Wing profile measurements of the Na-doublet lines in C2H2/O2/N2, H2/O2/N2 and H2/O2/Ar frames at 1 atm

Fluorescence-excitation (wing) profiles of the Na-D doublet lines were measured over a wavelength range extending from 0.3 to 200 Å from the line center for the red D₁ and blue D₂ wings and from 0.3 to 3 Å for the red D₂ and the blue D₁ wings, respectively. The line profiles were determined with the aid of a tunable CW dye-laser as a background source by measuring the total fluorescence intensity observed on detuning the laser wavelength. The flames were premixed, laminar, shielded flames at 1 atm, with temperatures ranging from 1860 to 2270 K; N₂ and Ar served as diluent gases. The line core and near-wing profiles (i.e. the region covering 0.3<Δλ<7 Å for the outer wings and 0.3<Δλ<3 Å for the inner ones) in all of the flames studied appeared to have the same frequency dependence, regardless of the nature and concentrations of the gases used. The blue D₂-line profile followed an unexpected (-2.2) law, while the other three profiles obeyed the theoretically expected (-2) law (the dispersion profile function). The line profile in the Δλ range between the impact and quasistatic regions was found to depend on the main perturbers involved. We found that the far blue D₂- and red D₁-wings in the Ar-diluted H₂/O₂ flame obeyed the (-$\text{5}\text{4}$) and (-$\text{3}\text{2}$) laws, respectively, as predicted by the quasi-static theory for the Lennard-Jones interaction. For the N₂-diluted C₂H₂/O₂ and H₂/O₂ flames, we did not find these wing dependences in the Δλ range investigated.     

Magnetic properties of NdCo2Ge2, ErCo2Ge2 and PrFe2Ge2 compounds

Magnetometric and neutron diffraction studies of polycrystalline NdCo₂GE₂, ErCo₂Ge₂ and PrFe₂Ge₂ compounds were carried out in the temperature range between 4.2 and 300 K. All samples are antiferromagnetic with Néel temperature 26.5, ～ 4.2 and 13 K, respectively. The RECo₂Ge₂ compounds have collinear antiferromagnetic order of +?+? type. For PrFe₂Ge₂ a sinusoidal magnetic structure is observed. Magnetic moment is localized on RE atoms only and is equal to that of RE³⁺ free ion value. In ErCo₂Ge₂ the magnetic moment of Er atoms is perpendicular to the c-axis, whereas for remaining compounds it is parallel to the c-axis.     

Les phases Cd2Nb2-2xSn2xO7-2xF2x

The solid solution Cd₂Nb_2-2xSn_2xO_7-2xF_2x is studied by X-Ray diffraction and Mössbauer spectroscopy. Two phases I and II are observed; phase I presents a normal pyrochlore structure but phase II shows a local order around Sn⁴⁺. The difference between phases I and II is explained by the difference of electronic configuration between Sn⁴⁺ (4d¹⁰) and Nb⁵⁺ (4d⁰).     

Neutron diffraction study of magnetic ordering in PrCu2Si2, PrCu2Ge2, PrFe2Ge2 and NdFe2Ge2

A neutron diffraction study of polycrystalline PrCu₂Si₂ [1], PrCu₂Ge₂ [2], PrFe₂Ge₂ [3] and NdFe₂Ge₂ [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below T_N = 19 ± 1 K [1], T_N = 16 ± 1 K [2], T_N = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu₂Si₂ and PrCu₂Ge₂ and +--+ for PrFe₂Ge₂ and NdFe₂Ge₂. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field.     

Combustion properties of H2/N2/O2/steam mixtures

The present work reports new experimental and numerical results of the combustion properties of hydrogen based mixtures diluted by nitrogen and steam. Spherical expanding flames have been studied in a spherical bomb over a large domain of equivalence ratios, initial temperatures and dilutions at an initial pressure of 100 kPa (T_ini = 296, 363, 413 K; N₂/O₂ = 3.76, 5.67, 9; %Steam = 0, 20, 30). From these experiments, the laminar flame speed $S_L^0$, the Markstein length L’, the activation energy Ea and the Zel'dovich β number have been determined. These parameters were also simulated using COSILAB^® in order to verify the validity of the Mével et al. [1] detailed kinetic mechanism. Other parameters as the laminar flame thickness δ and the effective Lewis number Le_eff were also simulated. These new results aim at providing an extended database that will be very useful in the hydrogen combustion hazard assessment for nuclear reactor power plant new design.     

