Ab initio calculations have been performed to study the molecular structures and the vibrational levels of the low-lying ionic states ((2)Pi(g), (2)Pi(u), (2)Sigma(u)(+), and (2)Sigma(g)(+)) of CO2 and CS2. The global regions of the potential energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. The vibrational calculations using the explicit vibrational Hamiltonians have been used for the vibrational analysis. The equilibrium molecular structures and the vibrational analysis of the ionic states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectra.