  We present metal 3s x-ray photoelectron spectra of different transition metal
oxides. The values of the 3s exchange splitting for the 3d metal oxides are
given as a function of the 3d electron number in the ground state. The spectra
were analysed using the simple two-configuration model of the interatomic
configuration mixing. The change of the 3s spectra is ascribed to the change of
the charge-transfer energy.
