Radiative transitions in TiO: Ab initio oscillator strengths and lifetimes for low-lying electronic states

The dipole transition moments, oscillator strengths and radiative lifetimes for seven low-lying triplet and ten singlet electronic states of the TiO molecule have been calculated using the multireference singles and doubles configuration interaction method (MRCI) and compared with the available literature data. Our MRCI results support the previous theoretical transition moments reported by Langhoff ([CITE]) for the most of the computed bands except for the δ and ϕ ones. For the δ band our computed electronic oscillator strength fe is 0.0581 which is considerably smaller than that of Langhoff (0.096). Our fe supports the proposal of Plez ([CITE]) that the value of Langhoff should be divided by ∼2 to match observations. Our MRCI calculations give fe of 0.0668 for the ϕ band. This is larger than the value of 0.036 obtained by Langhoff. We adduce strong arguments that our fe for the ϕ band is reasonable. We predict two new $^1\Pi$ and one $^1\Phi$ states which exhibit avoided crossings with the known $b^1\Pi$ and $c^1\Phi$ states, respectively. These avoided crossings can appreciably perturb the rovibrational levels and, consequently, further complicate the identification of the lines in the experimental spectra. Our calculated transition moments for all the computed electronic states are available at URL http://www.ita.uni-heidelberg.de/research/mld/.