Near-Threshold Low Rydberg Depletion Spectroscopy of H2, D2, and HD

Using high-resolution depletion spectroscopy, we have experimentally studied the physics of near-threshold low Rydberg states of all three stable isotopic variants of molecular hydrogen. The experiments were required to calibrate the absolute wavelength, including several transitions from the EF (v = 0) and EF (v = 6 or v = 9) to the same low-n Rydberg states. The measurements have been performed for several initial rotational levels in all three stable isotopic variants. Transitions to very high vibrational levels of the B, Bt, and C states have been measured with accuracy 0.002cm^-1. The pulsed amplifier perturbations were also measured by opticalhe terodyne methods.     

Optical,thermal, and structural properties of Nb2O5–TeO2 and WO3–TeO2 glasses

Glass samples from two systems, Nb₂O₅–TeO₂ and WO₃–TeO₂, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb₂O₅ decreased the density while increase in the WO₃ concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb⁵⁺ and W⁶⁺ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb₂O₅ and WO₃ mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO₄ units decreased with the increase in Nb₂O₅ and WO₃ concentrations.     

Molecular Dynamics Study of gases H2,D2 and T2

The classical Molecular dynamics simulation has been used to study the equation of state of gas H2,D2 and T2.It has also been investigated that the isotope mass affects on the accuracy of equation of state.Our calculated Iesults show that the classical effect is principal and the isotope mass effects on the equation of state are obvious for the much light gases.At the same time,some useful theoretical data of equation of state for these gases have been provided.It is found that the classical simulation is still effective to the quantum gas.However,the quantum mechanics simulation and the improvement of intermolecular interaction potential are necessary if more accurate computational results are expected.     

Laser induced breakdown of Ar,N2 and O2 gases using 1.064, 0.532, 0.355 and 0.266 μm radiation

An experimental investigation of laser-induced breakdown using Nd:YAG laser harmonics for argon, nitrogen and oxygen gases is reported. Pressure dependence as well as wavelength dependence of the breakdown threshold irradianceI _th is investigated. The experimental observations for 1.064 and 0.532 m laser wavelengths are in agreement with theoretical calculations which include the effects of multiphoton ionization and cascade ionization.     

Enthalpy of formation of LiNiO2, LiCoO2 and their solid solution,LiNi1−xCoxO2

LiCoO₂, LiNiO₂ and their solid solution, LiNi_1−xCo_xO₂, are important cathode materials for lithium ion batteries. Samples in this system were synthesized by solid state reaction of Co₃O₄, NiO and Li₂CO₃ or LiOH·H₂O. Their lattice parameters were determined by Rietveld refinement. High temperature drop solution calorimetry in molten 3Na₂O·4MoO₃ and 2PbO·B₂O₃ solvents at 974 K was performed to determine the enthalpy of formation from the constituent oxides plus oxygen and the enthalpy of mixing in the solid solution series. There are approximately linear correlations between the lattice parameters, the enthalpy of formation from oxides (Li₂O, NiO and CoO) plus O₂ and the Co content in the compounds. The solid solution of LiCoO₂ and LiNiO₂ is almost ideal, showing a small positive enthalpy of mixing. The enthalpy of formation of LiCoO₂ from oxides (Li₂O, NiO and CoO) and oxygen at 298 K is −142.5±1.7 kJ/mol (from sodium molybdate calorimetry) or −140.2±2.3 kJ/mol (from lead borate calorimetry). That of LiNiO₂ is −56.2±1.5 kJ/mol (from sodium molybdate calorimetry) or −53.4±1.7 kJ/mol (from lead borate calorimetry). The cobalt compound is thus significantly more stable than its nickel analogue. The phase assemblage LiCoO₂, Li₂O and CoO is seen at a lower oxygen pressure at constant temperature than the assemblage Co₃O₄/CoO, reflecting the stabilization of Co(III) in the ternary Li–Co–O system.     

