Document Details
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Document Type |
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Thesis |
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Document Title |
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SOFT X-RAY SPECTROSCOPY OF TRANSITION METAL COMPOUNDS: A THEORETICAL PERSPECTIVE أطياف أشعة إكس منخفضة الطاقة لمركبات العناصر الانتقالية: رؤية نظرية |
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Subject |
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faculty of science |
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Document Language |
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Arabic |
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Abstract |
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The aim of this study is to identify and develop an efficient and versatile theoretical methodology for the treatment of soft X-ray spectra of transition metal complexes. It enables us to quantify the L-edge excitations of electrons from the core 2p core to the unoccupied 3d orbitals. These excitations avail information on the nature of metal−ligand interaction. To achieve this goal, detailed electronic structure theory simulations have been carried out to establish persuasive interpretations of transition metals electronic structures. X-ray absorption (XAS) and resonant inelastic scattering (RIXS) of some selected cobalt complexes were studied theoretically using the restricted active space self-consistent field (RASSCF) and restricted active space state interaction (RASSI) approaches. The effect of basis set, ligand field structure, ligand field strength, and metal charge have been examined to validate the theoretical model adopted throughout the work. Restricted active space second order perturbation theory (RASPT2) has been used to computed and investigate the effect of the dynamic correlation correction on the spectra. Inclusively, L-edge transition states have been studied throughout X- ray absorption spectra, two-dimensional RIXS spectra, and spin-orbit coupled wave functions.
Focusing on the identification of cobalt complexes, the spectral signatures of [Co(H2O)6]2+ were investigated as a reference complex. Accordingly, different chlorinated species in octahedral, [Co(H2O)6-xClx](2-x)+, and tetrahedral, [Co(H2O)4-xClx](2-x)+, coordinations were studied to explore the effect of ligand field structure in addition to (Cl-) concentration in ligand field coordination. The XAS and RIXS results confirm that the best agreement is obtained for the hexa-aqua complex [Co(H2O)6]2+. Concerning the methodological techniques, the basis set convergence shows more feasibility for VTZ and VQZ more than VDZ. This is because the double zeta basis set yields a limitation on the L3 band features. In the same field, the RASPT2 correction for dynamical correlation confirms a clear improvement of the agreement with experiment in the more structured L3 band. For all complexes, L2 band shows a weak structure, while L3 band exhibits more prominent features. The spectra of chlorine-containing complexes were quite similar but deviated substantially from those of the [Co(H2O)6]2+ complex. They were affected by the spin-orbit coupling (SOC) more than by the weak Cl- ligand substitutions. The assignment of spectra have been discussed according to the occupation of 3d (t2g, eg) and 3d (t2,e) for the octahedral and tetrahedral complexes, respectively.
Additionally, ligand field strength has been investigated via comparing the reference complex with [Co(CN)6]4-. In order to get a much better insight into this part, an additional case study has been added ([Co(CN)6]4-/3-). In both cases there is considerable differences in X-ray and RIXS spectra. The inconsistencies in these observations were due to the difference of the ground state electron configurations between the two cases (d7 (t2g5 eg2) for Co2+ and d6 (t2g6 eg0) for Co3+). It is clear that Co2+ has an open shell (paramagnetic) electron configuration, while Co3+ has is a closed shell (diamagnetic) distribution. |
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Supervisor |
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Prof. Saadullah G. Aziz |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1441 AH
2020 AD |
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Co-Supervisor |
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Dr. Walid I. Hassan |
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Added Date |
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Monday, June 22, 2020 |
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Researchers
| بسمة حمدان اللحياني | Allehyani, Basmah Hamdan | Researcher | Doctorate | |
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