The low lying electronic states of O−3

The energies of the three lowest lying excited states of the ozonide anion (1 2B2, 1 2A1, 1 2A2) at the optimized geometry of the X 2B1 ground state are theoretically predicted at the MRCI-SD level of theory using large atomic natural basis sets. The calculated vertical excitation energy Tv=2.85 eV for the 1 2A2←X 2B1 transition, which has a large transition moment, is in good agreement with the experimental results for the isolated O3− anion in host matrices and solution between 2.69–2.81 eV. The state symmetry forbidden transition 1 2B2←X 2B1 is calculated with Tv=2.26 eV. The excitation energy for the 1 2A1←X 2B1 transition is theoretically predicted with Tv=2.28 eV and a very low transition moment. The theoretical results are also discussed in comparison with recently observed low lying absorption bands of O3−.