Quantum chemical calculations of the isomer shift in iron(II) complexes of 1,2,4-triazoles with a 1 A 1 ⇔ 5 T 2 spin transition

DFT calculations have been performed to determine the isomer shift for a series of iron(II) clusters with nitrogen-containing ligands which serve as models of coordination units in Fe(II) complexes with 1,2,4-triazoles possessing a ¹ A ₁ ? ⁵ T ₂ spin transition. Good agreement has been found between the theoretical and experimental values of the isomer shift for both low-and high-spin phases. Our calculations confirmed the hypothesis about relationship between the experimentally observed differences in the isomer shift for the low-spin phases of the complexes and variations of the Fe-N mean bond length.     

Water-methanol-benzene ternary system. Thermochemical experiment and computer simulation

Solution heats have been measured for benzene dissolved in mixtures of water with methanol at 25°C. The resulting values are compared with data for water-methanol-aniline, water-acetonitrile-benzene, and water-acetonitrile-aniline systems. Computer simulations have been performed for binary mixtures of water with methanol and dilute solutions of benzene in these mixtures. Thermodynamic and structural characteristics of solutions were obtained by calculations. The enthalpy of benzene transfer from water into a mixed solvent correlates with the relative deviation of the local composition from the mean composition of the mixture.     

Excitation of a cylindrical cavity by a helical current and an axial electron beam current

The explicit expressions (in the Vainshtein and Markov forms) are derived for the excitation of a cylindrical cavity with perfectly conducting walls and with impedance end faces. Excitation of a cylindrical cavity and a cylindrical waveguide with a preset nonuniform axial electron-beam current and a helical current with a variable pitch, which is excited by a concentrated voltage source and is loaded by a preset pointlike matched load, is considered. For the helical current, the integro-differential equation is formulated. The traveling-wave tube (TWT) is simulated in the preset beam current approximation taking into account the nonuniform winding of the spiral coil, nonuniform electron beam, and losses.     

Molecular dynamics simulation of the kinetics of nucleation of supercooled NaCl melt clusters

Approaches to describing the structure of metastable liquids are considered. A criterion for the classification of particles in a supercooled NaCl melt is suggested. The criterion is based on the Q₆ method and structural features of salt crystals. It was applied to analyze the configurations of clusters calculated by the molecular dynamics method. The results were interpreted using classic nucleation theory and the probabilistic approach. It was shown that crystalline phase nuclei with subcritical sizes existed in a metastable liquid. The evolution of nucleus sizes follows a complex mechanism. Along with monomer attachment and detachment reactions, collective structural fluctuations play a noticeable role.     

Kinetics and products of the catalytic oxidation of acetamidotoluenes with ozone in acetic acid

The kinetics of acetamidotoluene oxidation in glacial acetic acid in the presence of cobalt acetate is reported. At 95°C and atmospheric pressure, acetamidotoluenes are oxidized by molecular oxygen very slowly: oxidation is complete in 10–12 h, and the major reaction products are acetamidobenzoic acids (27–36% yield). The introduction of ozone into the reactive gas increases the reaction rate by one order of magnitude. The main role of ozone is to generate the active form of the catalyst.     

X-ray diffractometry diagnosis of laser diffusion of aluminum into silicon

High-resolution X-ray diffractometry was used to study alterations of the structure of single-crystal silicon taking place in the process of nonequilibrium solid-state diffusion of aluminum atoms occurring under heating of the near-surface layer by radiation of a CO₂ laser with pulse durations 1, 2, and 3 s. Crystal lattice deformation profiles, diffusion lengths, and densities of dislocation loops have been determined.     

Crystal structure and quantum chemical investigation of 4-(3,4-dichlorphenyl)-1,2,4-triazole

1,2,4-Triazole derivative substituted in the 4th position — 4-(3,4-dichlorphenyl)-1,2,4-tirazole — has been synthesized. Crystal and molecular structure of the compound were determined by single crystal X-ray diffraction. Molecular geometry optimization and effective charge calculations were performed by DFT methods.     

X-ray fluorescence determination of La,Ce, Pr,Nd, and Sm in industrial sediments of calcium sulfate using linear regression analysis

Industrial sediments of calcium sulfate semihydrate obtained from industrial extraction phosphoric acid and containing 0.3–4.5 wt % of impurity La?Sm are investigated by energy-dispersive X-ray fluorescence analysis (XRFA) and a procedure for the quantitative determination of cerium lanthanides in the sediments is developed. The use of linear regression analysis of X-ray fluorescence spectra of multielement industrial samples and models of individual compounds NaLn(SO₄)₂ · H₂O (cp grade) allowed us to resolve overlaps of spectral L-series lines for La–Sm, eliminate the background, and perform the regression assessment of line intensities of these elements. On this basis, we developed a procedure for the determination of La, Ce, Pr, Nd, and Sm in CaSO₄ · 0.5H₂O sediments with limits of detection (wt %): 0.022, 0.013, 0.011, 0.008, and 0.008, respectively. In concentration ranges (wt %) La (0.05–0.99), Ce (0.1–4.9), Pr (0.005–0.49), Nd (0.02–0.99), and Sm (0.005-0.19), the relative standard deviation RSD (n = 10, P = 0.95) was 18?27, 9?18, 20?31, 17?26, and 19?31%, respectively. A comparison of the results of XRFA with the data of inductively coupled plasma mass spectrometry confirms the accuracy of the results obtained according to OST (Branch Standard) 41-08-221-04.     

Isolation of Rare-Earth Elements from Mixtures of Calcium and Lanthanide Oxalates

The temperature regions for separate crystallization of rare-earth element (REE) oxides of the cerium group in the presence of CaCO₃ have been determined using X-ray diffraction, differential thermogravimetric analysis, inductively coupled plasma mass spectroscopy, and X-ray fluorescence. The possibility to separate REE oxides from CaCO₃ in H₂SO₄ solutions after heat treatment (450–600°C) has been studied. The solid phase of the precipitate is represented by slightly soluble calcium sulfate, whereas the REE oxides pass into the liquid phase in the form of highly soluble sulfates. After heat treatment of the test mixture of REE oxalates and calcium oxalate at a temperature higher than 750°C, calcium compounds pass into 1–2% HNO₃ liquid phase in the form of nitrates, whereas lanthanide oxides remain in the insoluble phase of REE oxide solid solution having CeO₂ structure.     

X-ray specular reflection under conditions of extremely asymmetric noncoplanar diffraction from a bicrystal

The angular dependence of the intensities of X-ray specular reflection has been rigorously analyzed under conditions of noncoplanar grazing Bragg diffraction in a crystal coated with a crystalline film (bicrystal). It is shown that the anomalous angular dependence of the specular-reflection intensity is extremely sensitive to the thickness (from fractions of a nanometer up to several nanometers), deformation, and the amorphization degree of the crystalline films. The optimum conditions for recording intensities are attained at grazing angles equal to 1.5–4.0 of the critical angle of the total external reflection.