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1
Dougherty, Dennis A., S. Joshua Jacobs, Scott K. Silverman, Michael M. Murray, David A. Shultz, Anthony P. West und Jeffrey A. Clites. „New Organic Polymers And Molecules With Very High Spin States“. Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals 232, Nr. 1 (August 1993): 289–304. http://dx.doi.org/10.1080/10587259308035719.
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2
Estrada, Ernesto. „The electron density function of the Hückel (tight-binding) model“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, Nr. 2210 (Februar 2018): 20170721. http://dx.doi.org/10.1098/rspa.2017.0721.
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The Hückel (tight-binding) molecular orbital (HMO) method has found many applications in the chemistry of alternant conjugated molecules, such as polycyclic aromatic hydrocarbons (PAHs), fullerenes and graphene-like molecules, as well as in solid-state physics. In this paper, we found analytical expressions for the electron density matrix of the HMO method in terms of odd-powers of its Hamiltonian. We prove that the HMO density matrix induces an embedding of a molecule into a high-dimensional Euclidean space in which the separation between the atoms scales very well with the bond lengths of PAHs. We extend our approach to describe a quasi-correlated tight-binding model, which quantifies the number of unpaired electrons and the distribution of effectively unpaired electrons. In this case, we found that the corresponding density matrices induce embedding of the molecules into high-dimensional Euclidean spheres where the separation between the atoms contains information about the spin–spin repulsion between them. Using our approach, we found an analytic expression which explains the bond length alternation in polyenes inside the HMO framework. We also found that spin–spin interaction explains the alternation of distances between pairs of atoms separated by two bonds in conjugated molecules.
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Cui, Xing-Qian, Qian Liu, Zhi-Qiang Fan und Zhen-Hua Zhang. „Effects of oxygen adsorption on spin transport properties of single anthracene molecular devices“. Acta Physica Sinica 69, Nr. 24 (2020): 248501. http://dx.doi.org/10.7498/aps.69.20201028.
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With the miniaturization of molecular devices, high-performance nano devices can be fabricated by controlling the spin states of electrons. Because of their advantages such as low energy consumption, easy integration and long decoherence time, more and more attention has been paid to them. So far, the spin filtration efficiency of molecular device with graphene electrode is not very stable, which will decrease with the increase of voltage, and thus affecting its applications. Therefore, how to enhance the spin filtration efficiency of molecular device with graphene electrode becomes a scientific research problem. Using the first principle calculations based on density functional theory combined with non-equilibrium Green’s function, the physical mechanism of regulating the spin polarization transport properties of single anthracene molecule device with graphene nanoribon as electrode is investigated by molecular oxygen adsorption. In order to explore the effect of the change of the connection mode between single anthracene molecule and zigzag graphene nanoribbon electrode on the spin transport properties of the device, we establish two models. The first model is the model M1, which is the single anthracene molecule longitudinal connection, and the second model is the model M2, which is the single anthracene molecule lateral connection. The adsorption model of single oxygen molecule is denoted by M1O and M2O respectively. The results show that when none of oxygen molecules is adsorbed, the spin filtering effect of single anthracene molecule connecting graphene nanoribbons laterally (M2) is better than that of single anthracene molecule connecting graphene nanoribbons longitudinally (M1). After oxygen molecules are adsorbed on single anthracene molecule, the enhanced localized degree of transport eigenstate will make the spin current of the two kinds of devices decrease by nearly two orders of magnitude. However, molecular oxygen adsorption significantly improves the spin filtering efficiency of the device and enhances the application performance of the device. The maximal spin filtering efficiency of single anthracene molecule connecting graphene nanoribbons longitudinal (M1O) can be increased from 72% to 80%. More importantly, the device with single anthracene molecule connecting graphene nanoribbons laterally (M2) maintains nearly 100% spin filtering efficiency in a bias range from –0.5 V to +0.5 V. These results provide more theoretical guidance for practically fabricating spin molecular devices and regulating their spin transport properties.
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Jackowski, Karol, und Mateusz A. Słowiński. „Searching for the Best Values of NMR Shielding and Spin-Spin Coupling Parameters: CH4-nFn Series of Molecules as the Example“. Molecules 28, Nr. 3 (03.02.2023): 1499. http://dx.doi.org/10.3390/molecules28031499.
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Attempts at the theoretical interpretation of NMR spectra have a very long and fascinating history. Present quantum chemical calculations of shielding and indirect spin-spin couplings permit modeling NMR spectra when small, isolated molecules are studied. Similar data are also available from NMR experiments if investigations are performed in the gas phase. An interesting set of molecules is formed when a methane molecule is sequentially substituted by fluorine atoms—CH4-nFn, where n = 0, 1, 2, 3, or 4. The small molecules contain up to three magnetic nuclei, each with a one-half spin number. The spectral parameters of CH4-nFn can be easily observed in the gas phase and calculated with high accuracy using the most advanced ab initio methods of quantum chemistry. However, the presence of fluorine atoms makes the calculations of shielding and spin-spin coupling constants extremely demanding. Appropriate experimental 19F NMR parameters are good but also require some further improvements. Therefore, there is a real need for the comparison of existing NMR measurements with available state-of-the-art theoretical results for a better understanding of actual limits in the determination of the best shielding and spin-spin coupling values, and CH4-nFn molecules are used here as the exceptionally important case.
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Simpson, J. „Nuclear Shapes and Phases at Very High Spin“. Physica Scripta T23 (01.01.1988): 37–42. http://dx.doi.org/10.1088/0031-8949/1988/t23/005.
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Delgado, Teresa, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif und Céline Besnard. „Very Long-Lived Photogenerated High-Spin Phase of a Multistable Spin-Crossover Molecular Material“. Journal of the American Chemical Society 140, Nr. 40 (14.09.2018): 12870–76. http://dx.doi.org/10.1021/jacs.8b06042.
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Haeri, Blaffert, Schöffmann, Blech, Hartl, Garidel und Hinderberger. „Concentration Effects in the Interaction of Monoclonal Antibodies (mAbs) with their Immediate Environment Characterized by EPR Spectroscopy“. Molecules 24, Nr. 14 (10.07.2019): 2528. http://dx.doi.org/10.3390/molecules24142528.
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Monoclonal antibodies (mAbs) are often needed and applied in high concentration solutions, >100 mg/mL. Due to close intermolecular distances between mAbs at high concentrations (~10-20 nm at 200 mg/mL), intermolecular interactions between mAbs and mAbs and solvent/co-solute molecules become non-negligible. Here, EPR spectroscopy is used to study the high-concentration solutions of mAbs and their effect on co-solvated small molecules, using EPR “spin probing” assay in aqueous and buffered solutions. Such, information regarding the surrounding environments of mAbs at high concentrations were obtained and comparisons between EPR-obtained micro-viscosities (rotational correlation times) and macroscopic viscosities measured by rheology were possible. In comparison with highly viscous systems like glycerol-water mixtures, it was found that up to concentrations of 50 mg/mL, the mAb-spin probe systems have similar trends in their macro- (rheology) and micro-viscosities (EPR), whereas at very high concentrations they deviate strongly. The charged spin probes sense an almost unchanged aqueous solution even at very high concentrations, which in turn indicates the existence of large solvent regions that despite their proximity to large mAbs essentially offer pure water reservoirs for co-solvated charged molecules. In contrast, in buffered solutions, amphiphilic spin probes like TEMPO interact with the mAb network, due to slight charge screening. The application of EPR spectroscopy in the present work has enabled us to observe and discriminate between electrostatic and hydrophobic kinds of interactions and depict the potential underlying mechanisms of network formation at high concentrations of mAbs. These findings could be of importance as well for the development of liquid-liquid phase separations often observed in highly concentrated protein solutions.
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Furman, Gregory, und Shaul Goren. „Spin-Lattice Relaxation of Dipolar Energy in Fluid Confined to Nanosize Cavities“. Materials Science Forum 721 (Juni 2012): 47–52. http://dx.doi.org/10.4028/www.scientific.net/msf.721.47.
