Valence electronic structure of uranyl nitrate UO2(NO3)2·2H2O

Experimental and theoretical studies on the electronic structure of a uranyl nitrate hydrate, UO₂(NO₃)₂·2H₂O, have been performed by X-ray photoelectron spectroscopy (XPS) and with relativistic DV-Xα molecular orbital methods. The XPS spectra are measured within five minutes of X-ray irradiation, which causes negligible damage to the sample. Taking into consideration the calculated results, each peak of the experimental spectrum is assigned. The theoretical spectrum of the uranyl nitrate is in good agreement with the present experimental spectrum.     

The band electronic structures of (BEDTTTF)2X,X− = BrO4− and ReO4−

The strictly isostructural organic metals, (BEDTTTF)₂ReO₄ and (BEDTTTF)₂BrO₄ consist of sheets of BEDT-TTF (abbreviated ET) donor molecules which form a novel two-dimensional network. Despite the similar structures these salts possess different physical properties. (ET)₂ReO₄ is a highly anisotropic metal down to 80 K but becomes insulating below this temperature. An applied pressure greater than 4.5 kbar reportedly suppresses the MI transition and gives superconductivity at 2 K. However, no superconductivity has yet been observed for (ET)₂BrO₄. Band electronic structure calculations derived from their ET molecule network geometries at 298 and 120 K, and intrastack and interstack energies between nearest neighbor ET molecules, show that (ET)₂ReO₄ and (ET)₂BrO₄ are highly anisotropic metals, and both possess very similar band structures.     

Experimental and theoretical study of the ν(HF) absorption band structure in the H2O…HF complex

The νHF absorption band shape of the H₂O…HF complex is studied in the gas phase at a temperature of 293 K. The spectra of H₂O/HF gaseous mixtures in the range 4000–3400 cm^?1 are recorded at a resolution of 0.2–0.02 cm^?1 with Bruker IFS-113v and Bruker IFS-120 HR vacuum Fourier spectrometers in a 20-cm cell. The spectra of the H₂O…HF complex in the region of the ν₁(HF) absorption band are obtained by subtracting the calculated spectra of free H₂O and HF molecules from the experimental spectrum. The ν₁ band of the H₂O…HF complex has an asymmetric shape with a low-frequency head, an extended high-frequency wing, and a characteristic vibrational structure. Two approaches are used to calculate the ν1 band shape as a superposition of rovibrational bands of the fundamental and hot transitions involving the low-frequency modes of the complex. The first approach is based on a simplified semiempirical procedure. The second approach relies on a nonempirical anharmonic calculation of the vibrational energy levels, the frequencies and intensities of the corresponding transitions, and the rotational constants. These parameters are obtained by calculating ab initio the potential energy and dipole moment surfaces in the second-order Möller-Plesset approximation and using the variational method to solve one-, two-, and three-dimensional anharmonic vibrational problems. The absorption spectrum of the complex in the range 3600–3720 cm^?1, reconstructed using the nonempirical electro-optical parameters, reproduces rather well the main features of the experimental spectrum, including the relative intensities of peaks of the vibrational structure. However, the interpretation of most of the structural features of the spectrum differs from that adopted in the semiempirical scheme. First of all, it follows from the results of nonempirical calculation that the central, most intense, maximum of the experimental spectrum should correspond to the v ₁=1←0 transition from the ground vibrational state. This fact gives rise to a new value of the vibrational transition frequency ν ₁ ⁰ in the H₂O…HF complex equal to 3635 cm^?1, which is higher than the commonly accepted value of 3608 cm^?1.     

Synthesis and sonocatalytic property of rod-shape Sr(OH)2·8H2O

A novel rod-shape sonocatalyst Sr(OH)₂·8H₂O was prepared by a facile precipitation method, and characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and UV–vis absorption spectroscopy. Comparative sonocatalytic degradation experiments were carried out in different conditions under ultrasonic irradiation by using rhodamine B (RhB) as the model substrate, indicating that Sr(OH)₂·8H₂O was highly sonocatalytic. Total organic carbon experiment demonstrated Sr(OH)₂·8H₂O with mass mineralization of organic carbon. The effects of catalyst amount, initial RhB concentration and ultrasonic energy of degradation were investigated, and the sonocatalyst could be reused 5 times without significant loss of activity. Furthermore, the potent degrading capability was ascribed to ultrasonic cavitation producing flash light/energy which generated radicals (e.g., OH) with high oxidation activity.     

Study of the structure of FeSiF6·6H2O by EPR and optical spectra

The method for determining the crystalline structure from relevant EPR zero-field splitting and optical spectra data is applied to ferrous fluosilicate (FeSiF₆·6H₂O. The results, consistent with data from Mossbauer and IR magnetic resonance, show that the effective symmetry of the Fe₂₊ site in FeSiF₆·6H₂O is a rhombic distortion rather than a trigonal one (D_3d).     