Structure and magnetic properties of the intermetallic La2Co17−xMox (x=0.5, 1, 1.5, 2) and La2Co16−yFeyMo (y=0, 1, 2, 3, 4, 6) compounds

The effect of Mo and Fe atoms on the crystal structure and magnetic properties of the intermetallic La₂Co_17−xMo_x (x=0.5, 1, 1.5, 2), and La₂Co_16−yFe_yMo (y=0, 1, 2, 3, 4, 6) compounds have been studied by X-ray diffractometry, magnetic measurements and Mössbauer spectroscopy. All samples belong to the rhombohedral Th₂Zn₁₇-type structure and their lattice parameters a and c increase both with Mo and Fe content. From the La–Co–Mo samples only the one with x=0.5 presents planar anisotropy, whereas from the La–Co–Fe–Mo samples only the y=1 has uniaxial anisotropy. The magnetization M_S and the Curie temperature T_C decrease upon Mo substitution, whereas the anisotropy field H_A does not change significantly. In the Fe-substituted compounds M_S increases, but the Curie temperature increases slightly for 0⩽y⩽4 but decreases in y=6. The low temperature M–T curve shows that the samples La₂Co_16.5Mo_0.5, and La₂Co₁₀Fe₆Mo present a spin reorientation transitions at 70 and 260 K, respectively. Mössbauer samples were obtained for all Fe-containing samples in the temperature range 20–300 K. Above 260 K a jump in the values of the hyperfine fields and quadrupole splitting parameters is observed which can be associated to the spin reorientation.     

The characteristics of doubly and triply charged ions C2^2＋, C2^2- and C2^3＋

Based on group theory and atomic and molecular reaction statics, this paper derives the possible electronic states of C^{2+}_2, C^{2-}_2 and C^{3+}_2, and their reasonable dissociation limits and determines their ground electronic states C^{2+}_2(X^3Π_u), C^{2-}_2(X^1Σ^+_g) and C^{3+}_2(X^4Σ^-_u) using quantum mechanical calculations at the level of QCISD/6-311G^*. All the potential energy curves of their ground states have both a minimum and a maximum, which are the so-called "energy trapped" molecules. This sort of potential maximum is chiefly due to Coulomb repulsion. We propose the perturbation effect of ionic charges, which is used to explain why the orbital degeneracy of diatomic ions may be removed. The characteristics of potential curves for diatomic ions are briefly described.     

Structural, spectroscopic and crystal field analyses of Ni2+ and?Co2+ doped Zn2SiO4 powders

In this paper we presented structural and spectroscopic study of zinc silicate powder samples doped with divalent nickel and cobalt ions. Results of the Rietveld structural refinement, combined with optical spectroscopic study and theoretical crystal field calculations, are presented and discussed. X-ray diffraction studies were performed to establish reliable structure of the doped samples; in this way the interionic distances and chemical bond angles in Zn₂SiO₄:Co²⁺ and Zn₂SiO₄:Ni²⁺ were calculated and are reported for the first time. The room temperature reflection spectra of the prepared samples were measured in a spectral region from 4000 to 50000 cm^?1. The exchange charge model of crystal field has been applied to analyze the experimental spectra and assign all observed details in the spectra to the corresponding electronic transitions between the Co²⁺ and Ni²⁺ crystal field energy levels. The only input information for the model calculation was the experimentally obtained structural data, which were used for the calculations of the crystal field parameters with subsequent diagonalization of the crystal field Hamiltonian for both ions. Agreement between the calculated and experimentally detected energy levels of impurity ions was good. On the basis of the crystallographic and crystal field studies it was established that there exists a systematic trend of preferential occupation of one out of two possible crystallographic sites (namely, Zn2) for both impurity ions.     

Magnetic circular dichroism and absorption spectra of d° tetrahedral oxyanions and thioanions: MoS4 2-, MoO4 2-, WS4 2-, ReS4 -, VS4 3-, VO4 3- and OsO4

Absorption and magnetic circular dichroism spectra have been measured for the tetrahedral d° ions MoS₄ ^2-, MoO₄ ^2-, WS₄ ^2-, ReS₄ ^-, VS₄ ^3-, VO₄ ^3- and OsO₄ in the visible and ultra-violet spectral range. Comparison of the experimentally obtained MCD parameters with regard to their relative signs leads to the conclusion that probably the first two allowed longest wavelength electronic transitions of all these species have the same assignment (i.e., t ₁ →2e and 3t ₂ →2e, which seems likely on energetic grounds). An estimation of the MCD parameters by using eigenvectors from recently published molecular orbital treatments gave contradictory results.     