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We shown that by means of the two pulse sequence, the spin system of a liquid entrapped into nanosize cavities can be prepared in quasi-equilibrium states of high dipolar order. Then the dipolar order relaxes to thermal equilibrium with the lattice with a relaxation time T1d. It was shown that large number of spins T1d increases as the square to the concentration of the molecules C and decreases as inverse of the number of spins, T1d - C²/N. Study of spin lattice relaxation of dipolar energy in a spin system under the bounded region is important for extracting very useful parameter characterized nanomaterials from NMR experimental data.
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Ghosh, Pratyush, Antonios M. Alvertis, Rituparno Chowdhury, Petri Murto, Alexander J. Gillett, Shengzhi Dong, Alexander J. Sneyd et al. „Decoupling excitons from high-frequency vibrations in organic molecules“. Nature 629, Nr. 8011 (08.05.2024): 355–62. http://dx.doi.org/10.1038/s41586-024-07246-x.
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AbstractThe coupling of excitons in π-conjugated molecules to high-frequency vibrational modes, particularly carbon–carbon stretch modes (1,000–1,600 cm−1) has been thought to be unavoidable1,2. These high-frequency modes accelerate non-radiative losses and limit the performance of light-emitting diodes, fluorescent biomarkers and photovoltaic devices. Here, by combining broadband impulsive vibrational spectroscopy, first-principles modelling and synthetic chemistry, we explore exciton–vibration coupling in a range of π-conjugated molecules. We uncover two design rules that decouple excitons from high-frequency vibrations. First, when the exciton wavefunction has a substantial charge-transfer character with spatially disjoint electron and hole densities, we find that high-frequency modes can be localized to either the donor or acceptor moiety, so that they do not significantly perturb the exciton energy or its spatial distribution. Second, it is possible to select materials such that the participating molecular orbitals have a symmetry-imposed non-bonding character and are, thus, decoupled from the high-frequency vibrational modes that modulate the π-bond order. We exemplify both these design rules by creating a series of spin radical systems that have very efficient near-infrared emission (680–800 nm) from charge-transfer excitons. We show that these systems have substantial coupling to vibrational modes only below 250 cm−1, frequencies that are too low to allow fast non-radiative decay. This enables non-radiative decay rates to be suppressed by nearly two orders of magnitude in comparison to π-conjugated molecules with similar bandgaps. Our results show that losses due to coupling to high-frequency modes need not be a fundamental property of these systems.
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Caselli, P., O. Sipilä und J. Harju. „Deuterated forms of H 3 + and their importance in astrochemistry“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, Nr. 2154 (05.08.2019): 20180401. http://dx.doi.org/10.1098/rsta.2018.0401.
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At the low temperatures (approx. 10 K) and high densities (approx. 100 000 H 2 molecules per cm −3 ) of molecular cloud cores and protostellar envelopes, a large amount of molecular species (in particular those containing C and O) freeze-out onto dust grain surfaces. It is in these regions that the deuteration of H 3 + becomes very efficient, with a sharp abundance increase of H 2 D + and D 2 H + . The multi-deuterated forms of H 3 + participate in an active chemistry: (i) their collision with neutral species produces deuterated molecules such as the commonly observed N 2 D + , DCO + and multi-deuterated NH 3 ; (ii) their dissociative electronic recombination increases the D/H atomic ratio by several orders of magnitude above the D cosmic abundance, thus allowing deuteration of molecules (e.g. CH 3 OH and H 2 O) on the surface of dust grains. Deuterated molecules are the main diagnostic tools of dense and cold interstellar clouds, where the first steps toward star and protoplanetary disc formation take place. Recent observations of deuterated molecules are reviewed and discussed in view of astrochemical models inclusive of spin-state chemistry. We present a new comparison between models based on complete scrambling (to calculate branching ratio tables for reactions between chemical species that include protons and/or deuterons) and models based on non-scrambling (proton hop) methods, showing that the latter best agree with observations of NH 3 deuterated isotopologues and their different nuclear spin symmetry states. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.
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Möbius, Klaus, Wolfgang Lubitz, Nicholas Cox und Anton Savitsky. „Biomolecular EPR Meets NMR at High Magnetic Fields“. Magnetochemistry 4, Nr. 4 (06.11.2018): 50. http://dx.doi.org/10.3390/magnetochemistry4040050.
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In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.
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FERNANDEZ, JOSÉ M., SETH LLOYD, TAL MOR und VWANI ROYCHOWDHURY. „ALGORITHMIC COOLING OF SPINS: A PRACTICABLE METHOD FOR INCREASING POLARIZATION“. International Journal of Quantum Information 02, Nr. 04 (Dezember 2004): 461–77. http://dx.doi.org/10.1142/s0219749904000419.
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An efficient technique to generate ensembles of spins that are highly polarized by external magnetic fields is the Holy Grail in Nuclear Magnetic Resonance (NMR) spectroscopy. Since spin-half nuclei have steady-state polarization biases that increase inversely with temperature, spins exhibiting high polarization biases are considered cool, even when their environment is warm. Existing spin-cooling techniques are highly limited in their efficiency and usefulness. Algorithmic cooling is a promising new spin-cooling approach that employs data compression methods in open systems. It reduces the entropy of spins on long molecules to a point far beyond Shannon's bound on reversible entropy manipulations, thus increasing their polarization. Here we present an efficient and experimentally feasible algorithmic cooling technique that cools spins to very low temperatures even on short molecules. This practicable algorithmic cooling could lead to breakthroughs in high-sensitivity NMR spectroscopy in the near future, and to the development of scalable NMR quantum computers in the far future. Moreover, while the cooling algorithm itself is classical, it uses quantum gates in its implementation, thus representing the first short-term application of quantum computing devices.
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Matsui, Hiroshi, Yi-Fei Zhu und Edward R. Grant. „High-Resolution Non-Resonant Two-Photon Threshold Photoionization of Propyne“. Laser Chemistry 16, Nr. 3 (01.01.1996): 151–56. http://dx.doi.org/10.1155/1996/13869.
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Using techniques of delayed pulsed-field ionization zero-kinetic-energy (ZEKE) photoelectron spectroscopy, we have resolved spin-orbit structure in the rotational profile of the origin band in the non-resonant two-photon threshold photoionization of propyne. Both the rotational and spin-orbit characteristics of this band are well-simulated by a simple model that assumes the spin-orbit splitting of acetylene cation in combination with the rotational constants of the neutral propyne ground state. This result, combined with very little evidence for photoionizing transitions terminating on vibronically excited states, suggests that the structure of the propyne cation structure is very close to that of the neutral ground state and very little altered by Jahn-Teller distortion.
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Rat, Sylvain, José Sánchez Costa, Salma Bedoui, William Nicolazzi, Gábor Molnár, Lionel Salmon und Azzedine Bousseksou. „Investigation of nucleation and growth phenomena during the thermal and light induced spin transition in the [Fe(1-bpp)2][BF4]2 complex“. Pure and Applied Chemistry 87, Nr. 3 (01.03.2015): 261–70. http://dx.doi.org/10.1515/pac-2014-1002.
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AbstractOptical microscopy measurements have been realized on single crystals of the [Fe(1-bpp)2][BF4]2 complex (1-bpp=2,6-di(pyrazol-1-yl)pyridine). The thermal spin transition around 253 K occurs by a heterogeneous nucleation and growth mechanism and involves a clear phase separation and a small hysteresis. This very abrupt and complete thermal transition is preceded by a premonitory spin conversion, which implies only a small fraction (ca. 2–3 %) of the molecules. This peculiar behavior may be the sign of heterophase fluctuations. The light-induced spin transition from the stable low spin (LS) to the metastable high spin (HS) phase was achieved at 80 K by focusing laser light into a small volume fraction of the crystal. Under continuous irradiation this photo-converted HS “nucleus” then grows and the whole crystal converts to the HS phase providing evidence for a light-induced instability in the system due to long-range elastic interactions. The relaxation of the light-induced metastable HS phase at 83 K follows a sigmoidal decay – typical of cooperative spin crossover systems. Nevertheless the spatial development of this relaxation process appears very homogeneous and no phase separation could be detected within the resolution of the optical microscope.
