Vibrationally inelastic scattering of H∼ ions from H2, N2, O2 and CO2

State-resolved measurements are presented for vibrational excitation of H₂, N₂, O₂ and CO₂ by H^? impact in the collision energy rangeE _cm=20–180 eV and for scattering in the forward direction (0±0.5°). The data obtained from the measurements are the relative intensities and differential cross sections for vibrational excitation up toν′=4, the transition probabilitiesP _0→ν′ and the vibrational energy transferΔE _vib. For the systems H^?-H₂, N₂, O₂ the vibrational inelasticity increases in the order H₂-N₂-O₂. The mechanism for vibrational excitation in these systems is due to transient charge transfer from the H^? ion into antibonding orbitals of the target molecule which provides a bond stretching force during the collision. For H₂ and N₂, the results are compared with corresponding measurements for H⁺ scattering where the interaction mechanism is quite different. In the case of CO₂, vibrational excitation in forward scattering is caused primarily by the long-range dipole interaction. The spectra are very similar for H^?-CO₂ and H⁺-CO₂. Finer details are attributed to the influence of transient charge transfer and valence interactions.     

A theorem for the distribution functions of hard-sphere fluids

The thermal diffusion factor α_T for the gas mixtures N₂-CO₂, Ar-CO and Ar-NO has been measured as functions of temperature and composition by the two-bulb method. As at least one of the components of the mixture is diatomic or triatomic the thermal diffusion factor is likely to be influenced by inelastic collision. The α_T data have been analysed in terms of the available elastic and inelastic theories. The results show the comparatively small effect of inelastic collision on thermal diffusion. The necessity of using more realistic intermolecular potentials to interpret α_T data has been pointed out.     

Thermal diffusion and the approach to the steady state in gases: II

The theory of the rate of approach to the steady state in themal diffusion is tested experimentally on the systems He-Ar, He-CO₂, H₂-CO₂, and D₂-CO₂ over a temperature range of about -78°c to 325°c. The course of the diffusion has been followed by means of the radioactive tracers ³⁷Ar and ¹⁴CO₂. The theory appears to be verified, and the results are used to calculate ordinary diffusion coefficients, which are in reasonable accord with previous measurements by other techniques. The thermal diffusion factors, which are obtained from the same measurements, also appear to have reasonable accuracy. The experimental method therefore appears to have promise as a sensitive method for the determination of forces between unlike molecules.     

模拟退火研究CO2在Ar团簇中的结构和能量性质

采用模拟退火算法研究了范德华团簇Ar_N-CO₂(N=1～19)的结构和能量性质. 利用一个最近得到的Ar-CO₂的势能面及Aziz的Ar-Ar作用势能,采用两体加和近似来构建团簇的高维势能面,再根据一个精心设计的退火进度表来采样玻璃态相空间以得到最低能量构型.与其他较轻的稀有气体形成的Rg_N-CO₂团簇不同,Ar-CO₂团簇表现出特有的结构和能量性质,比如小尺度团簇的相关性质     

Infrared spectrum of the continuum and dimer absorption in the vicinity of the O2 vibrational fundamental in O2/CO2 mixtures

The intensities of the collision-induced absorption (CIA) bands associated with the electric-dipole forbidden O₂ fundamental and the CO₂ν₁/2ν₂ Fermi dyad monomer vibrational bands have been studied over the temperature range 193-360 K and the frequency range 1100-2000 cm⁻¹. As CO₂ is added to a pure O₂ sample, the intensity in the O₂ fundamental band region increases dramatically. At the lowest temperature studied, 193 K, the band-integrated CIA coefficient for enhancement of the Fermi dyad absorption from CO₂ to CO₂ collisions, S_CO2-CO2, is more than a factor of two larger than the band-integrated CIA coefficient for enhancement of the O₂ vibrational fundamental by CO₂ collisions, S_O2-CO2. Moreover, the S_CO2-CO2 coefficient shows a significantly larger temperature dependence, increasing by more than a factor of two from 345.6 to 193 K while S_O2-CO2 increases by less than one third. The band shapes and their temperature dependence provide clear evidence for the formation of CO₂-CO₂ and CO₂-O₂ complexes. The CO₂-CO₂ dimer feature is most striking, contributing significantly to the infrared absorption near the expected CO₂ monomer fundamentals. Evidence for the more weakly bound CO₂-O₂ complex is seen on the O₂ CIA band, particularly at the lowest temperatures studied. The shapes for both dimer bands display sharp a-type Q branch central profiles and broad P and R branch like structure attributed to b-type Q branches for the CO₂-CO₂ complex and a-type P and R branch structure for the CO₂-O₂ complex. The present results stress the importance of including bound and metastable dimer absorption in any theoretical modeling of CIA, particularly when one of the collision partners has a large electrostatic moment, such as CO₂ with its large electric quadrupole moment.     