Structure and properties of Bi2Sr2CaCu2Ox/Bi2Sr2CuOx superlattices prepared by RF magnetron sputtering

We have prepared Bi₂Sr₂CaCu₂O_x/Bi₂Sr₂CuO_x (2212/2201) superlattices with various stacking periodicity by multitarget RF magnetron sputtering. Their crystal structure and electrical properties were investigated. The superlattice was found to be successfully constructed from the data of XRD patterns, AES, etc. The critical temperature increased almost linearly with increasing thickness of the 2212 phase up to a thickness of 6 unit cells. On the other hand, it did not decrease as the thickness of the 2201 layers was increased. The unit cell/unit cell superlattice showed T_{c zero} of 30 K.     

Magnetic properties of the compounds ThCO2Ge2 and ThCo2Si2

Rather old preparation of the compounds ThCo₂Ge₂ and ThCo₂Si₂ and their magnetic study in the temperature range 100–570 K, published by Omejec and Ban [Z. Anorg. Allg. Chem. 380 (1971) 111], indicated that both compounds ordered ferrromagnetically below 100 K. In order to verify the old data, polycrystalline samples of ThCo₂Ge₂ and ThCo₂Si₂ have been prepared by arc melting and subsequent annealing, and studied by X-ray diffraction at room temperature (RT), by superconducting quantum interference device (SQUID)-magnetization and AC-susceptibility measurements at 2–320 K, and by dc-magnetization measurements in variable magnetic fields up to 120 kOe at 5, 80, and 283 K. The magnetic measurements confirm the ferromagnetic ordering in both compounds, but with totally different Curie temperatures: ≈120(20) K for ThCo₂Ge₂ and above 320 K for ThCo₂Si₂. The paramagnetic values of ThCo₂Ge₂ and the ordering of both compounds are discussed and compared with the old results of Omejec and Ban.     

碱金属Li,Na,K,Rb,Cs,Fr的ns2S1/2,np2P1/2,3/2, nd2D3/2,5/2 和nf2F5/2,7/2 里德伯能级理论研究

本文在多通道量子数亏损理论(MQDT)框架下,利用相对论多通道理论(RMCT),分别在冻结实近似、 考虑Δl=-1的偶极极化效应、Δl=+1的偶极极化效应、Δl=± 1的偶极极化效应、伸缩模效应以及同时考虑偶极极化效应和伸缩模效应等不同层次近似下,系统地计算了碱金属Li, Na, K, Rb, Cs和Fr七个里德伯系列的能级,即ns²S_1/2, np²P_1/2, np²P_3/2, nd²D_3/2, nd²D_5/2, nf²F_5/2 和nf²F_7/2.计算结果表明,电子关联效应对碱金属原子的里德伯能级的影响很大.总的来说,偶极极化效应比伸缩模效应重要,而在偶极极化效应中, Δl = + 1的偶极极化效应比Δl = - 1的偶极极化效应重要.但对于Na的ns²S_1/2,(nd²D_3/2,nd²D_5/2)里德伯系列的能级,和Li的(np²P_1/2,np²P_3/2)里德伯系列的能级,是伸缩模效应比较重要.     

Magnetic properties of ternary RMn2Si2 and RMn2Ge2 compounds

Magnetic properties of RMn₂Si₂ and RMn₂Ge₂ compounds, where R is a rare earth metal, have been investigated by magnetometric measurements. RMn₂Ge₂ (where R is a light rare earth) and LaMn₂Si₂ are ferromagnets. Remaining compounds have antiferromagnetic properties. DyMn₂Si₂ and ErMn₂Si₂ show ferromagnetic properties at low temperatures. It was confirmed that the value of Curie (or Néel) temperature for the Mn sublattice decreases with increasing c constant.     

Oscillator strengths and transition probabilities of the Be(I) isoelectronic sequence for 2p2-2s2p and 2s2p-2s2 transitions

Oscillator strengths and transition probabilities are obtained from an intermediate coupling scheme. The initial basis of the eigenstates is formed inLS-coupling. To obtain the resulting energy matrix,Z^-1 perturbation theory is applied. The values of oscillator strengths and transition probabilities for 1s²2p²?1s²2s2p and 1s²2s2p?1s²2s² transitions are calculated and the comparison is made with some recent results. The nuclear charges (Z) involved varied fromZ=4(Be(I)) toZ=35(Br(XXXII)).     