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Nurushev, S. B. „Summary of Experimental Data on High Energy Spin Physics“. International Journal of Modern Physics A 12, Nr. 20 (10.08.1997): 3433–76. http://dx.doi.org/10.1142/s0217751x97001808.
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High Energy Spin Physics has made significant progress. During a very short period a set of new phenomena have been established — relevant to the spin structure of the nucleons, hyperon polarization, the single- and double-spin asymmetries. The recent advent of the polarized proton and antiproton beams, and unpolarized Σ - beam opened a new avenue for study of spin physics at high energy, like the flavor dependence of the spin effect, the spin transfer mechanism, the comparative study of the hyperon polarization and analyzing power, etc. These and other news in High Energy Spin Physics are discussed in this review.
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Fürmeyer, Fabian, Luca M. Carrella und Eva Rentschler. „2D Layer Arrangement of Solely [HS-HS] or [LS-LS] Molecules in the [HS-LS] State of a Dinuclear Fe(II) Spin Crossover Complex“. Crystals 10, Nr. 6 (31.05.2020): 448. http://dx.doi.org/10.3390/cryst10060448.
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Herein we report the synthesis and characterization of three new dinuclear iron(II) complexes [FeII2(I4MTD)2](F3CSO3)4 (C1), [FeII2(I4MTD)2](ClO4)4 (C2) and [FeII2(I4MTD)2](BF4)4 (C3) based on the novel ligand (I4MTD = 2,5-bis{[(1H-imidazol-4-ylmethyl)amino]methyl}-1,3,4-thiadiazole). Magnetic susceptibility measurements and single-crystal structure analysis show that the iron(II) spin centers for all complexes are in the high spin state at high temperatures. While the magnetic data of air-dried samples confirm the [HS-HS] state for C1 and C2 down to very low temperature, for C3, a gradual spin crossover is observed below 150 K. The crystal structure of C3·THF at 100 K shows that a spin transition from [HS-HS] to an intermediate state takes place, which is a 1:1 mixture of discrete [HS-HS] and [LS-LS] molecules, as identified unambiguously by crystallography. The different SCO properties of C1–C3 can be attributed to crystal packing effects in the solid state.
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Ossinger, Sascha, Christian Näther und Felix Tuczek. „Crystal structure of bis{(3,5-dimethylpyrazol-1-yl)dihydro[3-(pyridin-2-yl)pyrazol-1-yl]borato}iron(II)“. Acta Crystallographica Section E Crystallographic Communications 76, Nr. 8 (10.07.2020): 1266–70. http://dx.doi.org/10.1107/s2056989020009214.
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The structure determination of [Fe(C13H15BN5)2] was undertaken as part of a project on the modification of the recently published spin-crossover (SCO) complex [Fe{H2B(pz)(pypz)}2] (pz = pyrazole, pypz = pyridylpyrazole). To this end, a new ligand was synthesized in which two additional methyl groups are present. Its reaction with iron trifluoromethanesulfonate led to a pure sample of the title compound, as proven by X-ray powder diffraction. The asymmetric unit consists of one complex molecule in a general position. The FeII atom is coordinated by two tridentate N-binding {H2B(3,5-(CH3)2-pz)(pypz)}− ligands. The Fe—N bond lengths range between 2.1222 (13) and 2.3255 (15) Å, compatible with FeII in the high-spin state, which was also confirmed by magnetic measurements. Other than a very weak C—H...N non-classical hydrogen bond linking individual molecules into rows extending parallel to [010], there are no remarkable intermolecular interactions.
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HARTMANN-BOUTRON, FRANÇOISE, PAOLO POLITI und JACQUES VILLAIN. „TUNNELING AND MAGNETIC RELAXATION IN MESOSCOPIC MOLECULES“. International Journal of Modern Physics B 10, Nr. 21 (30.09.1996): 2577–637. http://dx.doi.org/10.1142/s0217979296001148.
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The relaxation of the magnetization in big molecular groups embedded in crystals is studied and compared with experimental data on Mn 12 O 12. At sufficiently high temperatures (T > 2 K in Mn 12 O 12) the relaxation is thermally activated, and the exchange of energy with phonons produces relaxation through a cascade of elementary transitions where the component Sz of the spin along the tetragonal axis changes by δm = ±1 or ±2. At lower temperatures, tunneling occurs, but energy conservation requires exchange of energy with nuclear spins in very low magnetic fields (smaller than the hyperfine field), or with phonons in higher field. The phonon assisted tunneling rate 1/τ is proportional to H 3 for weak fields H(H < 2 Tesla ). A minimum of τ is expected when the field is of the order of magnitude of the maximum hyperfine field. The theoretically predicted minimum is sharper and should occur at a field value four times as small than experimentally observed.
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Fu, Zhendong, Zhong-Wen Ouyang, Qian-Cheng Luo, Yan-Zhen Zheng, Wei Tong, Huanpeng Bu, Hanjie Guo und Jin-Kui Zhao. „Zero-Field Splitting in Cyclic Molecular Magnet {Cr8Y8}: A High-Frequency ESR Study“. Magnetochemistry 9, Nr. 2 (03.02.2023): 49. http://dx.doi.org/10.3390/magnetochemistry9020049.
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Cyclic 3d-4f molecular magnets have received considerable attention owing to their potential applications in high-density data storage and quantum information processing. As a rare example of ferromagnetic polynuclear Cr rings, {Cr8Y8} represents a valuable test bed to directly study the magnetic interaction between Cr3+ ions in large hexadecametallic {Cr8Ln8} (Ln = 4f metal) molecules. We have proposed a “single-J” model to approximate the low-temperature spin dynamics of {Cr8Y8} in our earlier study, while a zero-field splitting (ZFS) of the quantum levels was also suggested by the heat capacity data. In order to have a deeper understanding of the magnetism of {Cr8Y8}, it is necessary to verify the ZFS by means of high-resolution spectral methods and identify its origin. In this work, we present a high-frequency electron spin resonance (HF-ESR) study on the ZFS of {Cr8Y8}. The X-band ESR spectra consists of multi-peak structure, indicative of magnetic anisotropy that breaks the degeneracy between spin states in the absence of a magnetic field. HF-ESR spectra are collected to extract the ZFS parameters. We observed a sharp resonance peak due to the transitions between the S = 11 quantum levels and a broadband corresponding to a distribution of resonance peaks due to the ZFS of the S = 12 quantum levels. By analyzing HF-ESR spectra, we confirm the expected S = 12 ground state and determine its ZFS parameter D as −0.069 K, and, furthermore, we reproduce the spectra recorded at 154 GHz. The macrospin model proves to still be valid. The ZFS is attributed to the axial magnetic anisotropy, as found in some other Cr-based molecular wheels. The detailed HF-ESR investigation presented in this paper will benefit the studies on other {Cr8Ln8} wheels with magnetic Ln3+ ions and highlights the importance of the HF-ESR method as a high-resolution probe in determining the ZFS parameters with very small magnitude.
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Smith, J. A. S. „Nuclear Quadrupole Resonance: The Present State and Further Development“. Zeitschrift für Naturforschung A 41, Nr. 1-2 (01.02.1986): 453–62. http://dx.doi.org/10.1515/zna-1986-1-289.
