An original technique for describing excited states of electrons in crystal structure has been considered by an example of lithium. It is shown that the electron spectrum in lithium changes only ...slightly at large values of lattice parameter (up to 8.77 Bohr radii). The lifetimes of excited electrons of external
s
and
p
states differ significantly at lattice parameters
d
< 8.77 Bohr radii. A metastable crystalline state of bcc lithium is found, which barely depends on the excitation power at a lattice constant equal to 6.55 Bohr radii, corresponding to the bcc lattice constant of lithium in the ground state.
Recent results from a search for multi-quark exotic states at D0 experiment (FNAL, USA) are presented. This includes the new data for possible tetraquark state X(5568) decaying to Bs0π±, in the ...channels with semileptonic decays of Bs0 mesons. Also, result from the J/ψπ system analysis and an evidence for exotic charged charmoniumlike state Zc(3900) in semiinclusive weak decays of B-flavored hadrons are presented as well.
Metal–cage and intracluster bonding was studied in detail by quantum theory of atoms in molecules (QTAIM) for the four major classes of endohedral metallofullerenes (EMFs), including ...monometallofullerenes Ca@C72, La@C72, M@C82 (M=Ca, Sc, Y, La), dimetallofullerenes Sc2@C76, Y2@C82, Y2@C79N, La2@C78, La2@C80, metal nitride clusterfullerenes Sc3N@C2n (2n=68, 70, 78, 80), Y3N@C2n (2n=78, 80, 82, 84, 86, 88), La3N@C2n (2n=88, 92, 96), metal carbide clusterfullerenes Sc2C2@C68, Sc2C2@C82, Sc2C2@C84, Ti2C2@C78, Y2C2@C82, Sc3C2@C80, as well as Sc3CH@C80 and Sc4Ox@C80 (x=2, 3), that is, 42 EMF molecules and ions in total. Analysis of the delocalization indices and bond critical point (BCP) indicators such as Gbcp/ρbcp, Hbcp/ρbcp, and |Vbcp|/Gbcp, revealed that all types of bonding in EMFs exhibit a high degree of covalency, and the ionic model is reasonable only for the Ca‐based EMFs. Metal–metal bonds with negative values of the electron‐density Laplacian were found in Y2@C82, Y2@C79N, Sc4O2@C80, and anionic forms of La2@C80. A delocalized nature of the metal–cage bonding results in a topological instability of the electron density in EMFs with an unpredictable number of metal–cage bond paths and large elipticity values.
Metal–cage and intracluster bonding in endohedral metallofullerenes (EMFs), including mono‐ and dimetallofullerenes; metal carbide, nitride, and oxide clusterfullerenes; and Sc3CH§C80, was studied by quantum theory of atoms in molecules. The picture shows for La2§C78 a molecular graph in the vicinity of the La atoms (bond critical point (CP) red, ring CP yellow, cage CP green).
Shallow and deep trap levels in X-ray irradiated β-Ga2O3: Mg Luchechko, A.; Vasyltsiv, V.; Kostyk, L. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
02/2019, Letnik:
441
Journal Article
Recenzirano
The results of the investigation of thermostimulated luminescence (TSL) and photoconductivity (PC) of the X-ray irradiated undoped and Mg2+ doped β-Ga2O3 single crystals are presented. Three ...low-temperature peaks at 116 K, 147 K and 165 K are observed on the TSL glow curves of undoped crystals. The high-temperature TSL peaks at 354 K and 385 K are dominant in Mg2+ doped crystals. The correlation between doping with Mg2+ ions and the local energy levels of the intrinsic structural defects of β-Ga2O3, which are responsible for the TSL peaks and PC, is established. The nature of TSL peaks and the appropriate photoconductivity excitation bands are discussed.
Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar ...structures, stabilized by localized two-center-two-electron (2c-2e) σ bonds on the periphery and delocalized multicenter-two-electron (nc-2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron's electron deficiency and leads to fluxional behavior, which has been observed in B13(+) and B19(-). A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiation has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B(-), formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B(-)/C analogy. It is believed that the electronic transmutation concept will be effective and valuable in aiding the design of new boride materials with predictable properties. The study of boron clusters with intermediate properties between those of individual atoms and bulk solids has given rise to a unique opportunity to broaden the frontier of boron chemistry. Understanding boron clusters has spurred experimentalists and theoreticians to find new boron-based nanomaterials, such as boron fullerenes, nanotubes, two-dimensional boron, and new compounds containing boron clusters as building blocks. Here, a brief and timely overview is presented addressing the recent progress made on boron clusters and the approaches used in the authors' laboratories to determine the structure, stability, and chemical bonding of size-selected boron clusters by joint photoelectron spectroscopy and theoretical studies. Specifically, key findings on all-boron hydrocarbon analogues, metal-centered boron wheels, and electronic transmutation in boron clusters are summarized.
Three unprecedented helical nanographenes (1, 2, and 3) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X‐ray crystallographic analysis. ...The embedded azulene unit in 2 possesses a record‐high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis‐spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps (2: 1.88 eV; 3: 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in‐situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties.
An odd contribution: Azulene‐embedded helical nanographenes with global aromaticity are synthesized by a Scholl‐type cyclization. X‐ray crystallographic analysis clearly reveals the formation of an azulene unit in the helical π‐system. The embedded azulene core adopts a highly twisted conformation and is less aromatic than pristine azulene.
In this study we report the results of first principle quantum chemical modeling of electronic structure and spatial configuration of LaF3 crystal containing the F-center. Theoretical predictions of ...atomic and electronic properties of LaF3 are given by means of density functional theory. From our modeling we predict that the F-center placed at fluorine ion position between the lanthanum planes at tysonite LaF3 is the most energetically stable. In order to interpret the structure of the optical absorption spectrum of X-irradiated LaF3 we performed calculations of excited and transition states of the F-center within the embedded cluster formalism using time dependent density functional theory. Predicted transition energies and oscillator strengths of LaF3 containing the F-center are in line with those recently measured.