Magnetic structures of PrCO2Si2 and TbCo2Si2 compounds

Neutron diffraction studies of polycrystalline PrCo₂Si₂ and TbCo₂Si₂ compounds were carried out at 4.2 and 293 K. Both samples have collinear antiferromagnetic order below T_N(31(1) and 46(1) K for Pr and Tb compound respectively), with their magnetic moments parallel to the c axis. The ordered magnetic moment values of Pr and Tb at 4.2 K (3.19 and 9.12 μ_B respectively), are close to the saturation value of the free ions. The corresponding magnetic space group P_l4/mnc (Sh⁴¹⁰₁₂₈) is body-anticentered ($\text{k =}\text{111}\text{222}$ refering to P_l cell).     

Neutron diffraction study of magnetic ordering in ErMn2Si2, ErMn2Ge2 and ErFe2Si2

Neutron diffraction study of polycrystalline compounds ErMn₂Si₂, ErMn₂Ge₂ and ErFe₂Si₂ was performed in the temperature range between 1.8 and 293 K. All compounds have tetragonal, ThCr₂Si₂-type crystal structure. The antiferromagnetic collinear structure of ErMn₂Si₂ and ErMn₂Ge₂ at both RT and LNT, consists of a sequence + - + - of ferromagnetic layers of Mn atoms. The magnetic moment of an Mn atom (≈2μ_B) is parallel to the c-axist. At low temperatures (LHT and lower), the ferromagnetic ordering within the Er sublattice is observed. The magnetic moment (μ_Er ≈ 9μ_B) is perpendicular to the c-axis. From the temperature dependence of the intensities of the magnetic peaks, the following values for the Curie temperatures were obtained: (10±5) K for ErMn₂Si₂ and (8.5±3) K for ErMn₂Ge₂. For ErFe₂Si₂ a collinear antiferromagnetic structure of the + - - + type was found, the magnetic unit cell consisting of the chemical one, doubled along the c-axis.     

Orbital ordering in Mott-insulators La2O3Fe2Se2 and La2O3Co2Se2

The electronic structure and magnetic properties of new layered oxyselenide compounds La₂O₃Fe₂Se₂ and La₂O₃Co₂Se₂ are studied by first-principles calculations. Our results indicate that both compounds are Mott-insulators with orbital ordering. The ground states of both compounds are the checkerboard antiferromagnetic states, which are different from the iron pnictide superconductors, although their structures are similar to those of the Fe-As-based superconductors.     

Transport properties of single crystals of CeCu2Si2 and CeNi2Ge2

The resistivity, thermopower and thermal conductivity were measured on single crystals of CeCu₂Si₂ and CeNi₂Ge₂ between 60mK and 300 K. All transport anomalies associated with the unstable 4f-shell in Ce are strongly anisotropic in these noncubic systems.     

Structure, transport and magnetic properties in La2xSr2−2xCo2xRu2−2xO6

The perovskite solid solutions of the type La_2xSr_2−2xCo_2xRu_2−2xO₆ with 0.25≤x≤0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for x=0.4 and 0.6. Most importantly, low field (50 Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate the presence of Co²⁺/Co³⁺ and Ru⁴⁺/Ru⁵⁺ redox couples in all compositions except x=0.5. Presence of magnetic ions like Ru⁴⁺ and Co³⁺ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization.     

