Electronic relaxation and the theory of chemical shifts of X-ray characteristic lines

ABSTRACTAt present, crystalline ceramic based on titanate pyrochlore, (Ca,Gd,Hf,Pu,U)2Ti2O7, is considered as the US candidate waste form for the immobilization of weapons grade plutonium. Naturally occuring U-bearing minerals with pyrochlore-type structure: hatchettolite, betafite, and ellsworthite, were studied in orders to understand long-term radiation damage effects in Pu ceramic waste forms. Chemical shifts (δ) of U(Lδ1)– and U(Lβ1) – X-ray emission lines were measured by X-ray spectrometry. Calculations were performed on the basis of a two-dimensional δLá1- and δLδ1- correlation diagram. It was shown that 100% of uranium in hatchettolite and, probably, 95-100% of uranium in betafite are in the form of (UO2)2+. formal calculation shows that in ellsworthite only 20% of uranium is in the form of U4+ and 80% of the rest is in the forms of U5+ and U6+. The conversion of the initial U4+ ion originally occurring in the pyrochlore structure of natural minerals to (UO2)2+ due to metamict decay causes a significant increase in uranium mobility.

Download Full-text

Characterization of Charge States in Conducting Organic Nanoparticles by X-ray Photoemission Spectroscopy

Materials ◽

10.3390/ma14082058 ◽

2021 ◽

Vol 14 (8) ◽

pp. 2058

Author(s):

Jordi Fraxedas ◽

Antje Vollmer ◽

Norbert Koch ◽

Dominique de Caro ◽

Kane Jacob ◽

...

Keyword(s):

Partial Oxidation ◽

Chemical Shifts ◽

Large Family ◽

Photoemission Spectroscopy ◽

Intrinsic Structure ◽

X Ray ◽

Level Lines ◽

Donor And Acceptor ◽

Electronic Configurations

The metallic and semiconducting character of a large family of organic materials based on the electron donor molecule tetrathiafulvalene (TTF) is rooted in the partial oxidation (charge transfer or mixed valency) of TTF derivatives leading to partially filled molecular orbital-based electronic bands. The intrinsic structure of such complexes, with segregated donor and acceptor molecular chains or planes, leads to anisotropic electronic properties (quasi one-dimensional or two-dimensional) and morphology (needle-like or platelet-like crystals). Recently, such materials have been synthesized as nanoparticles by intentionally frustrating the intrinsic anisotropic growth. X-ray photoemission spectroscopy (XPS) has emerged as a valuable technique to characterize the transfer of charge due to its ability to discriminate the different chemical environments or electronic configurations manifested by chemical shifts of core level lines in high-resolution spectra. Since the photoemission process is inherently fast (well below the femtosecond time scale), dynamic processes can be efficiently explored. We determine here the fingerprint of partial oxidation on the photoemission lines of nanoparticles of selected TTF-based conductors.

Download Full-text

X-ray transient absorption reveals the 1Au (nπ*) state of pyrazine in electronic relaxation

Nature Communications ◽

10.1038/s41467-021-25045-0 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Valeriu Scutelnic ◽

Shota Tsuru ◽

Mátyás Pápai ◽

Zheyue Yang ◽

Michael Epshtein ◽

...

Keyword(s):

Electronic Excitation ◽

Transient Absorption ◽

Transient Absorption Spectroscopy ◽

Electronic Relaxation ◽

Nonadiabatic Dynamics ◽

X Ray ◽

Organic Chromophores ◽

Dynamics Simulations ◽

X Ray Absorption ◽

Structure Calculations

AbstractElectronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized 1B2u (ππ*) (S2) and 1B3u (nπ*) (S1) states, the participation of the optically dark 1Au (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computations. Despite 1Au (nπ*) and 1B3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The 1Au (nπ*) state is populated in 200 ± 50 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.

Download Full-text

Physical genetics: Cross-breeding density functional theory and X-ray photoelectron spectroscopy to rationalize chemical shifts of binding energies in solid compounds

Solid State Sciences ◽

10.1016/j.solidstatesciences.2020.106359 ◽

2020 ◽

Vol 110 ◽

pp. 106359

Author(s):

Horst P. Beck ◽

Giuliano Moretti

Keyword(s):

Density Functional Theory ◽

Photoelectron Spectroscopy ◽

Density Functional ◽

Chemical Shifts ◽

Binding Energies ◽

Breeding Density ◽

Functional Theory ◽

X Ray ◽

Cross Breeding ◽

Solid Compounds

Download Full-text

History and Cross-Disciplinary Perspective of Compositional Imaging and Mapping With Nexafs Microscopy

Microscopy and Microanalysis ◽

10.1017/s1431927600020894 ◽

1998 ◽

Vol 4 (S2) ◽

pp. 154-155

Author(s):

H. Ade

Keyword(s):

