Pole Enhanced Inductively Coupled Nitrogen Plasmas

The properties of low pressure magnetic pole enhanced, inductively coupled nitrogen plasma were studied by using electrical probe (Langmuir probe) under the conditions of RF powers in the range of 50‐220 W and pressures of 15‐75 mTorr. The electron energy probability function (EEPF) and electron density (n_e) obtained from the RF compensated Langmuir probe was compared with the theoretical results. The theoretical fits of the EEPF shows that the shapes of EEPF are evolved from generalised distribution to Maxwellian distribution function. It was also observed that at a low power (50 W) the discharge remains in inductive (H‐mode) mode for all the pressures (15‐75 mTorr). At a higher pressure and relatively low RF power, the measured EEPF show a hole near 3eV of energy. The intensities of the emission lines at 337.1nm (Second Positive System) and 391.4 nm (First Negative System) due to C³Π_u → B³Π_g and B²$\textstyle \sum_u^+$ → X² $\textstyle \sum_g^+$ transitions respectively, closely follows the variation of n_e with RF power and filling gas pressure. The stability of the H mode was also investigated using skin depth. Electron temperature and plasma potential indicate that the discharge at higher power (above 50 W) almost remain in H mode. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

P-violating effects in the polarization phenomena of the γ + D → N + P reaction near the threshold

Since at the threshold the P-odd amplitude of deuteron photodisintegration (γ + D → P + N) is determined by three independent multipole amplitudes (describing the El →¹S₀, El →³S₁, and M2 →³S₁ transitions), at least three different experiments on measuring the P-odd polarization characteristics of the γ + D → P + N process are needed (provided that P-odd threshold amplitudes are known) in order to determine the multipole amplitudes. A P-odd dependence of the threshold cross section on the polarizations of the colliding γ-quantum and deuteron is established and P-odd contributions to the polarization vector of protons formed in the γ + D → P + N process are found. The P-odd characteristics are calculated in terms of P-even and P-odd threshold amplitudes.     

Pulsed laser ablation of SiC in a nitrogen atmosphere: formation of CN

Optical emission lines from the plasma generated by a laser ablation process have been investigated to gather information on the nature of the chemical species present. In particular, the experiments were carried out during the laser ablation of a ceramic sintered SiC target, both in vacuum and in presence of controlled nitrogen atmosphere. Time integrated and spatially resolved emission spectra are dominated by the atomic emission lines from silicon and carbon species, either neutral, or singly ionized. When the ablation process was carried out in a nitrogen gas background direct evidence of the formation of the CN molecular specie was found. Fast photography imaging of the expanding plume revealed the formation of a shock wave at nitrogen pressure above 13.3 Pa, with the consequent heating of the shocked region and enhancement of the kinetics of ionization and excitation. Since the C₂ specie was absent, a CN formation mechanism involving atomic carbon and nitrogen in the presence of a shock wave is suggested. PACS 52.38.Mf; 52.50.Jm, 47.40.-x     

Time‐resolved Raman studies on Al2O3: Cr3+: lifetime measurements of the excited‐state transition Ē → 2Ā

A time‐resolved intensified charge coupled device‐based Raman microspectrometer system dedicated to the study of solid samples is described, offering good optical, temporal and spatial resolution. The advantages of this approach are demonstrated on Al₂O₃:Cr³⁺, obtaining for the first time the temporal evolution of the excited state transition Ē → 2Ā. Moreover, the time dependence of the luminescence due to the chromium ion was also determined by the same Raman device. Copyright © 2010 John Wiley & Sons, Ltd.     

He/Ar/Kr/F2混合气体中准分子KrF*和Kr2F*的动力学研究

本文用时间积分谱的方法研究了快放电激励下He/Ar/Kr/F₂混合气体中Kr₂F^*的动力学,探讨了Kr₂F^*形成的通道特性,理论分析和实验结果表明,在快放电激励下,三体碰撞过程KrF^*+Kr+M→Kr₂F^*+M是形成Kr₂F^*的主要通道,而置换反应ArF^*+Kr→KrF^*+Ar又能有效地产生KrF^*。实验测量了Kr₂F^*形成的有关速率常数。 关键词：     