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The importance of nuclear electric quadrupole interactions in chemistry, both present and future, depends very much on their power to resolve problems in electronic structure and molecular dynamics. Fortunately, the subject, by its very nature, is “multinuclear”; even if the ground state of a given nucleus is non-quadrupolar, there often exist excited nuclear states which are, an example being 19F, for which quadrupole coupling constants are now being published from angular correlation measurements. Other new techniques are constantly extending the range of the experiments, recent examples being the use of SQUID magnetometers to detect acoustic 121Sb and 123Sb quadrupole resonance in antimony metal and Fourier transform quadrupole resonance spectroscopy based on fast field cycling to measure 2H quadrupole interactions in powders. Recently, much work on quadrupole interactions in solids of half-integral spin nuclei such as 17O or 27Al has been pursued in two different ways; by quadrupole double resonance in natural abundance, and nuclear magnetic resonance in very high magnetic fields, for which enrichment of low-abundance nuclei such as 170 is often required. In the liquid phase, measurements are now sufficiently reliable for comparisons of changes in the nuclear electric quadrupole tensor from gas to liquid and solid phases to be made. The new methods of partial alignment of polar molecules in the liquid phase in strong electric fields, or magnetically anisotropic molecules in high magnetic fields, seem certain to contribute to these developments.
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Cruz, C., P. J. Sebastião, J. Figueirinhas, A. C. Ribeiro, H. T. Nguyen, C. Destrade und F. Noack. „NMR Study of Molecular Dynamics in a D ho Columnar Mesophase“. Zeitschrift für Naturforschung A 53, Nr. 10-11 (01.11.1998): 823–27. http://dx.doi.org/10.1515/zna-1998-10-1104.
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Abstract In this paper we report the first molecular dynamics study combining fast field-cycling and conven-tional NMR techniques in a thermotropic liquid crystal of discotic molecules exhibiting an ordered columnar hexagonal mesophase. Using the association of these techniques we obtained proton T1 data over a very large domain of Larmor frequencies (ω/2π from 500 Hz to 85 MHz). The proton spin-lattice relaxation results were analysed considering the structure of the mesophase and the types of movements which are expected to influence significantly the relaxation rate, namely local molecu-lar rotational reorientations, inter-columnar self-diffusion and collective movements corresponding to bending and compression of the columns. We verified that these mechanisms dominate the relaxation respectively for high, medium and low Larmor frequencies.
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Helliwell, John. „Synchrotron radiation macromolecular crystallography: our science and spin offs“. Acta Crystallographica Section A Foundations and Advances 70, a1 (05.08.2014): C10. http://dx.doi.org/10.1107/s2053273314099896.
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I will give an overview of synchrotron radiation (SR) in macromolecular crystallography (MX) instrumentation, methods and applications from the early days to the present, including the evolution of SR sources and on to the `ultimate storage ring'. The build of dedicated beamlines for resonant anomalous scattering, large unit cells, ever smaller crystals and studies up to ultra-high resolution are core benefits. Results include a high output of PDB depositions, the successful use of microcrystals, pushing the frontiers of using high and low photon energies and time-resolved structural studies at even sub-nanosecond resolutions. These intensively physics based developments will be complemented by biological and chemical crystallography research results, encompassing catalysis and marine coloration, as well as the public understanding of our science and its impacts. Spin off benefits include services to the pharmaceutical industry and helping develop chemical crystallography uses of SR. The development of the Laue method with SR has led to pioneering spin off developments in neutron MX, including transfer of the well validated Daresbury Laue software to various neutron facilities worldwide. Neutron MX is gathering pace as new instrumentation and dedicated sample preparation facilities are in place at reactor and spallation neutron sources; smaller samples and much larger molecular weight protein complexes are now feasible for investigation so as to establish their protonation states and bound water structure. With the X-ray lasers, closely linked to the SR developments, we anticipate the use of ever smaller samples such as nanocrystals, nanoclusters and single molecules, as well as opening up femtosecond time-resolved diffraction structural studies. At the SR sources, a very high throughput assessment for the best crystal samples and tackling sub-micron crystals will become widespread.
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BARGER, V., J. OHNEMUS und R. J. N. PHILLIPS. „SPIN CORRELATION EFFECTS IN THE HADROPRODUCTION AND DECAY OF VERY HEAVY TOP QUARK PAIRS“. International Journal of Modern Physics A 04, Nr. 03 (Februar 1989): 617–25. http://dx.doi.org/10.1142/s0217751x89000297.
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Density matrix techniques in the helicity basis allow us to write down explicitly the squared matrix elements for tree-level hadroproduction and weak decay of very heavy top quark pairs, that decay before hadronization. This treatment includes the full effects of quark spin correlation. We illustrate the effects of spin correlation on physical distributions in [Formula: see text] dilepton events, [Formula: see text], [Formula: see text], [Formula: see text], for the case mt =120 GeV at [Formula: see text], the energy of the Tevatron collider. The effects of spin correlation are quantitatively small compared to calculations that ignore them, giving corrections of order 10% or less in the physical distributions studied.
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Ulman, Kanchan, Mighfar Imam, Shobhana Narasimhan, Anders Odell und Anna Delin. „Theoretical Study of Spin Conduction in the Ni/DTE/Ni Nanohybrid“. Nano Hybrids 4 (Mai 2013): 1–20. http://dx.doi.org/10.4028/www.scientific.net/nh.4.1.
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The photoswitching molecule dithienylethene (DTE) is an interesting candidate for constructing optoelectronic molecular devices since it can be made to switch between a closed and an open conformation using light. We here report computations, based on density functional theory (DFT) and the non-equilibrium Green function (NEGF) method, of the spin-resolved conductance of the two DTE isomers attached to spin-polarized nickel leads. Results are compared and contrasted to those of other contact materials (nonmagnetic Ni, Ag, and Au), analyzing the physical origins of the various features in the transmission function. It was found rather surprisingly, that the two spin channels in the Ni/DTE/Ni device have almost identical I-V characteristics, despite one channel being d-dominated and the other one s-dominated. It was also observed that the Ni-based device exhibits a sustained high conductance ratio also for high bias - a property that may be of relevance in future device design. Furthermore, two computational schemes for calculating the conductance were compared and analyzed. It was found that even for very small bias the molecular orbital polarization was decisive for spin-related properties such as the spin current ratio and magneto-resistance in the Ni/DTE/Ni device.
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Kajiwara, Takashi, Hiroki Tanaka und Masahiro Yamashita. „Single-chain magnets constructed with a twisting arrangement of the easy-plane of iron(II) ions“. Pure and Applied Chemistry 80, Nr. 11 (01.01.2008): 2297–308. http://dx.doi.org/10.1351/pac200880112297.
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A novel class of single-chain magnets (SCMs), catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 and its derivative, were synthesized using the spin-carrier components possessing hard-axis anisotropy (or easy-plane anisotropy, D > 0). The easy-axis-type anisotropy of whole molecules of these compounds, which is essential for the formation of SCMs, arises from the twisted arrangement of easy-planes of Fe(II) along the chain axis. Alternating high-spin Fe(II) and low-spin Fe(III) chain complexes behave as an SCM with a typical frequency-dependent ac susceptibility which obeys Arrhenius law. Below 7 K, catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 showed a short-range spin-ordering even in zero external field in a time range of Mössbauer spectroscopy as well as the muon-spin-relaxation (μSR) spectroscopy. Since the easy-axis-type magnetic anisotropy originated from the structural motif of the twisting arrangement of Fe(II) ions, the overall magnetic property was very sensitive to the small structural changes arising from adsorption/desorption of the crystal solvents, and catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 showed a reversible change in magnetism that has been referred to as "a magnetic sponge". In its derivative, controls of the molecular structure, the arrangement of chains in the crystal, and magnetic properties both in dc and ac susceptibility have been achieved by the introduction of methyl group on a bpca- ligand, which bridges and mediates the magnetic interaction of the adjoining Fe(II)/Fe(III) ions.
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Helliwell, John R., und Edward P. Mitchell. „Synchrotron radiation macromolecular crystallography: science and spin-offs“. IUCrJ 2, Nr. 2 (03.02.2015): 283–91. http://dx.doi.org/10.1107/s205225251402795x.
