Electron behaviour in CH4／H2 gas mixture in electron-assisted chemical vapour deposition

The behaviour of electrons in CH_{4}/H_{2} gas mixture in electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron drift velocity in gas mixture is obtained over a wide range of E/P (the ratio of the electric field to gas pressure) from 1500 to 300000 (V/m kPa^{-1}). The electron energy distribution and average energy under different gas pressure (0.1－20kPa) and CH_{4} concentration (0.5%－10.0%) are calculated. Their effects on the diamond growth are also discussed. It is believed that these results will be helpful to the selection of optimum experimental conditions for high quality diamond film deposition.     

Der Einfluß der Eigenraumladung auf die Trägervermehrung einer Lawine in N2, CH4 und N2+CH4

In gases with highγ, e.g. N₂, in which the carrier amplification is max. 10⁴ at the static breakdown, electron avalanches with a carrier amplification up to 10⁹ are produced by overvoltage. These avalanches allow to investigate the influence of the own space charge on the carrier amplification above 10⁶. In the homogeneous field of a pulsed 3 cm discharge gap avalanches were produced in N₂, CH₄ and N₂+CH₄. The investigation of avalanches shows an exponential growth according to\(e^{\alpha _0 \nu _ - \cdot t} \) up to 10⁶. Between 10⁶ and ?5·10⁸ the electron avalanches increase underexponentially owing to the own space charge. These results are in accordance with former measurements in vapours. A comparison of the lowering ofα/α ₀ by the space charge with the theory allows the calculation of avalanche diameters and of the thermal energies of the electrons. The calculated values of the electron temperature vary from 2·0 to 2·5 eV for N₂, and from 1·0 to 2·0 eV for CH₄ and N₂+CH₄ atn<10⁷. Above ?·10⁷ the avalanche diameter increases considerably.     

The 2CH excitation band in C2H2–N2O and 2CH+torsion combination bands in C2H2–N2O and C2H2–CO2

A preliminary analysis of the 2CH excitation band in C₂H₂–N₂O in the 1.5 µm range (K. Didriche, C. Lauzin, P. Macko, M. Herman and W.J. Lafferty, Chem. Phys. Letters 469, 35 (2009).), only considering 117 low J-, and K_a - vibration-rotation lines, is significantly extended thanks to the analysis of new spectra including very regular series of lines with J/K_a up to 31/15. 1271 b-type lines were assigned. Perturbations are briefly discussed. The rotational temperature in the experiments is estimated to be 20?K and the upper state mean half-time is 1.6?ns for non perturbed levels. The previous analyses of the 2CH + torsion band in C₂H₂–N₂O and in C₂H₂–CO₂ (C. Lauzin, K. Didriche, T. Földes and M. Herman, Mol. Phys. 109, 2105 (2011).), are also extended to include 286 and 234 lines, respectively, also correcting for calibration errors. New rotational constants are obtained using a rigid rotor Hamiltonian by simultaneously fitting the ground, 2CH and 2CH + torsion states in C₂H₂–N₂O, and the latter state, only, in C₂H₂–CO₂.     

CH3CH2+N(4S)反应机理的理论研究

利用abinitio方法对CH3CH2+N(4S)反应进行了理论研究,在MP2/6-311+G(d,p)水平上优化得到了反应途径上的反应物、中间体、过渡态和产物的几何构型和谐振频率,并在QCISD(T)/6-311+G(d,p)水平上进行单点能计算.计算结果表明,CH2CH2+3NH和H2CN+CH3是此反应主要产物,CH3CHN+H是此反应次要产物.产物CH2CH2+3NH主要来自直接氢抽提反应通道,H2CN+CH3来自加成-解离反应通道,CH3CHN+H来自加成-解离反应通道.     

The phase diagram of single crystal [(CH3)4N]2CuBrxCl4−x solid solutions

Differential scanning calorimetry (DSC) and X-ray measurements give evidence on a complete miscibility within the solid solution system [(CH₃)₄N]₂CuBr_xCl_4−x. In addition to the known phase sequences of pure components, some new phases appear for intermidiate concentrations. Out of five triple points observed in the phase diagram, one seems to be a Lifshitz point between a paraelectric, an incommensurate and a ferroelectric phase.     

Transport properties of H–N2 mixtures

Transport coefficients (shear viscosity, volume viscosity, thermal conductivity, and mass and thermal diffusion coefficients) of H–N₂ mixtures in the dilute-gas limit have been calculated from the intermolecular potential in the temperature range 300–2000K using the classical trajectory method. The intermediate results pertaining to H–N₂ binary interactions are reported, mainly in terms of cross-section ratios. Cross-sections evaluated with the Mason–Monchick approximation yield very good results for this system, the largest deviations, about 2.5%, being observed for the thermal diffusion coefficient. The accuracy here of this approximation can primarily be attributed to a light H atom and a weakly non-spherical potential resulting in a high rotational collision number. Furthermore, we investigate to which H–N₂ cross-sections and their ratios the values of the mixture transport coefficients are most sensitive. Our results indicate that, for some cross-section ratios, reliance on universal correlations at high temperatures, often used in flame codes, can induce sizeable errors in the thermal conductivity coefficient and especially in the thermal diffusion coefficients. We also observed that the volume viscosity is particularly sensitive to the value of the cross-section for internal energy relaxation in H–N₂ collisions.     

