Molecular orbitals ionization cross section

At energies higher than 10 keV, ionization cross sections were calculated using Seltzer s formula [183]. Seltzer s formula gives the partial ionization cross sections for five molecular orbitals of water. The total ionization cross sections in the energy range of 10 keV to 10 MeV were obtained by summing up all the partial cross sections (Fig. 8). 

However, there has still been problem in their calculation. In the molecular orbital calculation, the basis set is often expanded so as to include some excited atomic orbitals in order to achieve a high accuracy. For estimation of the peak intensity of the XPS spectrum, information of the ionization cross section for the atomic orbital employed for the basis function is required. By the use of Hatree-Fock-Slater model, the ionization cross sections for atomic sub-shell orbitals have been calculated by several authors . Although these data are very useful for evaluation of the XPS... 

Change in the Ionization Cross Section and Splitting of theK L Line due to Molecular Orbital Formation... 

The ionization cross section can be written in the atomic frame and estimated using SCA, as explained in the previous chapter, for all the X-ray transitions in isolated atoms, and for the X-ray transitions which occur between two inner shells for atoms in atom-aggregates. However, for atom-aggregates, if valence shells are involved in the X-ray transitions then we have to take molecular orbital effects on the ionization cross... 

Brief descriptions are given in the following of needed aspects of cross sections, molecular orbitals, and of the more recently devised Stieltjes orbitals that have proved useful in spectral studies. Examples of the use of the Stieltjes formalism In identifying Mulliken valence orbitals in the cross sections of diatomic and polyatomic compounds are reported next. Also indicated are more general aspects of such intravalence transitions as they relate to electron-impact resonances in selected cases. The Importance of dealing with both discrete and continuous spectral intervals on a common basis is emphasized throughout, particularly with reference to the clarification of the positionings of a-xj and tv-ht excitations in molecular photoabsorption and ionization cross sections. 

The modified additivity rule introduced by Deutsch et al. (1997) attempted to account for the effects of molecular bonding by introducing empirically determined weighting factors that depend on the atomic orbital radii and the electron occupation numbers of the various atomic orbitals. A detailed comparison with existing molecular ionization cross section data for molecules of the form AB suggested the following explicit form of the ionization cross section of... 

It is quite different from spectra for solids. The cause of enhanced KL , KL, and KL peaks for the solid as compared to the gas is not fully understood. Similar chemical effects on satellite lines were observed by Uda et al. and attributed to two causes change in ionization cross sections and reconstruction of molecular orbitals... 

For PE spectra of metal compounds where vibrational fine structures are not resolved, the identification of the nature of the ionized MOs is often aided by taking the advantage of the photon energy dependence of molecular ionization cross sections. It has been shown early that the intensities of the metal d orbital ionization bands increase dramatically from He to He (40.8 eV) radiation, compared to those of ligand-based s and p ionization bands. " This is known as the He /He intensity rule. More recently, synchrotron radiation has been employed to measure relative band intensities at different photon wavelengthsThe synchrotron radiation has... 

The study of the photoionization cross section as a function of photon energy for the different orbitals of Me4Sn, which can be a powerful tool for the assignment of the spectra and the analysis of the contribution of the various atomic orbitals to the molecular orbitals, has been carried out by the authors of References 11 and 12 by using He I and He II as ionizing source, and of Reference 13 by using synchrotron radiation. Bertoncello... 

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