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A current overview of synchrotron radiation (SR) in macromolecular crystallography (MX) instrumentation, methods and applications is presented. Automation has been and remains a central development in the last decade, as have the rise of remote access and of industrial service provision. Results include a high number of Protein Data Bank depositions, with an increasing emphasis on the successful use of microcrystals. One future emphasis involves pushing the frontiers of using higher and lower photon energies. With the advent of X-ray free-electron lasers, closely linked to SR developments, the use of ever smaller samples such as nanocrystals, nanoclusters and single molecules is anticipated, as well as the opening up of femtosecond time-resolved diffraction structural studies. At SR sources, a very high-throughput assessment for the best crystal samples and the ability to tackle just a few micron and sub-micron crystals will become widespread. With higher speeds and larger detectors, diffraction data volumes are becoming long-term storage and archiving issues; the implications for today and the future are discussed. Together with the rise of the storage ring to its current pre-eminence in MX data provision, the growing tendency of central facility sites to offer other centralized facilities complementary to crystallography, such as cryo-electron microscopy and NMR, is a welcome development.
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Marques, Rafaela T., Frederico F. Martins, Deniz F. Bekiş, Ana I. Vicente, Liliana P. Ferreira, Clara S. B. Gomes, Sónia Barroso et al. „The Halogen Effect on the Magnetic Behaviour of Dimethylformamide Solvates in [Fe(halide-salEen)2]BPh4“. Magnetochemistry 8, Nr. 12 (22.11.2022): 162. http://dx.doi.org/10.3390/magnetochemistry8120162.
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Complexes [Fe(X-salEen)2]BPh4·DMF, with X = Br (1), Cl (2), and F (3), were crystallised from N-ethylethylenediamine with the aim of understanding the role of a high boiling point N,N′-dimethylformamide solvate in the spin crossover phenomenon. The counter ion was chosen for only being able to participate in weak intermolecular interactions. The compounds were structurally characterised by single crystal X-ray diffraction. Complex 1 crystallised in the orthorhombic space group P212121, and complexes 2 and 3 in the monoclinic space group P21/n. Even at room temperature, low spin was the predominant form, although complex 2 exhibited the largest proportion of the high-spin species according to both the magnetisation measurements and the Mössbauer spectra. Density Functional Theory calculations were performed both on the periodic solids and on molecular models for complexes 1–3 and the iodide analogue 4. While all approaches reproduced the experimental structures very well, the energy balance between the high-spin and low-spin forms was harder to reproduce, though some calculations pointed to the easier spin crossover of complex 2, as observed. Periodic calculations with the functional PBE led to very similar ΔEHS-LS values for all complexes but showed a preference for the low-spin form. However, the single-point calculations with B3LYP* showed, for the model without solvate, that the Cl complex should undergo spin crossover more easily. The molecular calculations also reflected this fact, which was more clearly defined when the cation–anion–solvate model was used. In the other models there was not much difference between the Cl, Br, and I complexes.
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Benakli, Karim. „High frequency gravitational waves from spin-3/2 fields“. International Journal of Modern Physics A 35, Nr. 36 (30.12.2020): 2044029. http://dx.doi.org/10.1142/s0217751x20440297.
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We point out the peculiar form of the gravitational wave signal expected from a gas of particles carry spin-3/2 produced during preheating. Given the very few ways that gravitinos can manifest themselves in an experimentally observable way, we stress the importance of improving the sensitivity of ultrahigh frequency detectors in the future. This review is based on work that appeared in Ref. 1.
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Durán Caballero, Laura, Christoph Schran, Fabien Brieuc und Dominik Marx. „Neural network interaction potentials for para-hydrogen with flexible molecules“. Journal of Chemical Physics 157, Nr. 7 (21.08.2022): 074302. http://dx.doi.org/10.1063/5.0100953.
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The study of molecular impurities in para-hydrogen ( pH2) clusters is key to push forward our understanding of intra- and intermolecular interactions, including their impact on the superfluid response of this bosonic quantum solvent. This includes tagging with only one or very few pH2, the microsolvation regime for intermediate particle numbers, and matrix isolation with many solvent molecules. However, the fundamental coupling between the bosonic pH2 environment and the (ro-)vibrational motion of molecular impurities remains poorly understood. Quantum simulations can, in principle, provide the necessary atomistic insight, but they require very accurate descriptions of the involved interactions. Here, we present a data-driven approach for the generation of impurity⋯ pH2 interaction potentials based on machine learning techniques, which retain the full flexibility of the dopant species. We employ the well-established adiabatic hindered rotor (AHR) averaging technique to include the impact of the nuclear spin statistics on the symmetry-allowed rotational quantum numbers of pH2. Embedding this averaging procedure within the high-dimensional neural network potential (NNP) framework enables the generation of highly accurate AHR-averaged NNPs at coupled cluster accuracy, namely, explicitly correlated coupled cluster single, double, and scaled perturbative triples, CCSD(T*)-F12a/aVTZcp, in an automated manner. We apply this methodology to the water and protonated water molecules as representative cases for quasi-rigid and highly flexible molecules, respectively, and obtain AHR-averaged NNPs that reliably describe the corresponding H2O⋯ pH2 and H3O+⋯ pH2 interactions. Using path integral simulations, we show for the hydronium cation, H3O+, that umbrella-like tunneling inversion has a strong impact on the first and second pH2 microsolvation shells. The automated and data-driven nature of our protocol opens the door to the study of bosonic pH2 quantum solvation for a wide range of embedded impurities.
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Chiesa, A., P. Santini, E. Garlatti, F. Luis und S. Carretta. „Molecular nanomagnets: a viable path toward quantum information processing?“ Reports on Progress in Physics 87, Nr. 3 (05.02.2024): 034501. http://dx.doi.org/10.1088/1361-6633/ad1f81.
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Abstract Molecular nanomagnets (MNMs), molecules containing interacting spins, have been a playground for quantum mechanics. They are characterized by many accessible low-energy levels that can be exploited to store and process quantum information. This naturally opens the possibility of using them as qudits, thus enlarging the tools of quantum logic with respect to qubit-based architectures. These additional degrees of freedom recently prompted the proposal for encoding qubits with embedded quantum error correction (QEC) in single molecules. QEC is the holy grail of quantum computing and this qudit approach could circumvent the large overhead of physical qubits typical of standard multi-qubit codes. Another important strength of the molecular approach is the extremely high degree of control achieved in preparing complex supramolecular structures where individual qudits are linked preserving their individual properties and coherence. This is particularly relevant for building quantum simulators, controllable systems able to mimic the dynamics of other quantum objects. The use of MNMs for quantum information processing is a rapidly evolving field which still requires to be fully experimentally explored. The key issues to be settled are related to scaling up the number of qudits/qubits and their individual addressing. Several promising possibilities are being intensively explored, ranging from the use of single-molecule transistors or superconducting devices to optical readout techniques. Moreover, new tools from chemistry could be also at hand, like the chiral-induced spin selectivity. In this paper, we will review the present status of this interdisciplinary research field, discuss the open challenges and envisioned solution paths which could finally unleash the very large potential of molecular spins for quantum technologies.
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Haines, Julian, und D. F. R. Gilson. „Phase transitions in solid cycloheptene“. Canadian Journal of Chemistry 68, Nr. 4 (01.04.1990): 604–11. http://dx.doi.org/10.1139/v90-093.
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The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.
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Kusz, Joachim, Dieter Schollmeyer, Hartmut Spiering und Philipp Gütlich. „The LIESST state of [Fe(pic)3]Cl2.EtOH – the superstructure under continuous irradiation“. Journal of Applied Crystallography 38, Nr. 3 (13.05.2005): 528–36. http://dx.doi.org/10.1107/s0021889805009891.