Ozone generation in air and N2 + O2 mixtures in wire-to-cylinder reactors – an optimization attempt

The experimental results obtained with a wire-to-cylinder ozone generator (5–20 cm in length, inner diameter 12mm), using a 5 to 60 l/h flow-rate range of air or N₂ + O₂ mixtures, a negative DC high voltage being applied to the wire, are analyzed.As for the classical industrial ozonizers, the chemical engineering method, based on the energy density concept (Becker parameter = P/Q) and the global coefficients of formation K _f and destruction K _d of ozone, was applied. Some peculiar behaviours of the K _f coefficient and the role played by nitrogen and its excited levels are pointed out. The results obtained are compared with those of other authors. It appears clearly that the main parameters are not only the Becker parameter but also, and independently, the applied electrical power (P) and gas flow rate (Q) through the residence time (t _r), acting on the temperature of the reactant gas inside the reactor. It seems that t _r needs to be higher than about some seconds.As with oxygen, an optimization of the ozone production in a wire-to-cylinder ozonizer can be founded on the economical criterion = /C ² or its inverse C. more directly measurable in the usual practice.     

A computational study of N2···HHeF: comparison with N2···HArF and N2···HKrF

A weakly bound linear complex of N₂ and HHeF was found to be stable with respect to the constituent monomers by ab initio calculations at various levels of theory (MP2, MP3, MP4(SDQ) and QCISD) using a 6-311++G(2d,2p) basis set. The complex N₂···HHeF was found to have a zero-point vibrational energy corrected binding energy of 14.5?kJ mol^?1 (QCISD) and exhibits a large harmonic vibrational frequency blue shift of 375?cm^?1 for the He–H stretching vibration mode, with a diminished infrared intensity for this mode on formation of the complex. The frequency shift for this mode was also found to be very sensitive to the level of theory employed for the calculation, and is rationalized by considering intermolecular electrostatic and charge-transfer effects. The results for N₂···HHeF are compared with corresponding results for the related complexes N₂···HArF and N₂···HKrF, both of which contain the same proton acceptor molecule.     

Equation of state and structural characterization of Cu4I4{PPh2(CH2CH = CH2)}4 under pressure

Combined high pressure single crystal X-ray diffraction experiments and ab initio simulations based on the density functional theory have been performed on a copper(I) iodide cluster formulated [Cu₄I₄{PPh₂(CH₂CH?=?CH₂)}₄] under high pressure up to 5?GPa. An exhaustive study of compressibility has been done by means of determination of isothermal equations of state and structural changes with pressure at 298?K taking advantage of the single crystal is more precise than powder X-ray diffraction for this type of experiments. It allows us to report the evidence of the existence of an isostructural phase transition of second order at 2.3?GPa not detected so far.     

Formation of N2 C3Πu and B3Πg by dissociative recombination of Ar 2 + in Ar+N2 early afterglow

The hf pulse excited Ar + N₂ mixtures and early afterglow are investigated at total pressures from 266 to 1995 Pa using nitrogen of 0·05–0·5% concentration. The time-resolved intensity of Ar I atomic lines and N₂ (2nd pos., 1st pos. and 1st neg.) band systems exhibit an intense early afterglow (0·3 ms). Both the decay of electron densityn _e and that of molecular Ar ₂ ⁺ ions and enhancement of coefficient of dissociative recombination due to electron temperature decrease after the pulse lead to the formation of characteristic secondary maximum of Ar I spectral line and N₂ molecular band intensities in the momentt _m after cut-off the pulse. The values oft _m(B³_g)>t _m(C³_u)>t _m(Ar I) decrease with increasing total pressure and increase with growing concentration of N₂ in Ar. In the afterglow period the Ar ₂ ⁺ dissociatively recombine in 5p and 4p Ar states. As a result of radiative transitions the metastable Ar (³P_2,0) atoms are formed which consequently due to collisions with N₂ molecules create electronically excited N₂. With increasing nitrogen concentration this effect becomes less pronounced and at concentration of N₂ greater than 0·5% it is negligible.     

The refractivity of CO2 gas in the region of 10 μm

The refractivity of the CO₂ gas is measured with an experimental error of 2% in the 10-m region, using 10.4-m band CO₂ laser line. The frequency of the CO₂ laser is swept through the Doppler profile of the laser line. The experiment is achieved using a 0.63-m He–Ne/10.6-m CO₂-laser interferometer with a 2-m long vacuum cell. From the result, it is found that the Koch's formula also holds for the wavelengths in the 10-m region within an accuracy of 2%.     