Characterization of K2CO3/Co–MoS2 catalyst by XRD,XPS, SEM,and EDS

MoS₂, Co–MoS₂ and K₂CO₃/Co–MoS₂ catalysts have been characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD analysis indicates that Co–MoS₂ is a primary phase in K₂CO₃/Co–MoS₂ catalyst and the diffraction lines of Co–MoS₂ are not changed by the addition of K₂CO₃. Co₉S₈ phase is not present at Co/Mo mole ratio of 0.5 using a co-precipitation method for preparation of cobalt–molybdenum catalyst. The binding energies (BEs) of chemical species present on the surface of the catalysts are compared through the course of catalyst preparation. K₂CO₃/Co–MoS₂ catalyst has been investigated as a function of dispersion of K on the surface and exposure to a mixture of carbon monoxide and hydrogen (syngas) by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The distribution of potassium on the surface of the K-promoted catalyst is not uniform.     

Dielectric, magnetoelectric, structure, and dissipative properties and the Mössbauer effect in PbFe1/2Nb1/2O3 ceramics in wide frequency and temperature ranges

High-quality fine-grained ceramic samples of classical multiferroics PbFe_1/2Nb_1/2O₃ (PFN) were synthesized. Their dielectric, magnetoelectric, and magnetic characteristics, including the Mössbauer effect, were measured over wide ranges of temperatures (10–1000 K) and field frequencies (from 25 Hz to 1 MHz). The temperature dependence of the dielectric loss exhibits a maximum between 150 and 170 K, likely due to magnetic ordering. The dependence of ? on the magnetic field displays an anomalous increase near the Curie temperature (370 K) that rises to 40% upon heating.     

Realisations of quantum GL p,q(2) and Jordanian GLh,h′(2)

The quantum group GL _p,q(2) is known to be related to the Jordanian GL_h,h(2) via a contraction procedure. It can also be realised using the generators of the Hopf algebra G _r,s. We contract the G _r,s quantum group to obtain its Jordanian analogue G _m,k, which provides a realisation of GL_h,h(2) in a manner similar to the q-deformed case.     

First-principles studies of electronic,optical,and mechanical properties of γ-Bi_2Sn_2O_7

The detailed theoretical studies of electronic,optical,and mechanical properties of γ-Bi_2Sn_2O_7 are carried out by using first-principle density functional theory calculations.Our calculated results indicate that γ-Bi_2Sn_2O_7 is the p-type semiconductor with an indirect band gap of about 2.72 e V.The flat electronic bands close to the valence band maximum are mainly composed of Bi-6s and O-2p states and play a key role in determining the electrical properties of γ-Bi_2Sn_2O_7.The calculated complex dielectric function and macroscopic optical constants including refractive index,extinction coefficient,absorption coefficients,reflectivity,and electron energy-loss function show that γ-Bi_2Sn_2O_7 is an excellent light absorbing material.The analysis on mechanical properties shows that γ-Bi_2Sn_2O_7 is mechanically stable and highly isotropic.     

Synthesis, Photo-physical and DFT Studies of ESIPT Inspired Novel 2-(2′,4′-Dihydroxyphenyl) Benzimidazole, Benzoxazole and Benzothiazole

Novel ESIPT inspired benzimidazole, benzoxazole and benzothiazole were synthesized from 2,4-dihydroxy benzoic acid and 1,2-phenelenediamine, 2-aminophenol, and 2-aminothiophenol respectively. The synthesized 2-(2′,4′-dihydroxyphenyl) benzimidazole, benzoxazole and benzothiazole are fluorescent and the emission characteristic are very sensitive to the micro-environment. They show a single absorption and dual emission with large Stokes shift originating from excited state intramolecular proton transfer. The absorption-emission characteristics of all these compounds are studied as a function of pH. The change in the electronic transition, energy levels, and orbital diagrams of synthesized compounds were investigated by the molecular orbital calculation and were correlated with the experimental spectral emission. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)].

