σ Bonds: Electronic structure, photophysics, and photochemistry of oligosilanes

2003 ◽  
Vol 75 (8) ◽  
pp. 999-1020 ◽  
Author(s):  
H. A. Fogarty ◽  
D. L. Casher ◽  
Roman Imhof ◽  
T. Schepers ◽  
D. W. Rooklin ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Chain Length ◽  
Spectral Properties ◽  
Electronic States ◽  
Photochemical Reactions ◽  
Low Energy ◽  
Electron Systems ◽  
Current State ◽  
The Individual ◽  
Almost All

The making and breaking of σ bonds is an integral part of almost all photochemical reactions. Yet, the electronic states of σ electrons are not nearly as well understood as the states of π-electron systems. Efforts in our laboratory to enhance the current state of their understanding are described, using the specific example of oligosilanes. We address the intrinsically cyclic nature of σ delocalization and its dependence on chain length and conformation, both in terms of theory and spectroscopic experiments, from the simplest disilane chromophore to the spectral properties of the individual conformers of permethylated heptasilane. We also describe a new low-energy luminescence from certain conformers of permethylated oligosilanes.

scholarly journals Composition-Induced Magnetic Transition in GdMn1-xTixSi Intermetallic Compounds for x = 0–1

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1296
Author(s):  
Roman D. Mukhachev ◽  
Alexey V. Lukoyanov
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
Intermetallic Compounds ◽  
Magnetic Transition ◽  
Magnetic Moments ◽  
Electronic States ◽  
Magnetic Characteristics ◽  
Significant Change ◽  
Ternary Intermetallic Compounds ◽  
Almost All

Magnetic intermetallic compounds based on rare earth elements and 3d transition metals are widely investigated due to the functionality of their physical properties and their variety of possible applications. In this work, we investigated the features of the electronic structure and magnetic properties of ternary intermetallic compounds based on gadolinium GdMn1-xTixSi, in the framework of the DFT + U method. Analysis of the densities of electronic states and magnetic moments of ions in Ti-doped GdMnSi showed a significant change in the magnetic properties depending on the contents of Mn and Ti. Together with the magnetic moment, an increase in the density of electronic states at the Fermi energy was found in almost all GdMn1-xTixSi compositions, which may indicate a significant change in the transport properties of intermetallic compounds. Together with the expected Curie temperatures above 300 K, the revealed changes in the magnetic characteristics and electronic structure make the GdMn1-xTixSi intermetallic system promising for use in microelectronic applications.

scholarly journals Probing the Electronic Structure of Bulk Water at the Molecular Lengthscale with Angle-Resolved Photoelectron Spectroscopy

2020 ◽  
Author(s):  
Samer Gozem ◽  
Robert Seidel ◽  
Uwe Hergenhahn ◽  
Evgeny Lugovoy ◽  
Bernd Abel ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Photoelectron Spectroscopy ◽  
Anisotropy Parameter ◽  
High Energy ◽  
Bulk Water ◽  
Low Energy ◽  
Water Molecules ◽  
Neat Water ◽  
Energy Regime ◽  
The Individual

<div>We report a combined experimental and theoretical study of bulk water photoionization. Angular distributions of photoelectrons produced by ionizing the valence band of neat water using X-ray radiation (250-750 eV) show a limited (<30 %) decrease in the beta anisotropy parameter compared to the gas phase, indicating that the electronic structure of the individual water molecules can be probed. By theoretical modeling using high-level electronic structure methods, we show that in a high-energy regime photoionization of bulk can be described as an incoherent superposition of individual molecules, in contrast to a low-energy regime where photoionization probes delocalized entangled states of molecular aggregates. The two regimes-low energy versus high energy-are defined as limiting cases where the de Broglie wavelength of the photoelectron is either larger or smaller than the intermolecular distance between water molecules, respectively. The comparison of the measured and computed anisotropies reveals that at high kinetic energies the observed reduction in beta is mostly due to scattering rather than rehybridization due to solvation.</div>

scholarly journals Probing the Electronic Structure of Bulk Water at the Molecular Lengthscale with Angle-Resolved Photoelectron Spectroscopy

2020 ◽  
Author(s):  
Samer Gozem ◽  
Robert Seidel ◽  
Uwe Hergenhahn ◽  
Evgeny Lugovoy ◽  
Bernd Winter ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Photoelectron Spectroscopy ◽  
Anisotropy Parameter ◽  
High Energy ◽  
Bulk Water ◽  
Low Energy ◽  
Water Molecules ◽  
Neat Water ◽  
Energy Regime ◽  
The Individual

<div>We report a combined experimental and theoretical study of bulk water photoionization. Angular distributions of photoelectrons produced by ionizing the valence band of neat water using X-ray radiation (250-750 eV) show a limited (<30 %) decrease in the beta anisotropy parameter compared to the gas phase, indicating that the electronic structure of the individual water molecules can be probed. By theoretical modeling using high-level electronic structure methods, we show that in a high-energy regime photoionization of bulk can be described as an incoherent superposition of individual molecules, in contrast to a low-energy regime where photoionization probes delocalized entangled states of molecular aggregates. The two regimes-low energy versus high energy-are defined as limiting cases where the de Broglie wavelength of the photoelectron is either larger or smaller than the intermolecular distance between water molecules, respectively.</div>

scholarly journals Probing the Electronic Structure of Bulk Water at the Molecular Lengthscale with Angle-Resolved Photoelectron Spectroscopy