CH4/O2/N2层流火焰瞬态响应特性数值分析

用数值分析方法研究CH₄/O₂/N₂层流扩散火焰的瞬态响应特性.采用详细的GRI-Mech 3.0机理(包含53种组分,325个基元反应)描述CH₄氧化和NO_x生成.首先比较火焰面稳态结构的计算结果和实验数据,以验证数值方法的可靠性.用台阶跃变的火焰拉伸率来模拟瞬态流场对火焰面局部结构的影响,给出了火焰面结构(温度、组分浓度)的瞬态响应曲线,分析了火焰面的响应特性.着重探讨了不同拉伸率跃变幅度对响应特性的影响,发现火焰面的响应对于拉伸率正向跃变和负向跃变并不对称,而是相反,且在小的拉伸率跃变范围内火焰面响应时间和拉伸率跃变幅度近似成反比关系.另外,温度的平均响应时间远大于一个典型湍流燃烧场的流动时间尺度,说明火焰面非稳态效应对于湍流燃烧数值模拟有重要意义.     

Dielectric relaxation in ferroelectric (CH3)2NH2AL(so4)2 · 6H2O crystal

Abstract

This paper presents the results of the investigation of dielectric dispersion and ultrasonic velocity in the ferroelectric (CH₃)₂NH₂Al(SO₄)₂ · 6H₂O crystal. The crystal shows a critical slowing down process of polarization with an extremely long relaxation time of the dipole system (τ = 1.6 · 10^?7s at the phase transition point). The dielectric response over the frequency range up to 56 GHz in the paraelectric phase can be well described in terms of a monodispersive Debye-type formula. The activation energy of dipoles in the paraelectric phase is 0.11 eV = 8.5 kT_c . The results show that the proper ferroelectric phase transition is nearly critical and of the order-disorder type.     

The candelas-weinberg model for spaces M4 × S2N

A method for calculating the one-loop effective potential for matter fields in Kaluza-Klein theories with the structure M⁴ × S^N for both even and odd N is presented. The cases M⁴ × S^N (N = 1, 2, 3, 4, 5, 6, and 8) have been examined. The method leads to finite results when N = odd and divergent results when N = even as expected.     

Vacancy Aggregation in Diamond Films grown in CH4＋H2 Atmosphere by MPCVD

Transmission electron microscopy is applied to study the diamond film grown in a CH₄ and H₂ gaseous mixture by microwave plasma assisted chemical vapour deposition. Defects in the nanometre scale, dislocation loops, arefirst observed in diamond films. The dislocation loops are found to be of co-existence with planar defects and are next to the planar defects for {111} faceting grains. A possible mechanism is suggested to interpret the co-existence of dislocation loops with planar defects.     

CH(X2∏)+N2O的反应机理研究

在G2(B3LYP/MP2/CC)理论水平上研究了CH(X^2Ⅱ)自由基与氧化二氮（NNO）分子的反应。计算了反应体系的最低二重态势能面上各驻点的构型参数、振动频率和能量，揭示了此反应存在的两种机理和六个通道。基中HC和NNO复合，生成中间体HC(N)NO，解离得到产物HCN+NO，这是最主要的通道之一；HC插入NO键，克服38.9kJ/mol的势垒，产生富能的中间体HC(O)NN，预测了五个反应通道，其中主要反应通道为：NN+HCO.     

Magnetic transitions in K2MnCl4·2H2O

Results of (dM/dH) measurements on tetrahedral K₂MnCl₄·2H₂O as a function of temperature and magnetic field, are presented. An antiferromagnetic transition along the tetragonal axis is observed at T_N = (3.05±0.05) K. The H-T magnetic phase diagram was completely determined, and shows the usual characteristics of that of a low anisotropy antiferromagnet. The T = 0 critical fields are compatible with the values H_E = (29.2±0.3) kOe and H_A = (5.9±0.6) kOe for the exchange and anisotropy fields.     

Collision-induced absorption in the V2 fundamental band of ^12CH4

The integrated intensities of the collision-induced absorption of the V2 band of ^12CH4 perturbed by Ar have been calculated theoretically using the ab initio calculations, and the value of the quadrupole transition moment we obtained is （0/Q/V2） = 5.226ea^2.. The corresponding experimental value obtained from ^12 CH4-Ar spectra is /〈0/Q/V2）/ = 4.931ea^2. Ignoring vibration-rotation interaction and Coriolis interaction, and considering both the theoretical approximations and experimental uncertainties, the agreement can be regarded as good, thus confirming that the enhancement is due to the quadrupole collision-induced mechanism.[第一段]