Superconductivity,magnetism and crystal chemistry of Ba1−xKxFe2As2

BaFe₂As₂ is the parent compound of the ‘122’ iron arsenide superconductors and crystallizes with the tetragonal ThCr₂Si₂-type structure, space group I4/mmm. A spin-density-wave transition at 140 K is accompanied by a symmetry reduction to space group Fmmm and simultaneously by antiferromagnetic ordering. Hole-doping induces superconductivity in Ba_1?xK_xFe₂As₂ with a maximum T_c of 38 K at x ≈ 0.4. The upper critical fields approach 75 T with rather small anisotropy of H_c2. At low potassium concentrations (x ? 0.2), superconductivity apparently co-exists with the orthorhombically distorted and magnetically ordered phase. At doping levels x ? 0.3, the structural distortion and antiferromagnetic ordering is completely suppressed and the T_c is maximized. No magnetically ordered domains could be detected in optimally doped Ba_1?xK_xFe₂As₂ (x ? 0.3) by ⁵⁷Fe Mössbauer spectroscopy in contrast μSR results obtained with single crystals. The magnetic hyperfine interactions investigated by ⁵⁷Fe Mössbauer spectroscopy are discussed and compared to the ZrCuSiAs-type materials.     

Self-, N2-, O2-broadening coefficients and line parameters of HFC-32 for ν7 band and ground state transitions from infrared and microwave spectroscopy

Hydrofluorocarbons have been used as replacement gases of chlorofluorocarbons, since the latter have been phased out by the Montreal Protocol due to their environmental hazardous ozone-depleting effects. This is also the case of difluoromethane (CH₂F₂, HFC-32), which nowadays is widely used in refrigerant mixtures together with CF₃CH₃, CF₃CH₂F, and CF₃CHF₂. Due to its commercial use, in the last years, the atmospheric concentration of HFC-32 has increased significantly. However, this molecule presents strong absorptions within the 8–12 μm atmospheric window, and hence it is a greenhouse gas which contributes to global warming. Although over the years several experimental and theoretical investigations dealt with the spectroscopic properties of CH₂F₂, up to now pressure broadening coefficients have never been determined. In the present work, the line-by-line parameters of CH₂F₂ are retrieved for either ground state or ν₇ band transitions by means of microwave (MW) and infrared (IR) absorption spectroscopy, respectively. In particular, laboratory experiments are carried out on 9 pure rotational transitions of the ground state and 26 ro-vibrational transitions belonging to the ν₇ band lying around 8.2 μm within the atmospheric region. Measurements are carried out at room temperature on self-perturbed CH₂F₂ as well as on CH₂F₂ perturbed by N₂ and O₂. The line shape analysis leads to the first determination of self-, N₂-, O₂-, and air-broadening coefficients, and also of line intensities (IR). Upon comparison, broadening coefficients of ground state transitions are larger than those of the ν₇ band, and no clear dependence on the rotational quantum numbers can be reported. The obtained results represent basic information for the atmospheric modelling of this compound as well as for remote sensing applications.     

Asymptotic Stability, Concentration, and Oscillation in Harmonic Map Heat-Flow, Landau-Lifshitz, and Schrödinger Maps on {\mathbb R^2}

We consider the Landau-Lifshitz equations of ferromagnetism (including the harmonic map heat-flow and Schrödinger flow as special cases) for degree m equivariant maps from ${\mathbb {R}^2}We consider the Landau-Lifshitz equations of ferromagnetism (including the harmonic map heat-flow and Schr?dinger flow as special cases) for degree m equivariant maps from \mathbb R²{\mathbb {R}^2} to \mathbb S²{\mathbb {S}^2} . If m ≥ 3, we prove that near-minimal energy solutions converge to a harmonic map as t → ∞ (asymptotic stability), extending previous work (Gustafson et al., Duke Math J 145(3), 537–583, 2008) down to degree m = 3. Due to slow spatial decay of the harmonic map components, a new approach is needed for m = 3, involving (among other tools) a “normal form” for the parameter dynamics, and the 2D radial double-endpoint Strichartz estimate for Schr?dinger operators with sufficiently repulsive potentials (which may be of some independent interest). When m = 2 this asymptotic stability may fail: in the case of heat-flow with a further symmetry restriction, we show that more exotic asymptotics are possible, including infinite-time concentration (blow-up), and even “eternal oscillation”.