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^?1 and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.     

Influence of atmospheric humidity on the symmetry and phase transitions of layered potassium oxyfluorides K2NbOF5 · H2O

Crystals of K₂NbOF₅ · H₂O have been grown, polarization optical investigations have been performed, and the birefringence and rotation angle of the optical indicatrix have been measured in the temperature range 100–400 K. It has been found that, depending on the degree of atmospheric humidity, the layered K₂NbOF₅ · H₂O crystal at room temperature can be in three states, namely, A, B, and C, which differ in symmetry and properties of the crystal. The K₂NbOF₅ · H₂O crystal in the A state exists at a relative humidity RH = 90–100% and undergoes a first-order improper ferroelastic phase transition P $\bar 1$ ? C2/m, which is accompanied by strong anomalies of the optical characteristics, twinning, and shear strain x ₆ at temperatures T ₂ ^↓ = 308 K and T ₂ ^↑ = 313 K. The most stable state of the K₂NbOF₅ sdH₂O crystal is the B state (RH = 20–90%), which retains the monoclinic symmetry C2/m in the temperature range 100–370 K. In a dry atmosphere (RH = 0–20%) or at T ₁ ≈ 370 K, the crystal becomes anhydrous (K₂NbOF₅) with the symmetry P4/nmm (the C state). The difference between the crystals in the states A and B is explained by the presence or absence of water molecules in interlayer spaces.     

Defects,phase transitions and dynamical disorder in superionic protonic conductors H3OUO2PO4 · 3H2O and CsHSO4

Specific properties of the hydrogen bond and protons appear to be responsible for the formation of the quasi-liquid state of conducting ions and the resulting superionic behaviour. This state is reached by successive phase transitions involving the mobile species and their interactions with a more or less rigid framework. H₃OUO₂PO₄ · 3H₂O (HUP) and CsHSO₄ can be considered as models of wet and dry superionic conduction, respectively. Interactions between static effects and dynamical disorder as well as the coupling between sublattices are discussed in relation to results obtained by calorimetry, impedance spectroscopy (up to 10 GHz), vibrational spectroscopy and quasi-elastic neutron scattering.     

A new acentric borate of K2Ba[B4O5(OH)4]2·10H2O: synthesis,structure and nonlinear optical property

A new acentric mixed metal borate of composition K₂Ba[B₄O₅(OH)₄]₂·10H₂O, has been successfully obtained by slow evaporation solution method. The compound crystallizes in the Orthorhombic space group Pna21 (No.33) with a = 16.8668(7) Å, b = 13.0903(5) Å, c = 11.5529(5) Å and Z = 4. [B₄O₅(OH)₄]^2? clusters serve as fundamental building unit linking with BaO₈, K1O₆, K2O₇ by common O atoms to form three-dimensional layer structure. The second harmonic generation measurements in the powder samples reveal that the compound exhibits approximately 0.5 times that of KH₂PO₄ (KDP) and phase matching.     

Structure of the (0001) surface of α-Al2O3 from first principles calculations

Fully self-consistent ab initio calculations based on pseudopotentials are used to study the structure and energetics of the basal-plane surface of α-Al₂O₃. The calculated forces on the atoms are used to relax the atomic positions to equilibrium. It is shown that surface relaxations are very large and lead to a reduction of the surface energy by over a factor of two. The results support the validity of earlier work based on pair-interaction models.     

Potential energy surface for the hydroperoxy and water (HO2·H2O) radical complex

A potential energy surface for the system of a hydroperoxy radical and a water molecule is presented. The surface was sampled using constrained density functional theory optimizations performed at the B3LYP level of theory using a 6–311 ++G(3df,3pd) basis set. The data points were fitted to an analytical function based on a common 4-point model for water and a 5-point model for the peroxy radical. A weighted least-squares fit of the parameters was performed using the nearest neighbour pivot method.     

Crystal structure of the inverse weberite ZnFeF5(H2O)2, magnetic and mössbauer study of the antiferromagnet ZnFeF5(H2O)2 and ferrimagnet Mn FeF5(H2O)2

The room temperature crystal structure of the inverse weberite ZnFeF₅ (H₂O)₂ is refined from powder X-ray diffraction. The cell is orthorhombic (S.G. Imma, a = 7.475(1) →A, b = 10.766(1) →A, c = 6.594(1) →A, z = 4). Below T_N = 9(2) K, ZnFeF₅(H₂O)₂ becomes a 1-D antiferromagnet. This behaviour was characterized by susceptibility and magnetization measurements and Mössbauer spectroscopy. On the contrary, isotypic MnFeF₅(H₂O)₂ is confrimed to be a ferrimagnet below T_c = 39.5(1)K. Its magnetic and Mössbauer characteristics are, above and below T_c,and agree with a 3-D magnetic character. Ferrimagnetism could be due to frustration effects as in previously described Fe₂F₅(H₂O)₂.     

