A difficult assignment problem

Abstract

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 a ₁, a ₂, b ₂ is obtained. For O₃, this assignment is in agreement with results obtained by Basch, but disagrees with the results of all other calculations (ΔSCF, CI, 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 a ₂ band and the bending mode in the b ₂ band of O₃. The excitation of the bending mode dominates in all three bands of SO₂.