The structure of the spectrum of the partial density of filled states of Bi₂Sr₂CaCu₂O₈ in the range E_b<4 eV, obtained by ultraviolet (hv= 8.43 eV) photoelectron spectroscopy was compared with that calculated by the strong coupling method. The results of the calculations agree with the experimental results in the range of binding energies 1<Eb<4 eV. Analysis of the evolution of the spectra under thermal and phototreatment in ultrahigh vacuum and in oxygen reveals that oxygen atoms from Cu-O planes possess the highest mobility in the lattice and the surface of the single crystal is formed by Bi-O planes.