Calculation of the Tautomeric Properties of 3‐Formyl‐Tetrinic Acid by the ab initio and DFT Methods

We have carried out a nonempirical quantumchemical calculation with full optimization of the geometry of all theoretically possible tautomeric forms of 3formyltetrinic acid (FTRA) according to the Møller–Plesset secondorder perturbation theory with the use of a 6–31G(d) double zeta basis set. The correlation corrections to the total energy of molecules for optimized geometric configurations were calculated in the 631G(d,p) basis. All the possible tautomeric forms of FTRA and the harmonic vibrational frequencies were also calculated within the density functional theory (DFT) with the use of the Perdew–Burke–Ernzerhof (PBE) functional in a threeexponent basis. It is shown that FTRA in vapors (in the perfect gas approximation) exists in the form of a mixture of three enol forms, among which two exoforms predominate. The frequencies and forms of normal vibrations for each cisenol tautomer in the region of vibrations of ketogroups and double bonds differ widely, which permits identification of the tautomers present in the mixture. The possible mechanisms of enolenol transformations of 3acyltetrinic acids are discussed.     

Infrared Spectroscopic Study of N,N‐Dimethylthioformamide Complexes of the Hofmann Type

Four new Hofmanntype complexes, M(DMTF)₂Ni(CN)₄, (where DMTF is dimethylthioformamide, M=Mn, Cd, Co, or Ni) were synthesized and their structure was determined by an elemental analysis and infrared spectroscopy. The IR spectra of DMTF and its nickel tetracyanine complexes with Mn(II), Cd(II), Co(II), and Ni(II) have been investigated within the range 4000–400 cm^–1. The frequency shifts in the metal complexes agree with the assignment of the CS and CN frequencies. The complexes consist of infinite planar polymer layers of |MNi(CN)₄|. Ndimethylthioformamide is coordinated to this layer from above and below; it is a monodentate ligand and is Sbonded through the metal atom in these complexes.     

Spectral‐Luminescence Characteristics of Polyphenyls and Polyacenes in the Gas Phase in Electron‐Beam Excitation

The spectra of electronenergy loss, excitation functions, and fluorescence spectra in excitation of the vapor of polyphenyls and polyacenes by electron beams of different energies are determined. The influence of successive complication of the molecules under study on these spectralluminescence characteristics is tracked. Unlike the optical absorption spectra, in the spectra of electronenergy loss of all the substances studied one observes a band which is related to the singlettriplet transition S ₀–T ₁. The transitions up to S ₀–S ₅ are recorded in excitation of the molecules by highenergy electrons, including the region of vacuum ultraviolet. From the functions of fluorescence excitation the authors have determined the excitation thresholds that correlate with the energies of the S ₁ levels, except for pyrene in which the S ₀–S ₁ transition is forbidden and does not show up not only in photon excitation but also in electronbeam excitation, although the intercombination forbiddenness in the latter case is removed and the S ₀–T ₁ band is observed.     

Updated Analysis of Gallium Chelate and Vanadium Chelate Solutions with 4‐(2‐Pyridylazo)Resorcinol and Xylenol Orange

The characteristic factors of the gallium and vanadium chelates with the ligands 4(2pyridylazo)resorcinol (PAR) and xylenol orange (XO) have been determined with the aid of the principle of correction, which makes it possible to eliminate the influence of the surplus ligand in the solution of its chelate with methane (which makes calculation easier) and thereby provides a more acceptable method in comparison with others. The real molar coefficients of extinction of the chelates Ga and V with PAR and XO have been determined and a detailed calculation of the stoichiometric ratios of chelates has been made. The results have shown that the chelates formed have the following structure: Ga(PAR), Ga(XO), V(PAR)₂, and V(XO).     

