Results from electron spectroscopy

Coulomb correlation energy, I/44, and thereby showed how the cationic and anionic energy levels were both equally important. These workers calculated the gap arising in the charge excitation spectrum of a single transition-metal impurity hybridizing with a 

The ZSA phase diagram and its variants provide a satisfactory description of the overall electronic structure of stoichiometric and ordered transition-metal compounds. Within the above description, the electronic properties of transition-metal oxides are primarily determined by the values of A, and t. There have been several electron spectroscopic (photoemission) investigations in order to estimate the interaction strengths. Valence-band as well as core-level spectra have been analysed for a large number of transition-metal and rare-earth compounds. Calculations of the spectra have been performed at different levels of complexity, but generally within an Anderson impurity Hamiltonian. In the case of metallic systems, the situation is complicated by the presence of a continuum of low-energy electron-hole excitations across the Fermi level. These play an important role in the case of the rare earths and their intermetallics. This effect is particularly important for the valence-band spectra. 

Analysis of the valence-band spectrum of NiO helped to understand the electronic structure of transition-metal compounds. It is to be noted that th.e crystal-field theory cannot explain the features over the entire valence-band region of NiO. It therefore becomes necessary to explicitly take into account the ligand(02p)-metal (Ni3d) hybridization and the intra-atomic Coulomb interaction, 11, in order to satisfactorily explain the spectral features. This has been done by approximating bulk NiO by a cluster (NiOg) . The ground-state wave function Tg of this cluster is given by, 

The calculation of the core levels of LajCuO discussed above was performed within the cluster approximation wherein the dependence of the spectral shape on the oxygen band-width is missed out. In order to include the effect of the oxygen 2p derived band on the spectral shape, the core-level photoemission calculation has to be performed within the impurity model which includes the O 2p band-width (instead of a single O 2p level). For reasonable values of the hybridization strength, t, the range of values of A is such that the Cu appears close to the bottom of the 

We discussed above the analysis of core-level spectra from cuprates which contain only a single hole in the d-band per Cu ion. This makes an irrelevant parameter within an impurity model. However, analysis can also be carried out for systems where [7dd plays a significant role. This is illustrated by the analysis of the core-level spectrum of LaCoOj carried out within the impurity model (Chainani et al, 1992). This oxide is modelled by the (CoOg) cluster with the transition-metal ion being formally in the 3 + oxidation state and in an octahedral crystal field. One has to therefore take into account interactions between various configurations such as d , d Z, .  

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Zubenko GS, Kopp U, Seto T, Firestone LL (1999) Platelet membrane fluidity individuals at risk for Alzheimer s disease a comparison of results from fluorescence spectroscopy and electron spin resonance spectroscopy. Psychopharmacology (Berl) 145(2) 175-180... 

Results for CO/Cu(001) were obtained with a model of electronic and vibrational transitions we have previously derived, with populations and quantum coherences calculated to compare with experimental results from femtosecond spectroscopy and time-of flight measurements. The present results show that the populations of individual vibronic states oscillate as a result... 

Opacity of mixed-valence minerals. The opacities of many end-member Fe2+-Fe3+ oxide and silicate minerals result from electron hopping between neighbouring cations when they are located in infinite chains or bands of edge-shared octahedra in the crystal structures. Opaque minerals such as magnetite, ilvaite, deerite, cronstedtite, riebeckite and laihunite owe their relatively high electrical conductivities to thermally activated electron delocalization, contributing to intermediate valence states of iron cations which may be detected by Mossbauer spectroscopy. 

FIGURE 2. (a) Schematic energy scale for electronic ground (r) and exited (yj) states of a neutral molecule M, its radical cation M e generated by ionization or oxidation and its radical anion M e and dianion M" resulting from electron insertion. Representative measurement methods used in many investigations are NMR, IR, UV, PE, ESR and ENDOR spectroscopy as well as cyclic voltammetry (CV). (b) Qualitative molecular-state model, (c) Schematic time scale for molecular states and their changes (in seconds, the time unit intermediate between the duration of a human heart-beat and the transmission of stimuli by the eye)10 0 Radiation frequencies and 0 measurement methods and information obtained... 

To bridge the gap between ideal and practical catalysts, optical spectroscopies, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and Mossbauer spectroscopy can be used. All have been reviewed recently (373, 396), and some examples have been cited earlier (107, 108). Electron spin resonance has been used in several studies of electroorganic reactions (357,371). It can detect short-lived radicals resulting from electron transfer. Recent application of Mossbauer spectroscopy in situ in electrochemical cells deserves mentioning, although it addressed only the anodic polarization and film stability of Co- and Sn-coated electrodes (397,398). Extension to electrocatalytic studies involving Mossbauer nuclides seems feasible. 

The use of electronic spectroscopy to follow polymer reactions has been limited because of the broad spectra resulting from electronic transitions and the lack of molecular structural information in the spectra. The only exception to this is in polymer photochemistry, where information regarding the excited states and the pathways for energy loss may be exploited... 

Fig. 2. Molecular states and relevant measurement data Total energy scale for electronic ground (F) and excited (XI) states of a neutral molecule M and its radical cations M" or dications generated by ionization or oxidation or its radical anions M " and dianions resulting from electron insertion. In addition, the measurement methods used by the Frankfurt Group are indicated, especially UV, PES, ESR, and ENDOR spectroscopy as well as polarography (POL) or cyclic voltammetry (CV).

The result from Mossbauer spectroscopy is that tin in a-SnF2 has a stereoactive lone pair of electrons. Is the presence of a stereoactive lone pair compatible with the tin Wyckoff sites determined by Bergerhoff [99] That is the question. While there is no symmetry constrains on the general 8f site that can, therefore, accommodate any site distortion, including the presence of a lone pair, compatibility between the presence of a stereoactive lone pair and the local symmetry of the two special sites (4b and 4e) proposed by Bergerhoff must be investigated. A lone pair is axial and can, therefore, be accommodated on a site with axial symmetry, such as a rotation axis, provided some conditions are met. In BergerhofPs... 

NF2 Radical g Factor and Hyperfine Coupling Constants. Results from Electron Spin Resonance and Microwave Spectroscopy. 

X-ray absorption spectroscopy (XAS), including X-ray absorption near edge structure (XANES) and X-ray absorption fine structure (XAFS), is based on resonant absorption processes resulting from electronic transitions from core levels to vacant orbitals and to the continuum, respectively (Figure 12.1). XANES measures dipole-mediated transitions from a deep core orbital to unoccupied orbitals and proceeds from an initial state i) to a final state [/). The transitions from Is, 2s, p, 3s, p, d, and so on, to higher states or continuum correspond to K-, L-, M-,... edge absorptions. The absorption p E) is... 

An overview of the thermodynamics of vapor complexation will be given in sect. 4.1. The electronic absorption spectra and the systematics of the possible structures of vapor complexes will be discussed in sect. 4.2. Finally, an account of results from fluorescence spectroscopy will be presented in sect. 4.3. 

X-ray photons result from electronic transitions between the inner energy levels of atoms. When high-energy electrons are absorbed by matter, an x-ray line spectrum results. The structure depends on the substance and is thus used in x-ray spectroscopy. The line spectrum is always formed in conjunction with a continuous background spectrum. The minimum (cutoff) wavelength Xq corresponds to the maximum x-ray energy, This equals the... 

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