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The superstructure recently discovered in [Fe(pic)3]Cl2.EtOH at temperatures inside the step region of the high-spin–low-spin transition curve sheds new light on the anomalous transition behaviour in spin crossover compounds. The structure of the metastable LIESST state of [Fe(pic)3]Cl2.EtOH at 10 K has been measured. The decay has been followed by X-ray diffraction using a CCD camera in order to detect reflections of the superstructure building up during the decay. No signal above the noise of the CCD camera was observed, so that even diffuse scattering could not be detected. This finding is in agreement with correlation lengths of pair correlations of molecules in the HS and LS states being very short, as was concluded earlier from the shape of the decay curves of the HS fraction by theoretical considerations [Romstedt et al. (1998). J. Phys. Chem. Solids, 59, 265–275]. The crystal structure inside the step at 118 K has also been studied under continuous irradiation. The temperature range of the superstructure and the degree of order could be changed by continuous irradiation with green laser light, indicating an increase of the lifetime of the HS excited state by several orders of magnitude compared with the temperature regions outside.
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Sil, Debangsu, Sayantani Banerjee, Sudip Kumar Ghosh und Sankar Prasad Rath. „Fluoro-bridged dimanganese(III) porphyrin dimer: Effect of intermacrocyclic interactions in modulating metal spin state“. Journal of Porphyrins and Phthalocyanines 25, Nr. 05n06 (31.03.2021): 522–32. http://dx.doi.org/10.1142/s1088424621500401.
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The synthesis, structure, and spectroscopic properties of a remarkably deformed dimanganese(III)-[Formula: see text]-fluoro porphyrin dimer in connection to its diiron(III) [Formula: see text]-fluoro and [Formula: see text]-hydroxo counterparts is reported. It is the most recent addition to the continued effort in understanding the effect of intermacrocyclic interaction on the molecular structure and properties of di-heme proteins. The dimanganese(III)-[Formula: see text]-fluoro porphyrin dimer, similar to its [Formula: see text]-hydroxo analogs, stabilizes two equivalent high-spin ([Formula: see text]= 2) manganese(III) centers. This is in contrast to the diiron(III) analogs where the [Formula: see text]-hydroxo complex stabilizes two inequivalent iron(III) centers with two different spin states of iron in the same molecule while the [Formula: see text]-fluoro complex stabilizes two equivalent metal centers with intermediate spin ([Formula: see text]= 3/2) state. The present results further establish the extreme interdependence of the energetically accessible spin states of the metal and the extent of porphyrin core deformation. It is very likely that nature utilizes the same powerful tool to modulate large change in the electronic structure and properties of the heme center needed for its function.
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Gong, Haoyu, Jinyi Lin und Huibin Sun. „Nanocrystal Array Engineering and Optoelectronic Applications of Organic Small-Molecule Semiconductors“. Nanomaterials 13, Nr. 14 (17.07.2023): 2087. http://dx.doi.org/10.3390/nano13142087.
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Organic small-molecule semiconductor materials have attracted extensive attention because of their excellent properties. Due to the randomness of crystal orientation and growth location, however, the preparation of continuous and highly ordered organic small-molecule semiconductor nanocrystal arrays still face more challenges. Compared to organic macromolecules, organic small molecules exhibit better crystallinity, and therefore, they exhibit better semiconductor performance. The formation of organic small-molecule crystals relies heavily on weak interactions such as hydrogen bonds, van der Waals forces, and π–π interactions, which are very sensitive to external stimuli such as mechanical forces, high temperatures, and organic solvents. Therefore, nanocrystal array engineering is more flexible than that of the inorganic materials. In addition, nanocrystal array engineering is a key step towards practical application. To resolve this problem, many conventional nanocrystal array preparation methods have been developed, such as spin coating, etc. In this review, the typical and recent progress of nanocrystal array engineering are summarized. It is the typical and recent innovations that the array of nanocrystal array engineering can be patterned on the substrate through top-down, bottom-up, self-assembly, and crystallization methods, and it can also be patterned by constructing a series of microscopic structures. Finally, various multifunctional and emerging applications based on organic small-molecule semiconductor nanocrystal arrays are introduced.
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Gupta, V., R. Huerta und G. Sánchez-Colón. „Sea Contributions to Spin 1/2 Baryon Structure, Magnetic Moments, and Spin Distribution“. International Journal of Modern Physics A 12, Nr. 10 (20.04.1997): 1861–74. http://dx.doi.org/10.1142/s0217751x97001171.
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We treat the baryon as a composite system made out of a "core" of three quarks (as in the standard quark model) surrounded by a "sea" (of gluons and [Formula: see text]-pairs) which is specified by its total quantum numbers like flavor, spin and color. Specifically, we assume the sea to be a flavor octet with spin 0 or 1 but no color. The general wave function for spin 1/2 baryons with such a sea component is given. Application to the magnetic moments is considered. Numerical analysis shows that a scalar (spin 0) sea with an admixture of a vector (spin 1) sea can provide very good fits to the magnetic moment data using experimental errors. These fit also give reasonable values for the spin distributions of the proton and neutron.
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Summa, Francesco Ferdinando, und Roberta Citro. „Many Body Current Density from Foldy–Wouthuysen Transformation of the Dirac–Coulomb Hamiltonian“. Physchem 2, Nr. 2 (02.04.2022): 96–107. http://dx.doi.org/10.3390/physchem2020007.
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This paper analyzes how special relativity changes the equation for the many-body-induced current density starting from the Foldy–Wouthuysen diagonalization of the Dirac–Coulomb Hamiltonian. This current density differs from that obtained with the Gordon decomposition due to the presence of a spin-orbit coupling contribution not considered before for many-body molecular systems. This contribution diverges on atomic nuclei due to the nature of the point charges considered in the nonrelativistic approach, demonstrating that conventionally used nonrelativistic methods are not suitable for dealing with spin effects such as spin-orbit coupling or effects smaller than α2, with α the fine structure constant, and that a fully relativistic approach with a finite charge should be used. Despite the singularity, the spin-orbit coupling current becomes an important contribution to the total current in open-shell systems with high-spin multiplicity and a high atomic number in the nuclear proximity. On long ranges, this contribution is overcome by the Coulomb potential and the derived electric field which decays very quickly for small distances from nuclear charges. An evaluation of this spin-orbit current has been performed in the linear response approach at the HF/DFT level of theory.
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Schaefer, Ted, Glenn H. Penner, Craig Takeuchi und Potlaki Tseki. „Remarks on the internal motion in diphenyl ether. Fluorophenyl ethers“. Canadian Journal of Chemistry 66, Nr. 7 (01.07.1988): 1647–50. http://dx.doi.org/10.1139/v88-267.
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The 13C nuclear magnetic resonance chemical shifts and the 13C,19F spin–spin coupling constants are reported for 4,4′-difluorophenyl ether and 4-fluorophenyl phenyl ether in CS2 and in acetone-d6 solutions. An estimate of 6J90, the extremum in the σ–π coupling constant between the 19F nucleus on one ring and the ipso13C nucleus on the other, is obtained from measurements on 2,6-dibromo-4-fluorophenyl phenyl ether. The ensuing estimates of [Formula: see text], the expectation values of sin2 θ as obtained from 6J(13C,19F), are compared with those obtained from STO-3G MO computations for diphenyl ether and its 4-fluoro derivatives. These computations give conformational energies at 30° intervals of the angles of twist about the two C—O bonds. In rough agreement with C-INDO computations, interconversion of the helical forms is calculated to occur most easily by the so-called one-ring flip mechanism; the barrier to interconversion is less than 1 kJ/mol in the ether and its 4-fluoro derivatives. It appears that the conformational behaviour of these derivatives is unaltered by passage from CS2 to acetone solutions at 300 K. Furthermore, [Formula: see text] values from 6J(13C,I9F) in solution are very similar to those obtained from the computations on the free molecules. If this agreement is not accidental, then it may arise from a high degree of flexibility of the molecules in which, by a disrotatory or one-ring flip mechanism requiring a very low energy of activation, one helical or C2 conformation can be converted to another. The other conformations have considerably higher energies and the solvents do not appear to lower these energies enough to favor their populations significantly at 300 K.
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GUPTA, V., R. HUERTA und G. SÁNCHEZ-COLÓN. „SEMILEPTONIC DECAYS, MAGNETIC MOMENTS AND SPIN DISTRIBUTIONS OF SPIN-1/2 BARYONS WITH SEA CONTRIBUTION“. International Journal of Modern Physics A 13, Nr. 24 (30.09.1998): 4195–212. http://dx.doi.org/10.1142/s0217751x98001992.