Structural,elastic, electronic,optical and thermal properties of c-SiGe<Subscript>2</Subscript>N<Subscript>4</Subscript>

We have investigated the structural, elastic, electronic, optical and thermal properties of c-SiGe₂N₄ by using the ultrasoft pseudopotential density functional method within the generalized gradient approximation. The calculated structural parameters, including the lattice constant, the internal free parameter, the bulk modulus and its pressure derivative are in agreement with the available data. The independent elastic constants and their pressure dependence, calculated using the static finite strain technique, satisfy the requirement of mechanical stability, indicating that c-SiGe₂N₄ compound could be stable. We derive the shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients for ideal polycrystalline c-SiGe₂N₄ aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of this compound from the average sound velocity. Band structure, density of states, Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, in order to understand the optical properties of c-SiGe₂N₄, the dielectric function, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermal effects on some macroscopic properties of c-SiGe₂N₄ are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have obtained successfully the variations of the primitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first time, the numerical estimates of the elastic constants and related parameters, and the thermal properties are performed for c-SiGe₂N₄.     

Rotational CARS for simultaneous measurements of temperature and concentrations of N2, O2, CO, and CO2 demonstrated in a CO/air diffusion flame

Rotational coherent anti-Stokes Raman spectroscopy (CARS) has over the years demonstrated its strong potential to measure temperature and relative concentrations of major species in combustion. A recent work is the development and experimental validation of a CO₂ model for thermometry, in addition to our previous rotational CARS models for other molecules. In the present work, additional calibration measurements for relative CO₂/N₂ concentrations have been made in the temperature range 294-1246 K in standardized CO₂/N₂ mixtures. Following these calibration measurements, rotational CARS measurements were performed in a laminar CO/air diffusion flame stabilized on a Wolfhard-Parker burner. High-quality spectra were recorded from the fuel-rich region to the surrounding hot air in a lateral cross section of the flame. The spectra were evaluated to obtain simultaneous profiles of temperature and concentrations of all major species; N₂, O₂, CO, and CO₂. The potential for rotational CARS as a multi-species detection technique is discussed in relation to corresponding strategies for vibrational CARS.     

基于反转法的O2-CO2 输运性质预测

采用反转法计算得到了O₂-CO₂混合气体新的势能参数.在此基础上,根据分子动力学理论,计算了混合气体在零密度下的输运性质,包括黏度系数、热扩散系数和热扩散因子,计算的温度范围为273.15—3273.15 K.与实验值比较表明,计算结果可以满足实际工程应用.     

Second virial coefficient for a mixture of nonspherical molecules of arbitrary symmetry

The mixture and interaction second virial coefficients of a binary gas mixture of nonspherical molecules of arbitrary symmetry have been calculated for a set of unlike force parameters which is obtained from the force parameters for like interactions by using empirical combination rules. In the calculation molecular anisotropy of very general type has been accounted. The relative contribution of each branch of interactions has been evaluated as a function of temperature. The theoretical values of interaction second virial coefficient have been compared with the experimental data of N₂+A, N₂+He, N₂+H₂, N₂+O₂, N₂+C₂H₄, N₂+C₂H₆, CO₂+A, CO₂+H₂, CO₂+N₂, CO₂+O₂, CO₂+CO, CO₂+C₂H₄, CO₂+C₂H₆, O₂+A and H₂+CO. The agreement between theory and experiment is satisfactory for all the systems. Numerical estimations of the mixture second virial coefficients as a function of temperature and composition are given for the systems CO₂+A, CO₂+H₂, CO₂+N₂, CO₂+O₂ and CO₂+CO.     

