A difficult assignment problem the ionic states of ozone and sulphur dioxide

From the experimental photoelectron spectra no definite assignment of the ionization potentials of O₃ and SO₂ could be deduced. The interpretation of the vibrational structure in the spectrum of O₃ has also been controversial. The present work reports on a many-body calculation of the ionization potentials and the vibrational structure due to ionization of O₃ and SO₂. For the three lowest ionization potentials of both molecules the ordering au a₂, b₂ is obtained. For O₃, this assignment is in agreement with results obtained by Basch, but disagrees with the results of all other calculations (ASCF, Cl, GVB-CI, LCAO-X_α,SW-X_α, INDO, etc.) reported in the literature. For SO₂ no ab initio calculations have been reported which go beyond the Hartree- Fock level. We find that the stretching mode is excited in the a2 band and the bending mode in the b₂ band of O₃. The excitation of the bending mode dominates in all three bands of SO₂.