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Spin-1/2 baryons are considered as a composite system made out of a "core" of three-quarks surrounded by a "sea" (of gluons and [Formula: see text]-pairs) which is specified by its total quantum numbers. Specifically, we assume this sea to be a flavor octet with spin-0 or 1 but no color. We show our model can provide very good fits to magnetic moments and semileptonic decay data using experimental errors. The predictions for spin distributions are in reasonable agreement with experiment.
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BUNCE, G. „RHIC ACCELERATOR ADVANCES FOR SPIN“. International Journal of Modern Physics A 18, Nr. 08 (30.03.2003): 1255–61. http://dx.doi.org/10.1142/s0217751x03014587.
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Spin physics has always had tight coupling between the physics, both experiment and theory, and accelerator physics. We have all benefited from the tradition of this close collaboration. This workshop is focused on physics issues, and this talk discusses recent advances in the accelerator/polarimetry areas for the RHIC spin program. The first polarized proton collisions at RHIC (and in the world) are planned for this winter. (Since the writing occurs near the end of this first run with polarized proton collisions, our instant analysis of this very successful run is included in this written version.)
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Seredyuk, Maksym, Ana B. Gaspar, Joachim Kusz, Gabriela Bednarek und Philipp Gütlich. „Variable-temperature X-ray crystal structure determinations of {Fe[tren(6-Mepy)3]}(ClO4)2and {Zn[tren(6-Mepy)3]}(ClO4)2compounds: correlation of the structural data with magnetic and Mössbauer spectroscopy data“. Journal of Applied Crystallography 40, Nr. 6 (10.11.2007): 1135–45. http://dx.doi.org/10.1107/s0021889807048571.
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Variable-temperature X-ray crystal structure determinations (80–330 K) on compounds {Fe[tren(6-Mepy)3]}(ClO4)2(1-Fe) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} and {Zn[tren(6-Mepy)3]}(ClO4)2(1-Zn) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} were carried out together with a detailed analysis of the unit-cell volume and parameters in the spin transition region for (1-Fe). Both compounds crystallize in the monoclinic system and retained the space groupP21/cat all measured temperatures. The Fe and Zn atoms are surrounded by six N atoms belonging to imine groups and pyridine groups of the trifurcated ligand, adopting a pseudo-octahedral symmetry. The average Fe—N bond lengths of 2.013 (1) Å (80 K) and 2.216 (2) Å (330 K) are consistent with a low-spin (LS) and a high-spin (HS) state for the iron(II) ions. In contrast to (1-Fe), the structures of (1-Zn) at low and high temperatures are similar and repeat the structural features of the high-spin structure of (1-Fe). The volume of the unit cell increases on heating from 80 to 330 K for (1-Fe) and (1-Zn). On the other hand, while thea,bandccell parameters increase for (1-Fe), they show less variation for (1-Zn). For (1-Fe), variation of the unit-cell volume with temperature recalculated per Fe atom shows a change ΔV= 27.16 Å3during the spin crossover process. Magnetic susceptibility and Mössbauer spectroscopy studies performed on (1-Fe) reveal an inversion temperature,T1/2of 233 K, where the molar fractions of LS and HS sites are both equal to 0.5. The variation in metal–ligand bond lengths, the distortion parameters and the cell parameters are very close to the character of the magnetic curve and the curve of γHS(the molar fraction of HS molecules) derived from the Mössbauer data; this result shows the correlation between structure and physical properties in (1-Fe).
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Bravar, A., I. Alekseev, G. Bunce, S. Dhawan, R. Gill, H. Huang, W. Haeberli et al. „Spin Dependence in Polarized and Elastic Scattering at Very Low Momentum Transfer t at RHIC“. Nuclear Physics B - Proceedings Supplements 146 (September 2005): 77–81. http://dx.doi.org/10.1016/j.nuclphysbps.2005.02.066.
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Komosinska-Vassev, Katarzyna, Paweł Olczyk, Janusz Kasperczyk, Barbara Pilawa, Ryszard Krzyminiewski, Bernadeta Dobosz, Paweł Ramos et al. „EPR Spectroscopic Examination of Different Types of Paramagnetic Centers in the Blood in the Course of Burn Healing“. Oxidative Medicine and Cellular Longevity 2019 (19.06.2019): 1–8. http://dx.doi.org/10.1155/2019/7506274.
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The multicomponent electron paramagnetic resonance spectra of the blood during healing of skin burned wounds treated with a new generation biodegradable dressings containing poly(lactide-co-glycolide) were analysed. The evolution of different types of paramagnetic centers in the blood with time of healing was determined. The EPR spectra of the blood samples at 230 K temperature were measured at 1, 10, and 21 days after burning of the pig skin. The EPR lines of the following paramagnetic centers: the high-spin Fe3+ in methemoglobin (line I), high-spin Fe3+ in transferrin (line II), and Cu2+ in ceruloplasmin and free radicals (line III) were observed in the X-band (9.3 GHz) spectra of the blood. The multicomponent structure of the EPR spectra of the tested blood samples depended on the time of the healing of the burned wounds. The amount of the high-spin Fe3+ in methemoglobin (line I) in the blood decreased after 21 days of the healing of the burned wounds. The amount of the high-spin Fe3+ in transferrin (line II) slightly increased after 21 days of therapy with the basis. The amount of Cu2+ in ceruloplasmin and free radicals (line III) in the blood was very high after 10 days of therapy. At the first day of the healing of the burned wounds, the highest amount of the high-spin Fe3+ in methemoglobin (line I), the relatively lower amounts of the high-spin Fe3+ in transferrin (line II), and Cu2+ in ceruloplasmin and free radicals (line III) existed in the blood. In the medium phase (after 10 days) of the healing of the burned wounds, the extremely higher amounts of Cu2+ in ceruloplasmin and free radicals (line III) appeared in the blood. In the last phase (after 21 days), only the low differences between the amounts of the high-spin Fe3+ in methemoglobin (line I), the high-spin Fe3+ in transferrin (line II), and Cu2+ in ceruloplasmin and free radicals (line III) were observed. The present study may serve as a starting point for the development of a new technique for monitoring molecular complexes containing iron Fe3+ (methemoglobin, transferrin) or copper Cu2+ ions (ceruloplasmin) and free radicals in the blood during wound healing.
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Dos Santos, Wagner G., Isabel Pacheco, Ming-Yih Liu, Miguel Teixeira, António V. Xavier und Jean LeGall. „Purification and Characterization of an Iron Superoxide Dismutase and a Catalase from the Sulfate-Reducing BacteriumDesulfovibrio gigas“. Journal of Bacteriology 182, Nr. 3 (01.02.2000): 796–804. http://dx.doi.org/10.1128/jb.182.3.796-804.2000.
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ABSTRACT The iron-containing superoxide dismutase (FeSOD; EC 1.15.1.1 ) and catalase (EC 1.11.1.6 ) enzymes constitutively expressed by the strictly anaerobic bacterium Desulfovibrio gigas were purified and characterized. The FeSOD, isolated as a homodimer of 22-kDa subunits, has a specific activity of 1,900 U/mg and exhibits an electron paramagnetic resonance (EPR) spectrum characteristic of high-spin ferric iron in a rhombically distorted ligand field. Like other FeSODs from different organisms, D. gigas FeSOD is sensitive to H2O2 and azide but not to cyanide. The N-terminal amino acid sequence shows a high degree of homology with other SODs from different sources. On the other hand, D. gigas catalase has an estimated molecular mass of 186 ± 8 kDa, consisting of three subunits of 61 kDa, and shows no peroxidase activity. This enzyme is very sensitive to H2O2and cyanide and only slightly sensitive to sulfide. The native enzyme contains one heme per molecule and exhibits a characteristic high-spin ferric-heme EPR spectrum (g y,x = 6.4, 5.4); it has a specific activity of 4,200 U/mg, which is unusually low for this class of enzyme. The importance of these two enzymes in the context of oxygen utilization by this anaerobic organism is discussed.
