Ionization Energies and Dyson Orbitals of the Iso-electronic SO₂, O₃, and S₃ Molecules from Electron Propagator...

Adiabatic and vertical ionization energies corresponding to the X̃ $$, à $$, and B̃ $$ final states of SO₂⁺, O₃⁺, and S₃⁺ have been calculated with a variety of electron-propagator and coupled-cluster methods. The BD-T1 electron-propagator method for vertical ionization energies and coupled-cluster adiabatic and zero-point corrections yield agreement with experiment to within 0.1 eV in all cases but one. The remaining discrepancies for the à $$ state of SO₂⁺ indicate a need for higher levels of theory in determining cationic minima and their accompanying vibrational frequencies. Predictions for the still unobserved à $$ and B̃ $$ final states of S₃⁺ are included. To account for increased biradical character in O₃ and S₃, highly correlated reference states are required to produce the correct order of final states. Electron correlation plays a subtle role in determining the contours of the Dyson orbitals obtained with BD-T1 and NR2 electron-propagator calculations.