Spectral‐Luminescent Properties of Oxazoles and Oxadiazoles in a Gas Phase on Excitation by Electrons

The energyloss spectra of electrons, fluorescence excitation functions, and the fluorescence spectra on excitation of the vapors of a number of oxazoles and oxadiazoles by monokinetic beams of electrons of various energies are determined. In contrast to optical absorption spectra, in the energyloss spectra of a number of studied substances a band associated with the S ₀–T ₁ singlettriplet transition is observed. The –^*type transitions are fixed up to S ₀–S ₅ on excitation of molecules by highenergy electrons, including the region of vacuum ultraviolet. The cross sections of elastic and inelastic collisions of electrons of different energies with POPOP molecules have been measured. The dependences obtained differ substantially from those calculated in the Born approximation. The cross section of elastic scattering is in a rather good correspondence with the geometric section of the molecule.     

Spectral and Quantum‐Chemical Investigation of the Influence of the Spatial Structure of a Polymeric Complex on the Mechanism of Catalytic Oxidation of Sulfur Dioxide with Oxygen

Based on the calculations carried out by the ZINDO/S method, we suggest interpretation of the electronic absorption spectra of solvate complexes of cobalt with polyethyleneimine and sulfite ion. The quantumchemical analysis of the spectrophotometric data has shown that the change in a concentration of cobalt ions in a solution leads to conformation changes in a polymeric chain. The kinetic and quantumchemical investigation of the mechanism of catalytic oxidation of SO₃ ^2– to SO₄ ^2– is carried out. We suggest a spatial structure of the transient state that provides optimum conditions for the oxygenation reaction. The kinetic data indicate that the catalytic activity of cobalt ions fixed on a polymeric matrix is by three orders of magnitude higher than of their monomeric analogs. Using calculations performed by the RM3 method, we show that the oxygenation process is of exothermal nature and that there is a direct correlation between the reactionrate constant and the energy released in the process of oxygenation (E). On substituting ammonia molecules by a polyethyleneimine fragment, E increases by 39.39 kcal/mole.     

Determination of the Elemental Composition of Chalcogenide Powders by the X‐Ray Fluorescence Method

A procedure of xray spectral fluorescence analysis of the elemental composition of As _x S_100–x chalcogenide powder samples is developed and its metrological characteristics are established. In determining the content of the components in an As₅₀S₅₀ sample, the relative standard deviation was 0.0030 for As and 0.0035 for S. The results of the xray spectral fluorescence analysis are in good agreement with the data of a gravimetric method.     

Calculation of the Parameters of a One‐Coordinate Model of the VGaSAs and VGaSnGa Complexes in Gallium Arsenide

Experimental optical bands of the emitting complexes (a gallium vacancy with a donor at the nearest, from the vacancy, sublattice site) V_GaS_As and V_GaSn_Ga in GaAs are investigated in a wide temperature range. The parameters of a onecoordinate model of these centers are determined. A configurationcoordinate diagram of the V_GaS_As complex is constructed. Calculation of the field dependences of emission rates is carried out in terms of the parameters of the onecoordinate model of the V_GaS_As complex and the data obtained are compared with the results of experimental studies of the emission of electron holes from a deeplying center of the V_GaS_As complex.     

Equations for the Magnetization Modes in a System Having a Quadruple Nucleus with the Spin S = 1

Within the framework of the method of a density matrix, differential equations are obtained that describe the evolution of the modes of magnetization <Î₊>, <Î_{+ z} >, and <Î_{+ z} ²> for a spin system containing a nucleus with a 1/2 spin connected scalarly with the quadruple nucleus of the spin S = 1 in the presence of crosscorrelation between the dipole ISinteractions, anisotropy of the chemical shift of the I and S nuclei, and quadruple interaction of the S nucleus. The equations are used for analysis of the evolution of the intensities of each line in the triplet of the Raman spectrum of the 1/2 spin. Expressions for the times of crossrelaxation and the times of transverse relaxation of each of the lines of the triplet are obtained.     

A Cathodoluminescent Screen of Columnar Structure for Field Emission Displays

We have suggested and implemented a method of creation (growing) of sublimatescreens formed by singlecrystal luminophor columns which are perpendicular to an amorphous (e.g., glass) substrate. The diameters of the columns are 3–5 m, the height 7–10 m. The columnar singlecrystal structure of the screen ensures the high light yield and radiation color needed for field emission displays. It is possible to select the growing regime so that the columns are very closely spaced (1–2 m). The gaps can be filled with a conducting opaque material that increases the contrast of the screen and improves their electrical conductivity.     

