Piezoreflectance spectra of potassium iodide were measured from 5 to 30 eV in the fundamental and core excitation region. The deformation potentials cubic, tetragonal and trigonal, were deduced for twenty six structures observed in this energy region and are analyzed in terms of a simple point ion model to identify the electronic origins of these structures.
An analytic treatment is given for the deviations of XAS and XPS intensities from the asymptotic power-law behaviors given by Nozières and de Dominicis (ND). In deriving the formulae, the core-hole potential is assumed to be of contact-type and the energy dependences of physical quantities such as the phase shift and the dispersion integrals are taken into account up to linear terms with respect to the energy. It is shown that the deviations from the asymptotic formulae are expressed by introducing several new quantities which are derived from the first principle. It is also found that the deviations can be incorporated in the framework of the generalized (frequency-dependent) power-law. By comparing with the exact numerical results, the obtained formulae are demonstrated to have much wider applicability in the frequency space than the asymptotic ND formulae.
A new model is presented for interionic potentials between alkali and halogen ions in which charge-transfer (CT) excitation from an anion to a cation is taken into account. The experimental molecular constants of twenty alkali halide molecules have been used to determine the contribution of the overlap repulsion and the CT interaction. The resulting potentials can reproduce cohesive properties of the corresponding solids well, such as crystal structure, lattice constant, and cohesive energy. The results are discussed compared with the traditional Born-Mayer theory and the shell model.