Determination of the electron concentration and temperature,as well as the reduced electric field strength,in the plasma of a high-voltage nanosecond discharge initiated in atmospheric-pressure nitrogen by a runaway electron beam

We report on the results of spectroscopic measurements of electron concentration N _e and temperature T _e , as well as the reduced electric field strength E/N in the plasma of a high-voltage nanosecond discharge in the gap with a strongly nonuniform electric field distribution, which is filled with nitrogen under the atmospheric pressure. The possibility of using the method for determining T _e and E/N, which is based on the determination of the ratio of the peak intensities of the ionic N ₂ ⁺ (λ = 391.4 nm) and molecular N₂ (λ = 394 nm) nitrogen bands, is proved. We detected the mean values of quantities N _e , T _e , and E/N amounting to ～2 × 10¹⁴ cm^?3, ～2 eV, and ～240 Td, respectively. In addition, the dynamics of these quantities is determined.     

Carboxylation of aromatic compounds in a supercritical carbon dioxide medium

The reaction of direct carboxylation of benzene and its derivatives PhX (X = Me, Br, Ph, OPh, OMe), as well as mesitylene, durene, and ferrocene, in a supercritical CO₂ medium in the presence of various Lewis acids (AlCl₃, FeCl₃, ZrCl₄, and ZnCl₂) is studied. It is shown that, in all cases, secondary reactions proceed faster than the primary reaction of carboxylic acid formation. For the thoroughly studied AlCl₃-CO₂toluene system, optimal conditions of the formation of n-toluic acid are determined. For the AlCl₃-CO₂-benzene system, as an example, quantum-chemical calculations of the characteristics of the allowed pathways of the carboxylation reaction are performed.     

Opto-galvanic spectroscopy of some molecules in discharges: NH2, NO2, H2 and N2

The change of the discharge voltage when laser light crossing the discharge is tuned to a molecular transition has been measured. Experiments have been performed in the wavelength region between 570 nm and 620 nm with discharges in NH₃, NO₂, H₂, N₂, O₂ and argon. Transitions from the ground states of NH₂ and NO₂ and transitions from metastable states of N₂ and H₂ have been detected. The spacial dependence of the opto galvanic in a low pressure dc-discharge of H₂ and N₂ has been studied.     

μ+ SR studies on pure MnF2 and site-diluted (Mn0.5Zn0.5)F2SR studies on pure MnF2 and site-diluted (Mn0.5Zn0.5)F2

Positive muon spin rotation and relaxation measurements have been carried out on the antiferromagnets, pure MnF₂ and site-diluted (Mn_0.5Zn_0.5)F₂, above and below the Néel temperature T_N using single-crystal specimens. Two different muon signals have been found in the pure MnF₂; with the precession frequency υ_A for the site A and υ_B for the site B measured in zero external magnetic field at T=5 K. We propose a picture that the signal from the A site represents the “muonium” state, and discuss the characteristic features of muonium in magnetic materials. The spin relaxation rate 1/T₁, measured in zero external field, decreases rapidly with decreasing temperature below T_N. The mechanism of the spin relaxation above T_N is explained by the exchange fluctuations of the Mn moments, while below T_N by the Raman scattering of spin waves. At the same normalized temperature T/T_N, 1/T₁ observed in the diluted (Mn_0.5Zn_0.5)F₂ is significantly larger than that in the pure MnF₂ below T_N. The difference between the pure and diluted systems is related to the large spectral weight of low-energy magnons in (Mn_0.5Zn_0.5)F₂ found by neutron scattering.     

The absorption cross sections of N2, O2, CO,NO, CO2, N2O,CH4, C2H4, C2H6 and C4H10 from 180 to 700Å

The absorption cross sections of N₂, O₂, CO, NO, CO₂, N₂O, CH₄, C₂H₄, C₂H₆, C₄H₁₀ have been measured photoelectrically in the 180–700 Å region using synchrotron radiation. The absorption cross sections in the region λ ≥ 500 Å was found to be structureless and to increase monotonically with wavelength for all gases. The positions of the structure observed in the 520–720 Å region for N₂, O₂, CO₂ and N₂O are consistent with the various Rydberg series reported by previous authors.     

Low temperature thermoelectric power of LaB6, PrB6 and NdB6

We have measured the thermoelectric power of LaB₆, PrB₆ and NdB₆ in the temperature range 2–20K. PrB₆ and NdB₆ order antiferromagnetically at T_N = 6.99K and 7.74K respectively, whereas LaB₆ is non-magnetic. The thermoelectric power data have a negative maximum near 5.5K in all three hexaborides. This negative peak is thought to be mainly due to phonon drag in LaB₆. In PrB₆ and NdB₆ there is an additional contribution due to magnon drag. It is expected that the high temperature thermoelectric power is mainly due to an electron diffusion term and a contribution due to spin disorder scattering. The thermoelectric power and the resistivity have been compared in the vicinity of T_N. A qualitative similarity in the temperature derivatives of these two quantities has been found for PrB₆ and NdB₆ near T_N.     