大面积氮气均匀介质阻挡放电发射光谱研究

采用板-板式电极结构在大气压氮气中成功地获得了具有工业应用前景的大面积均匀介质阻挡放电等离子体。利用发射光谱技术测量了N₂(C3Π_u→B3Π_g)和N₂+(B2Σ+_u→X2Σ+_g 0-0 391.4 nm)的发射光谱,并研究了应用电压和驱动频率对N₂(C3Π_u→B3Π_g)和N₂+(B2Σ+_u→X2Σ+_g 0-0 391.4 nm)发射光谱强度的影响。结果表明,当应用电压小于6 kV时,N₂(C3Π_u→B3Π_g)和N₂+(B2Σ+_u→X2Σ+ _g0-0 391.4 nm)的发射光谱强度随应用电压增大变化较小,进一步升高应用电压时,等离子体发射光谱强度陡然增强。本文还讨论了激发态N+₂(B2Σ+_u)离子在纯N₂和He+N₂混合气体中介质阻挡大气压均匀介质阻挡放电下的主要产生机制。     

PECVD of Carbon Nanostructures in Hydrocarbon‐Based RF Plasmas

Different aspects of the plasma‐enhanced chemical vapor deposition of various carbon nanostructures in the ionized gas phase of high‐density, low‐temperature reactive plasmas of Ar+H₂+CH₄ gas mixtures are studied. The growth techniques, surface morphologies, densities and fluxes of major reactive species in the discharge, and effects of the transport of the plasma‐grown nanoparticles through the near‐substrate plasma sheath are examined. Possible growth precursors of the carbon nanostructures are also discussed. In particular, the experimental and numerical results indicate that it is likely that the aligned carbon nanotip structures are predominantly grown by the molecular and radical units, whereas the plasma‐grown nanoparticles are crucial components of polymorphous carbon films. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Is the neutral Knoevenagel reaction initiated by the carbanion formation?

The title reactions were studied by means of the density functional theory calculations. A base promoted reaction (called here ‘B’) was traced in a model composed of benzaldehyde, malononitrile, and (H₂O)₁₁. A neutral model (‘N’) of Ph‐CHO, H₂C(CN)₂ and (H₂O)₁₂ was also examined in line with a reported clean reaction. It was found that the ion pair of HC(CN) and H₃O⁺ is generated at the first step for N. For B, there are five elementary processes, and for N, four ones were obtained. By RB3LY/6‐311 + G** SCRF = PCM//RB3LYP/6‐31(+)G* energy calculations, the rate determining steps for both B and N reactions are the second proton removal, TS5(B) and TS3(N), respectively. In both B and N, the neutral species Ph(HO)HC‐CH(CN)₂ is the key intermediate. Copyright © 2010 John Wiley & Sons, Ltd.     

A DFT study of reduction of nitrobenzene to aniline with SnCl2 and hydrochloric acid

A fundamental reduction reaction, nitrobenzene to aniline in SnCl₂ and hydrochloric acid, was investigated by density functional theory (DFT) calculations. First, the change of SnCl₂ → SnCl₄^2? → Cl₄SnH^? was discussed, and the reaction path of SnCl₄^2? + H₃O⁺ → Cl₄SnH^? + H₂O was obtained. Starting from nitrobenzene, six elementary processes were found so as to arrive at the protonated aniline. The hydride ion from Cl₄SnH^? is connected always to the cationic nitrogen, and the proton is always to oxygens. An intermediate Ph?N⁺H₂OH was obtained, which is isomerized to the para O?H adduct protonated imine via the Bamberger rearrangement. This species may undergo the H^? acceptance at the sp² N⁺H₂ center. In the nitrobenzene reduction, the proton enhances the electrophilicity of the nitrogen center, which makes the hydride shift ready. N?H bonds are formed, and N?O bonds are cleaved both by the proton attach and subsequent H₂O elimination and by the formal [1,5] OH shift. Copyright © 2016 John Wiley & Sons, Ltd.     

Optical characterization of atmospheric‐pressure plasma needle

The atmospheric‐pressure plasma needle is a promising source that can be used efficiently for different industrial applications. A radio frequency (RF) (13.56 MHz) generator was used to generate a He–O₂/Ar mixture plasma. The ground‐state oxygen atomic density [O] was calculated as a function of discharge parameters by “actinometry”. The Ar‐I (2p₁ → 1s₂) line at 750 nm and the O‐I (³P → ³S) line at 844 nm were used to estimate the [O] atomic density. The rotational temperature T _R of He–O₂/Ar mixture was measured from the rotational levels of the “first negative system” (FNS) by using the “Boltzmann plot”. The effect of discharge parameters on the atomic oxygen density [O] and the gas temperature was monitored. These results show that [O] density increases with RF power and O₂ concentration, but decreases with the gas flow rate. Whereas the gas temperature increases with increase in the input RF power, it decreases with increase in the gas flow rate and O₂ concentration in the mixture. Since the [O] atomic density contributes to plasma‐based biomedical applications, the proposed optimum conditions for plasma‐based decontamination of heat‐sensitive materials in the present study are 0.6% oxygen, 500 sccm flow rate, and 26 W RF power.     