Manifestation of Extracoordination in the Resonance Raman Spectra of Water‐Soluble Cation Co‐Porphyrins

Resonance Raman spectra (RRS) of Co(II) and Co(III)5,10,15,20tetrakis(4Nmethylpyridinium)porphyrin ((Co^II(TmpyP4), and Co^III(TMPyP4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies ₂, ₄, ₈, and ₆ — the markers of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For Co^III(TmpyP4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for Co^II(TmpyP4). The spectral effects observed are related to different electron influence of the extraligands on the system of the porphyrin ring. In the case of Co(III)porphyrin, interaction of the d orbitals of the metal and the e _g ^*orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)complex. For Co^III(TmpyP4), a linear correlation between the oscillation frequencies ₂, ₄, ₈, and ₆ and the experimental Gutmann parameters characterizing the electronacceptor properties of solvents is found.     

Gas‐Kinetic Temperature of Planar High‐Frequency Capacitive Discharge Plasma in N2/CO2/He Gas Mixtures

Using methods of emission spectroscopy, we have determined the gaskinetic temperature fields of planar highfrequency capacitive discharge plasma in N₂/CO₂/He gas mixtures depending on the excitation frequency, discharge current, pressure, and chemical composition of the mixture. It is shown that the dominant contribution to the neutral component heating in the center of the discharge chamber is made by the processes of V–T relaxation of vibrationally excited molecules N₂(X ¹, V) and CO₂(X ¹, V), whereas in the zones near the electrodes an important role in the heating is played, along with the V–T relaxation of the N₂(X ¹, V) and CO₂(X ¹, V) molecules, by the processes of deactivation of the metastable states A ³ of the N₂ molecule.     

Calculation of Out‐of‐Plane Vibrations of a Porphin Molecule

Using the DFT/B3LYP method with the base set 631G^**, we carried out calculation of the frequencies of the normal vibrations of porphin and of its five isotopic types. Scaling of force constants for outofplane vibrations has been performed in independent natural coordinates. The symmetry coordinates are introduced and a force field for outof plane vibrations of a porphin molecule in independent coordinates of symmetry is obtained. A new correlation of the frequencies of vibrations in the type of the symmetry B _1u for the isotopic type of the d ₂ porphin molecule is suggested on the basis of discrete analysis of the distribution of a potential energy.     

Absorption Spectra of Pentamers of Tetrapyrrole Compounds in Aqueous Solutions

Pentamers of two types have been obtained in aqueous solutions containing mixtures of two tetrapyrrole compounds, in whose molecules there are positively or negatively charged peripheral groups. The pentamers of one type include one molecule of mesotetra(4Nmethylpyridyl) porphin (TMPP) and four molecules of the complex of mesomono(nsulfophenyl)etioporphyrin II with palladium (PdSPhEP), and the pentamers of the other type include one molecule of sulfonated phthalocyanine (PCS) and four molecules of TMPP. The absorption bands of the pentamers are broadened and shifted toward longer wavelengths in comparison with the bands obtained as a result of the addition of the spectra of the monomers. It seems that the changes in the absorption spectra are first of all due to the change in the interaction of the molecules of the pigments with the molecules of the surrounding in formation of associates and due to the influence of the resonance dipoledipole interaction between the molecules in the associates. The influence of the intermolecular photoinduced charge transfer is also possible (it is most probable for the associates with PCS). We have revealed an effective quenching of the fluorescence of PCS and TMPP solutions upon heteroassociation.     

