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Volume 92, Number 4. Previous Article Next Article. Research Article April 01, Stoyanov E. Google Scholar. Langenhorst F. Steinle-Neumann G. American Mineralogist 92 4 : Article history received:. Abstract Titanium L 3,2 and O K electron energy loss near-edge structures ELNES of seven Ti oxides have been measured in a transmission electron microscope to obtain information on the valence state and site geometry of Ti.
You do not currently have access to this article. You could not be signed in. Librarian Administrator Sign In. Buy This Article. Email alerts New issue alert. Finally, the occurrence of singlet or triplet ground states in the series of molecules studied is rationalized upon the interplay of the parameters extracted. This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. The article explains the preferred shape of chlorine trifluoride ClF3 ,….
Valence-state reflectometry of complex oxide heterointerfaces
The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites.
Valence ionized states of iron pentacarbonyl and eta5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy. Valence ionized states of iron pentacarbonyl Fe CO 5 and eta 5 -cyclopentadienyl cobalt dicarbonyl Co eta 5 -C 5 H 5 CO 2 have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy 2D-PIES , and symmetry-adapted cluster-configuration interaction calculations.
Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra.
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The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe CO 5 , an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. Inelastic collisions of positrons with one- valence-electron targets. The total elastic and positronium formation cross sections of the inelastic collisions between positrons and various one- valence-electron atoms, namely hydrogen, lithium, sodium, potassium and rubidium , and one- valence-electron ions, namely hydrogen-like, lithium-like and alkaline-earth positive ions are determined using an elaborate modified coupled-static approximation.
Special attention is devoted to the behavior of the Ps cross sections at the energy regions lying above the Ps formation thresholds. Optical activity and electronic absorption spectra of some simple nucleosides related to cytidine and uridine: all- valence -shell molecular orbital calculations. PubMed Central. The circular dichroism and electronic absorption of three simple model systems for cytidine and uridine have been measured to nm.
The molecular spectral properties excitation wavelengths, oscillator strengths, rotational strengths, and polarization directions and electronic transitional patterns were investigated by using wave functions of the entire nucleoside with the goal of establishing the reliability of the theoretical method.
The computed electronic absorption quantities were shown to be in satisfactory agreement with experimental data. It was found that the computed optical rotatory strengths of the B2u and E1u electronic transitions and lowest observed n-pi transition are in good agreement with experimental values. Electronic transitions were characterized by their electronic transitional patterns derived from population analysis of the transition density matrix.
The theoretical rotational strengths associated with the B2u and E1u transitions stabilize after the use of just a few singly excited configurations in the configuration interaction basis and, hypothetically, are more reliable as indicators of conformation in pyrimidine nucleosides related to cytidine. Real-time observation of valence electron motion.
The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump-probe measurement of the density matrix of valence electrons in atomic krypton ions.
Electron Transfer: Ionic Bonds
We generate the ions with a controlled few-cycle laser field and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble.
Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes.
Coupled-cluster based basis sets for valence correlation calculations. Novel basis sets are generated that target the description of valence correlation in atoms H through Ar. The new contraction coefficients are obtained according to the Atomic Natural Orbital ANO procedure from CCSD T coupled-cluster singles and doubles with perturbative triples correction density matrices starting from the primitive functions of Dunning et al.
The exponents of the primitive Gaussian functions are subject to uniform scaling in order to ensure satisfaction of the virial theorem for the corresponding atoms. Cluster molecular orbital description of the electronic structures of mixed- valence iron oxides and silicates.
Why Does the Boiling Point Increase When the Atomic Radius Increases in Halogens? | Sciencing
A molecular orbital description, based on spin-unrestricted X?? The cluster calculations show that electron hopping and optical intervalence charge-transger result from weak FeFe bonding across shared edges of FeO6 coordination polyhedra. Study of average valence and valence electron distribution of several oxides using X-ray photoelectron spectra. The absolute values of ValO for these samples were found to be distinctly lower than the traditional value of 2.
In addition, we analyzed the valence band spectra of the samples and investigated the distribution characteristics of the valence electrons. Auger electron emission initiated by the creation of valence -band holes in graphene by positron annihilation. Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids.
However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band.
These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons valence -band holes by annihilation.
Chirayath, V. Electric-field-driven electron -transfer in mixed- valence molecules. Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed- valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling.
The operation of such a device relies on nonequilibrium electron transfer ET , whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate the electric-field-driven ET rate for a model mixed- valence compound. The mixed- valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment.
Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed- valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.
Blair, Enrique P. Valence and ionic lowest-lying electronic states of ethyl formate as studied by high-resolution vacuum ultraviolet photoabsorption, He I photoelectron spectroscopy, and ab initio calculations.
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Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He I photoelectron spectrum from Electronics Environmental Benefits Calculator.
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