2020 ◽  
Author(s):  
Samer Gozem ◽  
Robert Seidel ◽  
Uwe Hergenhahn ◽  
Evgeny Lugovoy ◽  
Bernd Abel ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Photoelectron Spectroscopy ◽  
Anisotropy Parameter ◽  
High Energy ◽  
Bulk Water ◽  
Low Energy ◽  
Water Molecules ◽  
Neat Water ◽  
Energy Regime ◽  
The Individual

<div>We report a combined experimental and theoretical study of bulk water photoionization. Angular distributions of photoelectrons produced by ionizing the valence band of neat water using X-ray radiation (250-750 eV) show a limited (<30 %) decrease in the beta anisotropy parameter compared to the gas phase, indicating that the electronic structure of the individual water molecules can be probed. By theoretical modeling using high-level electronic structure methods, we show that in a high-energy regime photoionization of bulk can be described as an incoherent superposition of individual molecules, in contrast to a low-energy regime where photoionization probes delocalized entangled states of molecular aggregates. The two regimes-low energy versus high energy-are defined as limiting cases where the de Broglie wavelength of the photoelectron is either larger or smaller than the intermolecular distance between water molecules, respectively. The comparison of the measured and computed anisotropies reveals that at high kinetic energies the observed reduction in beta is mostly due to scattering rather than rehybridization due to solvation.</div>

Localized electronic states in amorphous semiconductors

1977 ◽  
Vol 55 (11) ◽  
pp. 1920-1929 ◽  
Author(s):  
David Adler ◽  
Ellen J. Yoffa
Keyword(s):  
Electronic Structure ◽  
Simple Model ◽  
Hubbard Model ◽  
Minimum Energy ◽  
Electronic States ◽  
Amorphous Semiconductors ◽  
Localized States ◽  
Local Coordination ◽  
Defect Sites ◽  
Almost All

The experimental results pertaining to the electronic structure of covalent amorphous semiconductors are briefly reviewed. It is found that three classes of materials exist, depending on the lowest-energy coordination of the predominant chemical component. In each case, the transport properties are ordinarily controlled by the localized states in the gap resulting from the minimum-energy defect sites, in which the local coordination is not optimal for certain atoms. These localized states are treated in terms of a Hubbard model, in which the effective repulsion between two electrons simultaneously present on the same center is taken as positive for tetrahedrally bonded solids and negative for chalcogenide and pnictide glasses. The electronic structure is discussed in detail. It is shown that even such a simple model can account for almost all of the experimental properties of the major classes of amorphous semiconductors.

ELECTRONIC STRUCTURE FOR THE TWO-BAND HUBBARD MODEL OF THE LADDER α′-NaV2O5 COMPOUND

2005 ◽  
Vol 19 (30) ◽  
pp. 4399-4417
Author(s):  
Ž. Lj. KOVAČEVIĆ ◽  
F. R. VUKAJLOVIĆ
Keyword(s):  
Electronic Structure ◽  
Hubbard Model ◽  
Green’S Function ◽  
Electronic Spectrum ◽  
Green's Function ◽  
Electronic States ◽  
Low Energy ◽  
Projection Technique ◽  
Singlet States ◽  
Hubbard Operators

An effective Hubbard model for one-particle d-like states and two-particle singlet states is derived in order to describe the low-energy electronic spectrum in ladder α′- NaV 2 O 5 compound. The energy shifts and the renormalized hopping parameters for the considered electronic states are calculated on the basis of the projection technique for the two-time matrix Green's function in terms of Hubbard operators.

Direct Observation of Chain Lengths and Conformations in Oligofluorene Distributions from Controlled Polymerization by Double Electron-Electron Resonance

2019 ◽  
Author(s):  
Dennis Bücker ◽  
Annika Sickinger ◽  
Julian D. Ruiz Perez ◽  
Manuel Oestringer ◽  
Stefan Mecking ◽  
...  
Keyword(s):  
Chain Length ◽  
Length Distribution ◽  
Catalyst System ◽  
Chain Conformation ◽  
Controlled Polymerization ◽  
Chain Length Distribution ◽  
Electron Resonance ◽  
Double Electron ◽  
The Individual ◽  
Double Electron Electron Resonance

Synthetic polymers are mixtures of different length chains, and their chain length and chain conformation is often experimentally characterized by ensemble averages. We demonstrate that Double-Electron-Electron-Resonance (DEER) spectroscopy can reveal the chain length distribution, and chain conformation and flexibility of the individual n-mers in oligo-(9,9-dioctylfluorene) from controlled Suzuki-Miyaura Coupling Polymerization (cSMCP). The required spin-labeled chain ends were introduced efficiently via a TEMPO-substituted initiator and chain terminating agent, respectively, with an in situ catalyst system. Individual precise chain length oligomers as reference materials were obtained by a stepwise approach. Chain length distribution, chain conformation and flexibility can also be accessed within poly(fluorene) nanoparticles.

scholarly journals Structural and spectral properties of a non-classical C58 isomer and its fluorinated derivatives in theory

RSC Advances ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 1472-1481
Author(s):  
Xiaoxi Song ◽  
Renfeng Mao ◽  
Ziwei Wang ◽  
Jiayuan Qi
Keyword(s):  
Electronic Structure ◽  
Spectral Properties ◽  
X Ray ◽  
System P ◽  
Fluorinated Derivatives

The X-ray spectra have good isomer dependence and give a comprehensive insight of the electronic structure of the system.

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