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1
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Homonuclear Separated Local-Field Spectroscopy by Magnetization-Exchange NMR

100%
Demco D. E., Filip X., Filip C., Chira D., Cozar O.
Acta Physica Polonica A
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1997
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vol. 92
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issue 6
1135-1149
EN
The possibility to perform homonuclear separated-local field NMR spectroscopy by magnetization-exchange is presented. Solid-state one-dimensional proton magnetization-exchange NMR is used to investigate intergroup residual dipolar couplings in cis-1,4-polybutadiene elastomer. A three-spin model is employed, in which the CH- and CH_{2}-protons are considered to be coupled by residual dipolar interactions. The magnetization-exchange process between the CH- and the CH_{2}-group in the regime of short mixing time provides valuable insight regarding molecular order. The spin-system response reflects well-localized dipolar interactions. The residual intergroup dipolar couplings are measured along the average polymer-chain direction for different temperatures. The dynamic order parameter along the chains is also evaluated.
2
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Single-Quantum NMR Spinning-Side-Band Patterns for Spin-3/2 System

100%
Lupulescu A., Fechete R., Demco D. E., Cozar O.
Acta Physica Polonica A
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1997
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vol. 92
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issue 6
1125-1134
EN
The NMR response of an isolated spin-3/2 system with an axially symmetric quadrupolar interaction under magic-angle sample spinning to an ideal radio-frequency pulse using irreducible tensor operators is evaluated analytically. The excited single-quantum spin coherences are modulated by the sample spinning. The effects of spinning frequency, quadrupole coupling constant and the orientation of quadrupolar interaction relative to rotor axis on the spinning-side-band patterns are simulated. High-resolution single-quantum spinning-side-band pattern detected for ^{23}Na (I=3/2) nuclei in sodium nitrate powder is compared with the simulation based on the theory and the quadrupole coupling is estimated.
3
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Ortho-Positronium Lifetime As a Detector of Spin-Crossover

80%
Bokor M., Marek T., Süvegh K., Böcskei Z., Buschmann J., Vértes A.
Acta Physica Polonica A
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1999
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vol. 95
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issue 4
469-473
EN
Positron lifetime parameters were measured for the spin-crossover complexes [Fe(R-1H-tetrazole)_{6}](BF_{4})_{2} (R = 1-ethyl, 1-n-propyl) and for the diamagnetic [Zn(1-n-propyl-1H-tetrazole)_{6}](BF_{4})_{2}. Positronium forms with significant intensity in the studied compounds. The ortho-para conversion of ortho-positronium was used to follow the spin-crossover. Changes of the dynamic structure were found in the propyltetrazole complex between 150 K and 90 K.
4
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Field Dependent Electron and Quadrupole Spin Relaxation: A Unified Treatment

70%
Kruk D.
Acta Physica Polonica A
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2007
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vol. 111
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issue 2
215-238
EN
This article reviews recent theoretical treatments of field dependent relaxation processes in complex systems containing mutually coupled dipolar, quadrupole, and electron spins. The presented approaches are based on an analogy between the Hamiltonian formalisms for quadrupole and zero field splitting interactions. Limitations of the presented treatments, resulting from the validity conditions of the second-order perturbation theory are discussed in detail.
5
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Theoretical Investigation of N-Methyl-N'-(4-nitrobenzylidene) pyrazine-2-carbohydrazide: Conformational Study, NBO Analysis, Molecular Structure and NMR Spectra

70%
Günay N., Tamer Ö., Kuzalic D., Avcı D., Atalay Y.
Acta Physica Polonica A
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2015
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vol. 127
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issue 3
701-710
EN
The crystal structure determination of the methylated pyrazine-2-carbohydrazide derivative, namely N-methyl-N'-(4-nitrobenzylidene)pyrazine-2-carbohydrazide were optimized to obtain its molecular geometric structure and electronic structures at the Hartree-Fock and density functional theory levels (B3LYP) with 6-311G(d,p) and 6-311++G(d,p) basis sets, using Gaussian 09W programme. The ^{1}H and ^{13}C nuclear magnetic resonance chemical shifts of the title molecule were calculated by using the gauge independent atomic orbital, continuous set of gauge transformations and individual gauges for atoms in molecules methods and were also compared with experimental values. The electronic properties high occupied and low unoccupied molecular orbitals energies were calculated and analyzed. Potential energy surface scan, natural population analysis and Mulliken atomic charges were investigated using theoretical calculations. A detailed molecular picture and intermolecular interactions arising from hyperconjugative interactions and charge delocalization of the molecule were analyzed using natural bond orbital analysis.
6
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Spectroscopic Studies of Poly(ε-Caprolactone)/Sodium Montmorillonite Nanocomposites

61%
Krzaczkowska J., Fojud Z., Kozak M., Jurga S.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
187-196
EN
Polymer-layered silicate nanocomposites belong to a new class of hybrid materials consisting of organic-synthetic polymer matrix and inorganic filler-layered structure clay minerals. The paper presents the results of FTIR, NMR, and SAXS studies of poly(ε-caprolactone)/sodium montmorillonite nanocomposites. We observed a correlation between the concentration of poly(ε-caprolactone) in nanocomposite samples and structural changes both of the clay mineral and the intercalated polymer. Stiffening of the clay structure appears as a result of poly(ε-caprolactone) intercalation into a clay structure. ^{27}Al NMR studies indicated in nanocomposites two non-equivalent sites of aluminium ions, i.e. in octahedral and tetrahedral coordination, whereas in the montmorillonite clay structure the aluminium ions are located in the interlayer space too. We found also that the temperatures of structural changes and softening process of poly(ε-caprolactone) chains in the nanocomposites depend on the concentration of poly(ε-caprolactone).
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