Electronic Structures ◽

Chemical Shifts ◽

Electronic States ◽

Inorganic Materials ◽

Chemical Bonds ◽

Fundamental Physics ◽

X Ray ◽

Disciplinary Perspective ◽

Core Electrons ◽

X Ray Absorption

In Near Edge X-ray Absorption Fine Structure (NEXAFS) microscopy, excitations of core electrons into unoccupied molecular orbitals or electronic states provide sensitivity to a wide variety of chemical functionalities in molecules and solids. This sensitivity complements infrared (IR) spectroscopy, although the NEXAFS spectra are not quite as specific and “rich” as IR spectra. The sensitivity of NEXAFS to distinguish chemical bonds and electronic structures covers a wide variety of samples: from metals to inorganics and organics. (There is a tendency in the community to use the term NEXAFS for soft x-ray spectroscopy of organic materials, while for inorganic materials or at higher energies X-ray Absorption Near Edge Spectroscopy (XANES) is utilized, even though the fundamental physics is the same.) The sensitivity of NEXAFS is particularly high to distinguish saturated from unsaturated bonds. NEXAFS can also detect conjugation in a molecule, as well as chemical shifts due to heteroatoms.

Download Full-text

New insights about the hostguest chemistry of the tungsten oxo complex of calix[4]arene, and novel "one pot" difunctionalizations of calix[4]arene using tetrachlorometal(VI) oxide (M = Mo, W)

Canadian Journal of Chemistry ◽

10.1139/v04-097 ◽

2004 ◽

Vol 82 (10) ◽

pp. 1452-1461 ◽

Cited By ~ 9

Author(s):

Pascal Mongrain ◽

Jasmin Douville ◽

Jonathan Gagnon ◽

Marc Drouin ◽

Andreas Decken ◽

...

Keyword(s):

Water Molecule ◽

Lewis Acid ◽

Chemical Shifts ◽

Strong Interactions ◽

Ir Absorption ◽

One Pot ◽

X Ray ◽

Strong Lewis Acid ◽

Successful Removal ◽

Coordinated Water

The strong Lewis acid tungsten oxo complex of calix[4]arene can be obtained in both hydrated and non-hydrated forms. This complex coordinates a water molecule inside the cavity via strong O···W interactions with relatively short distances of 2.284(4) and 2.329(2) Å for the tungsten oxo complex of calix[4]arene··H2O·aniline (1), and the tungsten oxo complex of calix[4]arene·H2O·toluene (2·toluene), respectively. The strong interactions are also deduced by the relatively high H2O elimination temperature observed by TGA and DSC (above 200 °C). The coordinated water molecule inside the calix[4]arene cavity is characterized by a strong IR absorption at 3616 cm1, and a narrow resonance at ~1.2 ppm (the chemical shifts of the uncoordinated water are 1.55 and 1.60 ppm in C6D6 and CDCl3, respectively). This water molecule gives rise to H-bonds with aniline in 1. The tungsten oxo complex of 5,11,17,23-tetrabromocalix[4]arene (4), also binds H2O as the characteristic signatures are observed. The successful removal of H2O in 2, is performed under mild conditions using bis(tetrahydrofuran)-uranyl nitrate as a competitive Lewis acid. When this reaction is performed in acetonitrile, butyronitrile or tert-butylnitrile, the corresponding tungsten oxo complexes of calix[4]arene·acetonitrile (3), ·butyronitrile (5), and ·tert-butylnitrile (6) are obtained. The use of uranyl as a H2O abstractor is unprecedented. The X-ray structure of 3 consists of a tungsten oxo complex of calix[4]arene coordinated by an acetonitrile molecule (d(W···N = 2.412(2) Å). The tetra-5,11,17,23-choromethyl-25,26,27,28-tetrahydroxycalix[4]arene reacts with M(O)Cl4 (M = Mo, W) in a 1:1 stoichiometry, via a tetra FriedelCrafts addition of benzene or toluene, followed by a lower-rim complexation of the metal oxide, to form "flower-shaped" calix[4]arenes. This "one pot" double functionalization is unprecedented.Key words: calix[4]arene, tungsten, molybdenum, X-ray, hostguest, FriedelCrafts, Lewis acid, uranyl, DSC, TGA.

Download Full-text

SCF Xα SW calculations of chemical shifts of X-ray and electron emission lines and relaxation properties of SiX4 molecules

Chemical Physics Letters ◽

10.1016/0009-2614(79)80095-0 ◽

1979 ◽

Vol 68 (1) ◽

pp. 175-178 ◽

Cited By ~ 20

Author(s):

E. Hartmann ◽

R. Szargan

Keyword(s):

Electron Emission ◽

Chemical Shifts ◽

Emission Lines ◽

Relaxation Properties ◽

X Ray

Download Full-text

Electronic relaxation and the theory of chemical shifts of X-ray characteristic lines