Sequence of phase formation during solid-state synthesis in Al/Ni films (Al: Ni = 60: 40 at %)

The structure formed during solid-state synthesis in thin bilayer Al/Ni films with the ratio Al: Ni = 60: 40 (at %) has been investigated. The films were obtained by thermal evaporation in vacuum with a residual pressure of 10^?5–10^?6 Torr. Solid-state synthesis was performed by diffusion reaction. The sequence of phase formation upon vacuum annealing of bilayer Al/Ni films has been established: Al + Ni → Al₃Ni + Ni (T _ann = 180°C) → Al₃Ni₂ (T _ann = 220°C).     

Effect of ambient nitrogen pressure on the formation and spatio-temporal behaviour of C<Subscript>2</Subscript> and CN

We report the effect of ambient gas on the formation as well as propagation behaviour of ablated species C₂ and CN within the carbon plasma created by focussing a high-power Nd:YAG (λ = 1064 nm) laser onto the rotating graphite target in the nitrogen ambient. The formation of C₂ takes place earlier as well as nearer the target compared to that of CN which forms later and far from the target, in 1.2 mbar pressure of N₂ gas. Peak arrival time vs. nitrogen gas pressure plot shows a shock wave-like dependence t ∝ p ⁿ in the pressure range 1.2–120 mbar (collisional regime) which indicates plume confinement with increases in ambient pressure. At higher pressure, thermalization takes place.     

Carbon nitride films by RF plasma assisted PLD: Spectroscopic and electronic analysis

Carbon nitride (CNx) thin films have been grown on Si 〈1 0 0〉 by 193 nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N₂ plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C⁺ ions, C atoms, C₂, N₂; and CN radicals, and N₂⁺ molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the “four-probe-test method” determining sheet resistivity and correlating surface conductivity with chemical composition.     

Modelling the effects of nitrogen doping on the carbon nanofiber growth via catalytic plasma‐enhanced chemical vapour deposition process

An analytical model is developed to describe the effects of nitrogen doping on the growth of the carbon nanofibers (CNFs) and to elucidate the growth mechanism of nitrogen‐contained carbon nanofibers (N‐CNFs) on the catalyst substrate surface through the plasma‐enhanced chemical vapour deposition (PECVD) process. The analytical model accounts for the charging of CNFs, kinetics of all plasma species (electrons, ions, and neutrals) in the reactive plasma, generation of carbon species on the catalyst nanoparticle surface due to dissociation of hydrocarbons, CNF growth due to diffusion and precipitation of carbon species, and various other processes. First‐order differential equations have been solved for glow discharge plasma parameters for undoped CNFs (CNF growth in C₂H₂/H₂ plasma) and nitrogen‐doped CNFs (N‐CNF growth in C₂H₂/NH₃ plasma). Our investigation found that nitrogen‐doped CNFs exhibit lower tip diameters and smaller heights compared to the undoped CNFs. In addition, we have estimated that nitrogen‐doped CNFs have more enhanced field emission characteristics than the undoped CNFs. Moreover, we have also observed that N‐CNFs' growth rate increases and tip diameter decreases as the C₂H₂/NH₃ gas ratio decreases. The theoretical results of the present investigation are consistent with the existing experimental observations.     

Determination of the Energy Flux of a Commercial Atmospheric‐Pressure Plasma Jet for Different Process Gases and Distances Between Nozzle Outlet and Substrate Surface

The energy flux of an atmospheric‐pressure plasma jet for surface treatment has been investigated by a calorimetric probe. Generally, the investigations exhibit that the main contributions of the total energy influx from the plasma to the substrate surface originate from the neutrals regarding high gas temperature coupled with a high gas flow. The use of nitrogen as process gas shows a higher energy flux compared to oxygen and air presumably caused by increased gas temperature as well as by higher molecule formation and recombination energy of N₂. Moreover, the lateral expansion of the plasma beam could be roughly determined by a spatially resolved analysis of the energy influx. A top part mounted on the nozzle, commonly used for the injection of additional precursor gases, showed a significant effect on the flow behavior and collision entailed relaxation of the excited plasma species leading to a restraining of the plasma jet. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)