Calculation of Quantum‐Chemical Characteristics of the Ground and Excited Electronic States of Porphin and Its Tetrapyrrole Isomers

Using the CNDO/S method, we have performed quantumchemical calculations of the ground and excited electronic states of porphin molecules (symmetry D _2h ) and a number of porphin isomers: porphycene (C_2h ), hemiporphycene, corphycene (C_2v ), isoporphycene, and three nonsynthesized structural isomers of the porphin skeleton by its bridge groups —(CH) _meso —. The results of the calculations are compared with the corresponding data for the freebase porphin molecule (H₂P). Near the boundary between the occupied and vacant orbitals the isomers form rows of singleelectron levels with similar energy characteristics. For the MOs of these isomers, the H₂P MOs closest in distribution on the comparable atomic centers are given. The weak (Q) and strong (B) transitions in the visible and near UV regions point to the porphyrin type of spectra of all the isomers. The calculation data on the excited electronic states of N, g, and ntype H₂P near and above the B states are given; the presence of such states in other isomers is shown. The calculation does not point to a difference in the position of the first singlet transitions in the first five isomers. The calculation data on the lower singlettriplet transitions are also reported.     

Mössbauer effect and discovery of new hexagonal ferrites prepared at 980^\circ C

In the present article, undoped and Codoped Mtype Srhexaferrites have been prepared at low temperatures down to 980 C for the first time by the usual ceramic procedure and sintering technique. On these materials, a CoK Xray diffraction analysis and the room temperature ⁵⁷Fe Mössbauer spectroscopy (MES) were carefully performed. The results obtained are described and interpreted. The mechanism of Co substitution partially in place of iron and the site of its occupancy were proposed and established.     

Spectral‐Luminescent Properties of Certain Substituted Arylpolyenes and Their Features

We investigated fluorescence and fluorescence excitation spectra of five substituted diphenylpolyenes with the number of double bonds in the chain n = 2 or n = 3 and substituents NO₂, N(CH₃)₂, and NH₂ in different media (toluene and noctane) at low (77 and 4.2 K) temperatures. The duration of fluorescence () and the quantum yield of fluorescence () of the four compounds investigated were measured at room temperature. The influence of the electron donoracceptor interaction in one of the compounds on its spectralluminescent properties has been analyzed.     

Influence of Close‐Range Dipole‐Dipole Interactions on the Real Part of the Susceptibility of a Dense Resonance Medium

Based on a solution of the stationary modified Bloch equations, an investigation is made of the influence of the effect of internal optical bistability (IOB) on the behavior of the refractive index of a dense resonance medium as a function of the constant b of closerange dipoledipole interactions, frequency detuning, and the intensity of optical radiation. The conditions of existence of the IOB effect of the system dense resonance medium + optical radiation are found and the dynamics of the loop width of the hysteresis dependence of the population difference of the resonance levels of the medium on the characteristics of the system is traced. The domains of the parameters are determined in which the effects of selffocusing and selfdefocusing of the radiation propagating in a dense resonance medium can take place.     

Anti‐Stokes Luminescence of Cadmium Telluride Nanocrystals

For the first time, the antiStokes luminescence in colloidal solutions of CdTe nanocrystals on excitation below the absorption edge has been discovered. The maximum spectral shift to the shortwave region relative to the excitation energy E _con ^max = 319 meV is obtained for meansized nanocrystals (2.5 nm). The conversion efficiency of the absorbed radiant energy is 1.3·10^–2%. The rise in the antiStokes photoluminescence intensity with increasing temperature and the linear dependence on the exciting radiation intensity have been established. It is shown that the effect observed cannot be caused by twophoton excitation or by Auger recombination. It is assumed that the basic mechanism of the luminescence observed is the radiative recombination through the energy levels of the states attributable to the disturbance of the crystal structure in the nanocrystals.     

Absorption Spectra and Thermostimulated Luminescence of Irradiated KBr Crystals with a High Content of an Na Impurity

The influence of high concentrations of the Na⁺ impurity on the photo and thermostimulated luminescence in an xirradiated KBr crystal has been studied. It is revealed that at an impurity concentration of 1 mol.% the absorption spectrum of the KBr:Na crystal possesses only the bands belonging to the (, I _A) and (F, H _A) pairs of the centers and that the thermoluminescence spectrum consists of two peaks with a maximum at 140 and 165 K.