A theoretical study on the inner-valence photoelectron spectra lying between 21 and 26 eV of the O2 molecule

Ab initio calculations were carried out to study the structures of the photoelectron spectra of the O(2) molecule using complete active space self-consistent field and multireference single and double excitation configuration interaction methods. We focused our attention primarily on the inner-valence ionized states lying below 26 eV. Vibrational levels were calculated using adiabatic potential curves and vibrational wave functions were used to obtain Franck-Condon factors. We show that not only discrete vibrational levels of (3) (2)Pi(u), but also the continuum of nuclear motion in (1) (2)Sigma(u) (-) contribute to the bands of vibrational progression and the broad peak of the continuum between 22.5 and 26 eV. Other states with weak intensity lying between 19 and 26 eV are also discussed.