Laser schlieren measurement of vibrational relaxation times for N2O in mixtures containing CO,N2, and Ar behind a shock wave

The laser schlieren method has been used behind shock waves where the temperatures are 410–2400°K to measure the vibrational relaxation times for N₂O and also for mixtures of N₂O with CO, N₂, and Ar. The vibrational relaxational times of N₂O have been measured for collisions with these partners, and it has been found that the effectiveness of N₂ in relaxation is close to that of N₂O, whereas CO results in accelerated vibrational relaxation of N₂O. A comparison is made with the available published data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–8, November, 1984.We are indebted to V. V. Savkin for performing the mass spectral analyses.     

Raman spectroscopic study of a laminar hydrogen diffusion flame in air

Spontaneous Raman spectroscopy has been employed for time-averaged, spatially-resolved measurements of temperature and species concentration in an axisymmetric, laminar hydrogen diffusion flame in quiescent air. Temperatures were obtained from vibrational Q-branch raman spectra of N₂, O₂, and H₂ and the rotational Raman spectra of N₂ and H₂, and concentrations of H₂, and N₂ were determined. The results are compared to existing numerical nonequilibrium calculations for the conditions of this experiment. Significant differences between experimental and predicted temperature and concentration profiles are observed. In particular, the flame is larger in both diameter and length and the flame zone is thicker than predicted. Some possible sources of the discrepancies are discussed.     

Infrared absorptions and band widths of dilute solutions of CF3H in liquid Ar,N2, and Xe

The spectra of fluoroform (CF₃H) in the solvents Ar, N₂, and Xe have been obtained in the fundamental region (400–4000cm^?1) using a low temperature cryostat and a Fourier transform infrared spectrophotometer. Ab initio calculations at the HF/6-31G? level have been performed to obtain the calculated vibrational frequencies of the isolated CF₃H molecule and CF₃H in the presence of the solvents (Ar, N₂, and Xe). Comparison of the frequency shifts of CF₂H in solution with respect to the gas phase frequencies is made for the experimental and theoretical results. Lorentzian functions were used to fit the bands and obtain the wavenumber at the peak absorbance and the vibrational band widths. An analysis of the dynamics of relaxation has been made based on the infrared time correlation functions for three of the fundamental modes (ν₁, ν₃, and ν₄). Bandwidths, band moments, and relaxation times were obtained by appropriate fitting of the experimental correlation functions to theoretical models. In liquid argon, the temperature dependence of the second moment (M ₂) indicates that rotational relaxation explains the bandwidth of the ν₃ mode. For the ν₄ mode, the temperature dependence of M ₂ can be attributed to rotational relaxation if it is corrected with a Coriolis coupling term. The bandwidths of the ν₁ mode do not follow the rotational relaxation model, and probably vibrational relaxation is the dominant mechanism.     

YBa2Cu3O7-x高温导电性的研究

本文将以YBa₂Cu₃O_7-x的高温实验为基础,分析和讨论了氧对YBa₂Cu₃O_7-x高温导电性的影响以及一维Cu—0链的导电作用。还报道了一种新现象,即在高温下,一旦氮气被换成氧气,YBa₂Cu₃O_7-x就迅速地发生从半导体到金属的结构相变。 关键词：     

The viscosity and diffusion coefficients of eighteen binary gaseous systems

The paper reports accurate measurements of the viscosity of the eighteen binary gaseous systems: CF₄ with He, Ne, Ar, N₂, CO₂, CH₄; SF₆ with He, Ne, Ar, N₂, CO₂, CH₄, CF₄ and O₂ with He, Ne, CO₂, CF₄, SF₆. The measurements were performed in a high-precision oscillating-disk viscometer at atmospheric pressure and in the temperature range 25–200°C for the systems containing CH₄ or SF₆ and in the temperature range 25–400°C for the remainder. The reported viscosities are believed to be accurate to within ±0.1% at room temperature and to within ±0.2% at 400°C.It is shown that the data conform to the extended law of corresponding states developed by Kestin, Ro and Wakeham despite the complexity of some of the component gases. The standard deviation between the experimental values and those calculated from the law of corresponding states is only 0.3% which is commensurate with the uncertainty in the experimental results.Binary diffusion coefficients derived from the mixture viscosity data are also presented; they have an estimated uncertainty of ±2%.