Inner-shell electron excitation spectroscopy

Inner-shell Electron Excitation Spectroscopy (ISEES)... 

Table 14 Study of Inner-shell Electron Excitation Spectroscopy of Is -> rr Transitions (in eV)...

The performance of DFT in the optimization of molecular geometry is summarized in Section 4. In Section 5, we present DFT results for the vibrational spectra of molecules. It is well known that HF harmonic vibrational frequencies are about 10% higher than the experimental harmonic frequencies. Vibrational frequencies computed at correlated levels of methods improve the agreement, but they are usually computationally too costly to be feasible for medium-sized molecules. Since DFT is computationally more economical than the HF method, the accuracy of DFT predicted vibrational frequencies is of great interest to us. Section 6 summarizes the DFT results for electron spectroscopy including core-electron binding energies (CEBEs) which are measured by the so-called electron spectroscopy for chemical analysis (ESCA), and inner-shell electron excitation spectra (ISEES). 

Excitation of inner-shell electrons X-ray photoelectron spectroscopy, XPS... 

This technique is also known as electron spectroscopy for chemical analysis (ESCA). Although it is concerned with the detection of electrons, it is discussed here because the way in which the photoelectrons are produced is fundamental to the XRF process. As described above, an incident X-ray photon produces an excited ion by ejecting an inner shell electron. The excited... 

In addition to using X-rays to irradiate a surface, ultraviolet light may be used as the source for photoelectron spectroscopy (PES). This technique, known as ultraviolet photoelectron spectroscopy (UPS, Figure 7.38), is usually carried out using two He lines (Hel at 21.2 eV and Hell at 40.8 eV), or a synchrotron source. This technique is often referred to as soft PES, since the low photon energy is not sufficient to excite the inner-shell electrons, but rather results in photoelectron emission from valence band electrons - useful to characterize surface species based on their bonding motifs. It should be noted that both UPS and XPS are often performed in tandem with an Ar" " source, allowing for chemical analysis of the sample at depths of < 1 J,m below the surface. 

X-ray photoelectron spectroscopy Mossbauer spectroscopy X-ray singlecrystal diffraction XPS (ESCA) Inner-shell electron transitions. Excitation of nuclear spin by y rays. Fourier transform of diffraction data reveals location of electron density. Oxidation state of metal. Oxidation and spin state. Antiferromagnetic coupling (Fe only). Precise three-dimensional structure, bond distances and angles for small molecules. Lower resolution and precision for proteins. 

Ishii I, Hitchcock AP (1988) The Oscillator strengths for C Is and Ols excitation of some saturated and unsaturated organic alcohols, acids and esters. J Electron Spec Phen 46 55-84 Ishii I, McLaren R, Hitchcock AP, Jordan KD, Choi Y, Robin MB (1988) The a molecular orbitals of perfluoroalkanes as studied by inner-shell electron energy-loss and electron transmission spectroscopies. Can J Chem 66 2104-2121... 

Sze KH, Brion CE (1991) Inner-shell and valence-shell electronic excitation of cyclopropane and ethylene oxide by high resolution electron energy loss spectroscopy. J Electron Spectrosc Relat Phenom 57 117-135... 

There are a number of mechanisms by which inelastic electron scattering can occur, all of which will contribute to the intensity observed in the EELS spectrum. However, for the present purposes, we will mainly focus on the case where the impinging high energy electrons in the TEM ionize atoms within the specimen via the ejec-uon of an inner-shell electron from the nucleus. The energy transfer required for these ionization processes are highly specific to the identity of the excited atom and, as such, form the basis for elemental and chemical analysis via EELS spectroscopy. 

Using the linear polarization of synchrotron radiation is fundamental to describe unoccupied states in molecular inner-shell spectroscopy. Because the core level electron is localized on a definite atom, spectroscopy based on core excitation into unoccupied valence MOs appear simplified with respect to valence electrons excitation spectroscopy. 

States with an excitation energy higher than about 6 eV are difficult to study in optical spectroscopy. This is particularly important for highly excited ion states that correspond to the removal of an inner shell electron. 

Shorter-wavelength radiation promotes transitions between electronic orbitals in atoms and molecules. Valence electrons are excited in the near-uv or visible. At higher energies, in the vacuum uv (vuv), inner-shell transitions begin to occur. Both regions are important to laboratory spectroscopy, but strong absorption by make the vuv unsuitable for atmospheric monitoring. Electronic transitions in molecules are accompanied by stmcture... 

Firstly, the energy losses of the incident electrons which produce the inner shell excitations may be detected as peaks in electron energy loss spectroscopy (EELS). The elecrons transmitted by the specimen are dispersed in a magnetic field spectrometer and the peaks, due to K, L and other shell excitations giving energy losses in the range of 0-2000eV, may be detected and measured. 

---