Theoretical interpretation of spin-polarized X-ray absorption spectra of Mn in MnP

On the basis of the multiple scattering approach in combination with the spin-polarized self-consistent potential calculation, an interpretation is proposed for the spin-polarized x-ray absorption spectra near the Mn K edge in MnP. The effect of the core vacancy potential on the spectra is analyzed and found to be insignificant. The method used for the calculations allowed the separation of the effect of the dipole transition matrix element on the spectra and the effect of the density of unoccupied electron states. It is shown that the transition matrix element causes an intensity redistribution only near the absorption jump, while the difference in the densities of states is most pronounced in the energy region 35–55 eV away from the main edge and leads to a shift in energy for the spectra corresponding to the two spin directions. The effect of the spin-dependent broadening caused by the dependence of the mean free path (as a function of energy) on the photoelectron spin is studied. It is shown that this factor considerably affects only the intensities of the peaks in the energy region lying within less than 12 eV from the main edge.     

Combined digital filtering of harmonic content of phase-shift keyed signals in the problem of estimation of the time delay

We propose a two-step method for digital filtering of phase-shift keyed signals filtering in the problem of determination of the time delay during the multichannel propagation. The first step is realized as an information-optimal linear filter with complex coefficients, while the second step, as a quadratic filter based on the minimum-variance criterion. The e.ciency of the proposed method is demonstrated for short PSK signals with various carrier frequencies against the background of additive and multiplicative noise. The developed algorithm can easily be implemented in real time on the basis of a digital signal processor. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 3, pp. 255–264, March 2007.     

Excitation efficiency of working transitions in copper-vapor lasers

The conditions under which the influence of the discharge circuitry inductance on the efficiency of pulsed-periodic copper-vapor lasers is weak are determined. It is shown that for efficient pumping of the lasing transitions of Cu atom in these lasers it is advisable to form an excitation pulse having steep edges of the voltage applied to the discharge tube with the duration spanning the pumping period and termination of the lasing process providing, at the same time, the conditions for aperiodic behavior of the discharge during the excitation pulse. Such a pumping pulse can be formed due to a partial discharge of the storage capacitor in the laser discharge circuit. It is also shown that under such conditions of excitation the efficiency of copper-vapor laser (CVL) with respect to the energy pumped into the active element can reach 10%.     

Understanding the electronic structure of 4d metal complexes: from molecular spinors to L-edge spectra of a di-Ru catalyst

L(2,3)-edge X-ray absorption spectroscopy (XAS) has demonstrated unique capabilities for the analysis of the electronic structure of di-Ru complexes such as the blue dimer cis,cis-[Ru(III)(2)O(H(2)O)(2)(bpy)(4)](4+) water oxidation catalyst. Spectra of the blue dimer and the monomeric [Ru(NH(3))(6)](3+) model complex show considerably different splitting of the Ru L(2,3) absorption edge, which reflects changes in the relative energies of the Ru 4d orbitals caused by hybridization with a bridging ligand and spin-orbit coupling effects. To aid the interpretation of spectroscopic data, we developed a new approach, which computes L(2,3)-edges XAS spectra as dipole transitions between molecular spinors of 4d transition metal complexes. This allows for careful inclusion of the spin-orbit coupling effects and the hybridization of the Ru 4d and ligand orbitals. The obtained theoretical Ru L(2,3)-edge spectra are in close agreement with experiment. Critically, existing single-electron methods (FEFF, FDMNES) broadly used to simulate XAS could not reproduce the experimental Ru L-edge spectra for the [Ru(NH(3))(6)](3+) model complex nor for the blue dimer, while charge transfer multiplet (CTM) calculations were not applicable due to the complexity and low symmetry of the blue dimer water oxidation catalyst. We demonstrated that L-edge spectroscopy is informative for analysis of bridging metal complexes. The developed computational approach enhances L-edge spectroscopy as a tool for analysis of the electronic structures of complexes, materials, catalysts, and reactive intermediates with 4d transition metals.     

Conformational characteristics of polycaproamide in dimethylacetamide containing lithium chloride

The viscosity behavior, index of refraction, and density of dilute polycaproamide solutions in DMAc containing lithium chloride have been studied. On the basis of temperature dependences of the index of refraction and the density of solutions, the θ-condition of polycaproamide solutions in DMAc containing 2.5% lithium chloride is estimated as 21.3°C. From intrinsic viscosity [η] measurements, the coefficients of swelling of a polymer coil, the mean-square distance between chain ends, and other parameters of macromolecules in solution are calculated.     

Local atomic and electronic structure of quantum dots based on Mn- and Co-doped ZnS

Solid solutions of zinc sulfide with manganese and cobalt are synthesized. Based on the analysis of X-ray diffraction profiles the conclusion is drawn about the formation of a hexagonal wurtzite type structure in the synthesized quantum dot (QD) solutions. The average crystallite sizes are 8 nm and 22 nm for the samples with manganese and cobalt respectively. Results of IR and optical spectroscopy are consistent with the powder X-ray diffraction and X-ray fluorescence data. The question about particle aggregation in isopropanol and DMF solutions is considered. The QD structures based on ZnS particles doped with Mn and Co transition metal atoms are modeled. The possibility to apply X-ray absorption near edge structure (XANES) spectroscopy to verify the atomic structure parameters around the positions of doping transition metal atoms in QDs of the ZnS family is shown. Partial densities of ZnS:Mn and ZnS:Co electronic states are calculated.