| 1. |
- de Groot, Frank M. F., et al.
(författare)
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2p x-ray absorption spectroscopy of 3d transition metal systems
- 2021
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 249
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Tidskriftsartikel (refereegranskat)abstract
- This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.
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| 2. |
- Fronzoni, Giovanna, et al.
(författare)
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Vibrationally resolved high-resolution NEXAFS and XPS spectra of phenanthrene and coronene
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:4, s. 044313-
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Tidskriftsartikel (refereegranskat)abstract
- We performed a combined experimental and theoretical study of the C1s Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy and X-ray Photoelectron Spectroscopy in the gas phase of two polycyclic aromatic hydrocarbons (phenanthrene and coronene), typically formed in combustion reactions. In the NEXAFS of both molecules, a double-peak structure appears in the C1s -> LUMO region, which differ by less than 1 eV in transition energies. The vibronic coupling is found to play an important role in such systems. It leads to weakening of the lower-energy peak and strengthening of the higher-energy one because the 0 - n (n > 0) vibrational progressions of the lower-energy peak appear in nearly the same region of the higher-energy peak. Vibrationally resolved theoretical spectra computed within the Frank-Condon (FC) approximation and linear coupling model agree well with the high-resolution experimental results. We find that FC-active normal modes all correspond to in-plane vibrations.
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| 3. |
- Guarnaccio, Ambra, et al.
(författare)
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PPT Isolated Molecule and Its Building Block Moieties Studied by C 1s and O 1s Gas Phase X-ray Photoelectron and Photoabsorption Spectroscopies
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:18, s. 9774-9786
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Tidskriftsartikel (refereegranskat)abstract
- The present study is focused on the comprehensive gas phase electronic structure characterization of 2,8-bis-(diphenylphosphoryl)-dibenzo[b,d]thiophene (PPT), a promising ambipolar phosphorescent host material recently introduced in organic light-emitting diodes (OLEDs). This molecular system can be considered ideally formed by two diphenylphosphine oxide (dPPO) moieties functionalizing the small dibenzothiophene (DBT) core. PPT is characterized by high triplet energy and is known as good vacuum sublimable electron transporting material for blue OLEDs. The triphenyl phosphine oxide (TPPO) molecule has been chosen as the model compound of the dPPO groups in PPT. A combined experimental and theoretical study by density functional theory of the gas phase electronic structure of TPPO and PPT has been performed through X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy measured at the carbon and oxygen is regions. The study represents a detailed characterization of the impact of the single building blocks on the electronic structure of the whole PPT molecule. Moreover, it confirms that the phosphine oxide groups act as breaking points of the pi-conjugation between the DBT core of PPT and the outer groups, leaving the electronic structures of the compound practically matching those of the central DBT moiety.
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| 4. |
- Hua, Weijie, et al.
(författare)
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Fe L-Edge X-ray Absorption Spectra of Fe(II) Polypyridyl Spin Crossover Complexes from Time-Dependent Density Functional Theory
- 2013
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 117:51, s. 14075-14085
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Tidskriftsartikel (refereegranskat)abstract
- L-edge near-edge X-ray fine structure spectroscopy (NEXAFS) has become a powerful tool to study the electronic structure and dynamics of metallo-organic and biological compounds in solution. Here, we present a series of density functional theory calculations of Fe L-edge NEXAFS for spin crossover (SCO) complexes within the time-dependent framework. Several key factors that control the L-edge excitations have been carefully examined using an Fe(II) polypyridyl complex [Fe(tren(py)(3))](2+) (where tren(py)(3) = tris(2-pyridylmethyliminoethyl)amine) as a model system. It is found that the electronic spectra of the low-spin (LS, singlet), intermediate-spin (IS, triplet), and high-spin (HS, quintet) states have distinct profiles. The relative energy positions, but not the spectral profiles, of different spin states are sensitive to the choice of the functionals. The inclusion of the vibronic coupling leads to almost no visible change in the resulting NEXAFS spectra because it is governed only by low-frequency modes of less than 500 cm(-1). With the help of the molecular dynamics sampling in acetonitrile at 300 K, our calculations reveal that the thermal motion can lead to a noticeable broadening of the spectra. The main peak position is strongly associated with the length of the Fe-N bond.
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