First-principles calculations of 5d atoms doped hexagonal-AlN sheets：Geometry,magnetic property and the influence of symmetry and symmetry-breaking on the electronic structure

The geometry, electronic structure and magnetic property of the hexagonal AlN(h-AlN) sheet doped by 5d atoms(Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3v and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μBfor Lu, Ta and Ir; 1μB for Hf, W, Pt and Hg; 2μB for Re and Au; and 3μB for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.     

Measurements and calculations of He-broadening and -shifting parameters of the water vapor transitions of the ν 1 + ν 2 + ν 3 band

The water vapor line broadening and shift in the ν ₁?+?ν ₂?+?ν ₃ band induced by helium pressure were measured using a Bruker IFS 125HR FTIR spectrometer. The measurements were performed at room temperature at a spectral resolution of 0.01?cm^?1 and in a wide He pressure range. The shifting coefficients δ are mainly positive, in contrast to the line center shift induced by other mono-atomic gases. Calculations of the coefficients γ and δ were performed in the framework of the semi-classical method. The influence of the rotational dependence of the isotropic intermolecular potential and accidental resonances in the H₂O molecule on the shifting coefficients is discussed. Calculated values of line profile parameters are in a good agreement with observed parameters.     

Line positions and intensities in the υ2 band of H216O

The constants involved in the rotational expansion of the transformed transition moment operator of the v ₂ band of H₂ ¹⁶O have been determined through a fit of about 110 measured line intensities. A comparison between theoretical and experimental values of these constants is given. The coefficient ²μ _x of the expansion of the dipole moment with respect to normal coordinates is deduced to be

Moreover, a knowledge of the transformed transition moment operator has been used to compute the whole spectrum of the v ₂ band.     

Low-temperature phase transitions and dynamics of ammonium in (NH4)3H(SO4)2 and [(NH4)1−x Rbx]3H(SO4)2 crystals

The (NH₄)₃H(SO₄)₂ and [(NH₄)_0.82Rb_0.18]₃H(SO₄)₂ crystals are investigated by dielectric spectroscopy, inelastic incoherent neutron scattering (IINS), and neutron powder diffraction. A comparative analysis of the data obtained is given. It is shown that the phase transitions II ? III, III ? IV, IV ? V, and V ? VII in the (NH₄)₃H(SO₄)₂ crystal are accompanied by changes in the orientation ordering of the NH ₄ ⁺ ions. In the [(NH₄)_0.82Rb_0.18]₃H(SO₄)₂ crystal, these phase transitions are completely suppressed and the long-range order inherent in the II phase is retained over the entire temperature range covered (6–300 K). It is revealed that this crystal at the temperature T _g≈70 K undergoes a transition to the dipole glass phase, which is attended by “freezing” the orientation disordering of the ammonium ions.     

First principles calculations of the structural and electronic properties of(CdSe)n clusters

The structural and electronic properties of (CdSe)n(1≤n≤5) clusters are calculated using density functional theory within the pseudopotential and generalized gradient approximations. The calculated binding energies and highest occupied molecular orbital lowest unoccupied molecular orbital gaps are compared with those obtained within local density approximation.     

Correlation of dielectric properties,Raman spectra and calorimetric measurements of β-cyclodextrin-polyiodide complexes (β-cyclodextrin)2 ·BaI7 ·11H2O and (β-cyclodextrin)2 ·CdI7·15H2O

The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)₂·BaI₇·11H₂O and (β-CD)₂·CdI₇·15H₂O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba²⁺ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm^?1, 170?cm^?1 and 165–166?cm^?1 are due to the charge transfer interactions in the polyiodide chains.     

The crystal structure of tetrammine copper sulphate Cu(NH3)4SO4·H2O

The crystal structure of tetrammine copper sulphate was determined. The orthorhombic unit cell with dimensions a=12.12, b=10.66, c==7.07 Åcontains four molecules of Cu(NH ₃)₄ SO ₄.H ₂ O, the space group is Pbnm (D _2h ¹⁶ ).The atomic coordinates were determined from the projections of the Patterson function and the electron density onto the (001) and (010) planes. The complex cation Cu(NH ₃)₄ ⁺⁺ is approximately planar, the groups of NH ₃ are linked by co-valent bonds to the central Cu atom. The average distance of the groups of NH ₃,which are approximately at the corners of a square surrounding the central Cu atom, is 2.90 Å, the distance Cu-NH ₃,corresponding to the co-valent bond, is 2.05 Å.