Adsorption-desorption studies using ESD of CCl2F2, C2H2F2 and C2F6 on tungsten

The behavior of the desorbing F⁺ ion current from electron bombarded CCl₂F₂, C₂H₂F₂ and C₂F₆ adsorbed on tungsten has been used to investigate the processes of adsorption and desorption of these gases. For tungsten near room temperature, measurements of the F⁺ ion current as a function of electron bombardment time indicated very similar or even identical F⁺-yielding adsorbed species resulting from adsorption of either CCl₂F₂ or C₂H₂F₂ and widely different species from C₂F₆. Cl⁺ ions were also observed to desorb from CCl₂F₂ ad-layers. The behavior of the Cl⁺ ion current with time during electron bombardment indicated electronic conversion between adsorbed binding modes. Complementary investigations on the interaction of CCl₂F₂, C₂H₂F₂ and C₂F₆ with tungsten were carried out by thermal desorption experiments in which the F⁺ ion signal was used to observe the coverage decrease of the F⁺-yielding species. The experiments were performed at tungsten temperatures in the 1200–1600 K range. It was concluded that the F⁺-yielding adsorbed species from CCl₂F₂ and C₂H₂F₂ were strongly bound to the tungsten surface. The F⁺-yielding species from C₂F₆ were found to be weakly bound. From a comparison of the ESD and thermal desorption results, the possibility of dissociative adsorption as well as the nature of the adsorbed species is discussed.     

N2- and O2-broadening coefficients of C2H2 IR lines

Pressure-broadening parameters of six lines belonging to the ν₅ band of C₂H₂ in collision with N₂ have been measured with a tunable diode-laser spectrometer in order to complete up to J = 33 our earlier measurements (D. Lambot, G. Blanquet, and J. P. Bouanich, J. Mol. Spectrosc.136, 86–92 (1989)) on the broadening of C₂H₂ by N₂ and O₂ at 297 K. These N₂- and O₂-broadening coefficients have been first calculated on the basis of the Anderson-Tsao-Curnutte theory; in this approach, we show that the short-range interactions which contribute significantly to the linewidths are not correctly treated. Next, we consider the improved semiclassical model proposed by Robert and Bonamy. The intermolecular potential consists in the addition of the atom-atom interaction model to the quadrupolar interactions. The limited radial spherical harmonics expansion of the atom-atom potential, from which expressions for the differential cross section were derived, appears to be quite insufficient at short intermolecular distances. Therefore, we use a more accurate representation of this potential, avoiding an inadequate truncation and keeping the analytic expressions obtained by Bonamy and Robert. In the calculations we take into account the contributions derived from the radial functions U₀₀₀(r), U₂₀₀(r), and U₂₂₀(r), as well as from U₄₀₀(r). A theoretical expression is obtained for the U₄₀₀ contribution to the differential cross section. The results of the calculations arising from the exact radial expansion of the atom-atom potential appear to be significantly larger for high J lines than those arising from the truncated expansion. The latter results, which do not include adjustable atom-atom parameters, are in good agreement with experimental broadening coefficients for C₂H₂---O₂ and in reasonable agreement (except at large J values) for C₂H₂---N₂. It is also shown that the contributions to the linewidths derived from U₄₀₀ are rather small for C₂H₂---N₂ and more important for C₂H₂---O₂. Finally, by calculating the collisional linewidths of C₂H₂---N₂ and C₂H₂---O₂ at 200 K, we have predicted their temperature dependences.     

CO在MoS2/K2CO3/TiO2上的加H2反应

根据“盐类及氧化物等在高比表面载体上有自发分散倾向”的原理，制备了一种新型的用于由合成气（H2／CO）合成甲醇的催化剂MoS2/K2CO/TiO2(DSA),该催化剂具有较好的耐硫性和对甲醇有较高的选择性，通过对反应条件的教察得出结论：高压、低温、高空速有利于提高醇的选择性。     

Structural study of the Lu2Si2O7-Sc2Si2O7 system

Different compositions in the Lu₂Si₂O₇-Sc₂Si₂O₇ system have been synthesized following the ceramic method. All XRD patterns are compatible with the thortveitite structure (β-RE₂Si₂O₇ polymorph). Unit cell parameters change linearly with composition, which indicates a complete solid solubility of Sc₂Si₂O₇ in Lu₂Si₂O₇. ²⁹Si MAS NMR spectra show a decrease of the ²⁹Si chemical shift with increasing Sc content. A correlation reported in the literature to predict ²⁹Si chemical shifts in silicates is applied here to obtain the theoretical variation in ²⁹Si chemical shift values in the system Lu₂Si₂O₇-Sc₂Si₂O₇ and the results compare favourably with the values obtained experimentally. The FWHM values of the ²⁹Si MAS NMR curves indicate a random distribution of Lu and Sc in the structure of the intermediate members. Finally, the IR study of the system confirms the solubility of Sc₂Si₂O₇ in Lu₂Si₂O₇, showing the splitting of several modes in the intermediate members and a linear shift of the frequency on going from one end-member to the other.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.