Ab initio study of the electronic spectrum of the PO2 radical

Ab initio electronic structure calculations are reported for 18 electronic states of the PO2 radical. Geometric parameters for the X 2A1 ground state are calculated at the MRD-CI level with a triple-zeta basis set plus two polarization d functions, as well as Rydberg functions. The vertical excitation energies, oscillator strengths and radiative lifetimes for these states are determined at the ground state equilibrium conformation. The equilibrium geometries and adiabatic excitation energies for the three lowest-lying electronic excited states 1 2B2, 1 2A2 and 1 2B1 (2Πu), force constants and vibrational frequencies for the X 2A1 ground state and these three excited states are also calculated, and are found to be in good agreement with experimental data.