Abstract Geometry optimization and harmonic vibrational frequency calculations have been performed on the X ˜ 2 A 1 state of PO 2 radicals and X ˜ 1 A 1 state of PO 2 - anions. Franck–Condon analysis and spectral simulations were carried out on the PO 2 ( X 2 A 1 ) – PO 2 - ( X 1 A 1 ) photodetachment process. The theoretical spectra obtained by using CCSD/6-311+G(2p, d) values are in agreement with the observed one. In addition, the equilibrium geometry parameters, r(PO) = 1.504 ± 0.005 Å and ∠(OPO) = 119.0 ± 0.2°, of the X ˜ 1 A 1 state of PO 2 - are derived by employing an iterative Franck–Condon analysis procedure in the spectral simulation. Furthermore, through the different methods, our best calculated electron affinity is 78.80 cal mol −1, which is in excellent agreement with the experimental value and other theoretical values.