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Bonville, P., J. A. Hodges, E. Bertin, J. Ph Bouchaud, P. Dalmas de Réotier, L. P. Regnault, H. M. Rønnow, J. P. Sanchez, S. Sosin und A. Yaouanc. „Transitions and Spin Dynamics at Very Low Temperature in the Pyrochlores Yb2Ti2O7and Gd2Sn2O7“. Hyperfine Interactions 156/157, Nr. 1-4 (2004): 103–11. http://dx.doi.org/10.1023/b:hype.0000043235.21257.13.
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Nayak, Alekha C. „Very special relativity induced phase due to neutrino magnetic moment in neutrino oscillation“. International Journal of Modern Physics A 36, Nr. 13 (05.05.2021): 2150079. http://dx.doi.org/10.1142/s0217751x21500792.
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In Very Special Relativity (VSR), the neutrino mass term is coupled with the VSR preferred axis, and hence Lorentz violating in nature. Beyond standard model physics predicts neutrino magnetic moment which is linearly proportional to the mass eigenstates of the neutrinos. We report an additive kinematic phase in the neutrino flavor oscillation due to the neutrino magnetic moment in the VSR framework. This phase is proportional to the coupling between the VSR preferred axis with the external magnetic field as well as the spin of the neutrino. Furthermore, we predict time variation in the neutrino oscillation with a period of one sidereal day.
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Yue, Huan, Ji Ae Park, Son Long Ho, Mohammad Yaseen Ahmad, Hyunsil Cha, Shuwen Liu, Tirusew Tegafaw et al. „New Class of Efficient T2 Magnetic Resonance Imaging Contrast Agent: Carbon-Coated Paramagnetic Dysprosium Oxide Nanoparticles“. Pharmaceuticals 13, Nr. 10 (15.10.2020): 312. http://dx.doi.org/10.3390/ph13100312.
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Nanoparticles are considered potential candidates for a new class of magnetic resonance imaging (MRI) contrast agents. Negative MRI contrast agents require high magnetic moments. However, if nanoparticles can exclusively induce transverse water proton spin relaxation with negligible induction of longitudinal water proton spin relaxation, they may provide negative contrast MR images despite having low magnetic moments, thus acting as an efficient T2 MRI contrast agent. In this study, carbon-coated paramagnetic dysprosium oxide (DYO@C) nanoparticles (core = DYO = DyxOy; shell = carbon) were synthesized to explore their potential as an efficient T2 MRI contrast agent at 3.0 T MR field. Since the core DYO nanoparticles have an appreciable (but not high) magnetic moment that arises from fast 4f-electrons of Dy(III) (6H15/2), the DYO@C nanoparticles exhibited an appreciable transverse water proton spin relaxivity (r2) with a negligible longitudinal water proton spin relaxivity (r1). Consequently, they acted as a very efficient T2 MRI contrast agent, as proven from negative contrast enhancements seen in the in vivo T2 MR images.
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Abdelsalam, Hazem, Vasil A. Saroka, Mohamed M. Atta, Omar H. Abd-Elkader, Nouf S. Zaghloul und Qinfang Zhang. „Tunable Sensing and Transport Properties of Doped Hexagonal Boron Nitride Quantum Dots for Efficient Gas Sensors“. Crystals 12, Nr. 11 (21.11.2022): 1684. http://dx.doi.org/10.3390/cryst12111684.
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The electronic, sensing, and transport properties of doped square hexagonal boron nitride (shBN) quantum dots were investigated using density functional theory calculations. The electronic and magnetic properties were controlled by substitutional doping. For instance, heterodoping with Si and C atoms decreased the energy gap to half its value and converted the insulator shBN quantum dot to a semiconductor. Doping with a single O atom transformed the dot to spin half metal with a tiny spin-up energy gap and a wide spin-down gap. Moreover, doping and vacancies formed low-energy interactive molecular orbitals which were important for boosting sensing properties. The unmodified shBN quantum dot showed moderate physical adsorption of NO2, acetone, CH4, and ethanol. This adsorption was elevated by doping due to interactions between electrons in the low-energy orbitals from the doped-shBN dot and π-bond electrons from the gas. The transport properties also showed a significant change in the current by doping. For instance, the spin-up current was very high compared to the spin-down current in the shBN dots doped with an O atom, confirming the formation of spin half metal. The spin-up/down currents were strongly affected by gas adsorption, which can be used as an indicator of the sensing process.
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Costes, Jean-Pierre, Arnaud Dupuis und Jean-Pierre Laurent. „A Very-High-Spin Molecule: Preparation, Characterization and Magnetic Properties of an FeIII–GdIII Complex with anS = 12/2 Ground State“. European Journal of Inorganic Chemistry 1998, Nr. 10 (Oktober 1998): 1543–46. http://dx.doi.org/10.1002/(sici)1099-0682(199810)1998:10<1543::aid-ejic1543>3.0.co;2-t.
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Mattauch, Stefan, Alexandros Koutsioubas, Ulrich Rücker, Denis Korolkov, Vicenzo Fracassi, Jos Daemen, Ralf Schmitz et al. „The high-intensity reflectometer of the Jülich Centre for Neutron Science: MARIA“. Journal of Applied Crystallography 51, Nr. 3 (29.05.2018): 646–54. http://dx.doi.org/10.1107/s1600576718006994.
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MARIA (magnetism reflectometer with high incident angle) is a world class vertical sample reflectometer dedicated to the investigation of thin films in the fields of magnetism, soft matter and biology. The elliptical vertically focusing guide allows one to measure small samples with a typical size of 1 × 1 cm very efficiently. The double-bounce polarizer and the in situ pumped 3He SEOP (spin-exchange optical pumping) neutron spin filter cell for analysing the polarization of the reflected neutron beam can be moved into the beam in seconds. The polarized flux of MARIA amounts to 5 × 107 n (s cm2)−1 at the sample position with a horizontally collimated beam of 3 mrad, a wavelength of λ = 4.5 Å and a wavelength resolution of Δλ/λ = 10%. In the non-polarized mode a flux of 1.2 × 108 n (s cm2)−1 is achieved in this configuration. MARIA is also capable of grazing-incidence small-angle neutron scattering measurements, using a pinhole collimation with two four-segment slits and an absorber that prevents the focusing of the elliptical guide in the vertical direction.
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Liu, Li, Shi Jie Xu und Song Zhan Li. „Determination of Reactive Oxygen Species in Cigarette Smoke by DR6G Fluorescent Probe“. Advanced Materials Research 361-363 (Oktober 2011): 1863–67. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.1863.
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A mass of reactive oxygen species(ROS) are produced in the process of smoking. Superfluous ROS can induce the oxidative stress in organism, which will cause irreversible damage to cells. Fluorescent probe is taken as a marker of oxidative stress in biology and has been applied to ROS detection in the field of biology and chemistry for high sensitivity, high simplicity of data collection and high resolution. As one type of fluorescent probe, no-fluorescent dihydrorhodamine 6G(dR6G) will be oxidized to the fluorescent rhodamine 6G. In this process, each molecule reacts with two active oxygen molecules. The probe can be used to detect ROS in mainstream cigarette smoke by using derivative fluorescence method. The action mechanism of ROS on dR6G was investigated and the standard curve of R6G fluorescence intensity with its content was built up. The contents of ROS from the 4 types of cigarettes purchased in market were detected and the cleaning ability of filter tip to ROS in cigarette smoke was also researched. The result shows that the amount of ROS has close relationship with the types of tobacco and cigarette production technology and the cleaning ability of filter tip to ROS in cigarette smoke is very limited. Compared with other detecting methods such as electronic spin resonance(ESR), chromatography and mass spectrometry, this detection method by the fluorescent probe has higher efficiency and sensitivity and will have wide applications in the ROS detection fields.