As we know, valence electrons penetrate the ion core slightly. When they happen to be inside the core, their charge repels the charge of the core electrons. In other words, the effect of the valence charge in the core region is to screen partially the core electron–nucleus attraction. This reduces the binding energies of the core levels. When the valence charge is removed or transferred from the atom, the screening is reduced. As a result, the screening is reduced; the cation-core electrons are attracted more strongly to the nucleus. Thus all inner (core) levels of an atom are shifted by fractions of 1 eV to a few eV when the valence electron configuration changes on bonding.The binding energy increases (decreases) if electrons are lost (gained). In our case, when the Ti4+ transfer to Ti3+, one electron is gained. As a result, the binding energy of Ti 2p3/2 decreases about 1 eV