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RISS 인기검색어
- 검색키워드
- 저자 : Doumy, Gilles (검색결과 5 건)
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Ross, Matthew,Andersen, Amity,Fox, Zachary W.,Zhang, Yu,Hong, Kiryong,Lee, Jae-Hyuk,Cordones, Amy,March, Anne Marie,Doumy, Gilles,Southworth, Stephen H.,Marcus, Matthew A.,Schoenlein, Robert W.,Mukame American Chemical Society 2018 The journal of physical chemistry. B, Condensed ma Vol.122 No.19
<P>We present a joint experimental and computational study of the hexacyanoferrate aqueous complexes at equilibrium in the 250 meV to 7.15 keV regime. The experiments and the computations include the vibrational spectroscopy of the cyanide ligands, the valence electronic absorption spectra, and Fe 1s core hole spectra using element-specific-resonant X-ray absorption and emission techniques. Density functional theory-based quantum mechanics/molecular mechanics molecular dynamics simulations are performed to generate explicit solute-solvent configurations, which serve as inputs for the spectroscopy calculations of the experiments spanning the IR to X-ray wavelengths. The spectroscopy simulations are performed at the same level of theory across this large energy window, which allows for a systematic comparison of the effects of explicit solute-solvent interactions in the vibrational, valence electronic, and core-level spectra of hexacyanoferrate complexes in water. Although the spectroscopy of hexacyanoferrate complexes in solution has been the subject of several studies, most of the previous works have focused on a narrow energy window and have not accounted for explicit solute-solvent interactions in their spectroscopy simulations. In this work, we focus our analysis on identifying how the local solvation environment around the hexacyanoferrate complexes influences the intensity and line shape of specific spectroscopic features in the UV/vis, X-ray absorption, and valence-to-core X-ray emission spectra. The identification of these features and their relationship to solute-solvent interactions is important because hexacyanoferrate complexes serve as model systems for understanding the photochemistry and photophysics of a large class of Fe(II) and Fe(III) complexes in solution.</P> [FIG OMISSION]</BR>
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Britz, Alexander,Gawelda, Wojciech,Assefa, Tadesse A.,Jamula, Lindsey L.,Yarranton, Jonathan T.,Galler, Andreas,Khakhulin, Dmitry,Diez, Michael,Harder, Manuel,Doumy, Gilles,March, Anne Marie,Bajno American Chemical Society 2019 Inorganic chemistry Vol.58 No.14
<P>We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)<SUB>2</SUB>]<SUP>2+</SUP> (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the <SUP>5</SUP>T<SUB>2</SUB>/<SUP>3</SUP>T<SUB>1</SUB> crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kβ X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the <SUP>5</SUP>T<SUB>2</SUB> state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of ∼0.18 Å for a <SUP>5</SUP>T<SUB>2</SUB> state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited <SUP>5</SUP>T<SUB>2</SUB> state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin <SUP>1</SUP>A<SUB>1</SUB> ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.</P><P>Time-resolved X-ray emission and absorption spectroscopies have been used to probe the excited-state electronic and geometric structure of an Fe(II) polypyridyl complex. Analysis of the data revealed that the lowest energy excited state is high-spin (<I>S</I> = 2) in character. This determination had not been possible using other experimental techniques (e.g., time-resolved optical spectroscopy), demonstrating the potential for ultrafast X-ray methods to address scientific questions that are difficult to resolve by other means.</P> [FIG OMISSION]</BR>
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Mohammed Belkheir,Mohamed Alami,Allel Mokaddem,Bendouma Doumi,Ahmed Boutaous 한국섬유공학회 2022 Fibers and polymers Vol.23 No.10
Compared to Silica Optical Fibers, Polymethyl Methacrylate Polymer Optical Fibers (POFs) present a highattenuation and dispersion properties for long distances. However, they have more benefits in terms of mechanical andthermal characteristics such as viscoelasticity, strain and bending that allow them to be widely used for various life domainslike biomedical and sensing applications. This paper studies and analyzes the effect of humidity on the fiber-matrix interfacedamage for composite materials based on (Topas/PMMA, Topas-Zeonex/PMMA and Zeonex/PMMA) using geneticapproach based on Weibull probabilistic formalism and the law of diffusion. The results gained show that the mechanicalstresses applied to the three composite materials provoke damage to the interface with different levels, lower for Topas/PMMA, medium for Topas-Zeonex/PMMA and higher for Zeonex/PMMA. In the other hand, the fiber-matrix interface ofTopas/PMMA composite is not influenced by humidity compared to other interfaces of Topas-Zeonex/PMMA and Zeonex/PMMA composite materials. Our present results are closely similar to those found by Leal et al.
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S. Amari,F. Dahmane,S. Bin Omran,B. Doumi,I. E. Yahiaoui,A. Tadjer,R. Khenata 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.9
In this study, the structural, magnetic and electronic properties of the Co2FeGe1−xSix (x = 0, 0.5, 1) Heusler compounds have been calculated using the full-potential linearized augmented plane-wave method based on the spin density functional theory within the generalized gradient approximation of Perdew-Burke-Ernzerhof. In order to take into account the correlation effects, we have also performed GGA + U calculations, where the Hubbard on-site Coulomb interaction correction U is calculated by using the constraint local density approximation for the Co and the Mn atoms. The Cu2MnAl-type structure is found to be energetically more favorable than the Hg2CuTitype structure for both the Co2FeSi and the Co2FeGe compounds. The calculated atomic resolved densities of states of Co2FeSi and Co2FeGe indicate nearly half-metallic behaviors with small spindown electronic densities of states at the Fermi level. This behavior is corrected by including the Hubbard Coulomb energy U term. The Coulomb exchange correlation U confirms the halfmetallic property in both the Co2FeSi and the Co2FeGe compounds. We also discuss the electronic structures, the total and the partial densities of states, and the local magnetic moments. The Co2FeGe0.5Si0.5 compound shows a nearly half-metallic behavior with a small spin-down electronic density of states at the Fermi level in both the GGA and GGA+U approximations.
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