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 (1997) for the most of the computed bands except for the delta and phi ones. For the delta band our computed electronic oscillator strength f(0) is 0.0581 which is considerably smaller than that of Langhoff (0.096). Our f(e) supports the proposal of Plez (1998) that the value of Langhoff should be divided by similar to2 to match observations. Our MRCI calculations give fa of 0.0668 for the phi band. This is larger than the value of 0.036 obtained by Langhoff. We adduce strong arguments that our f, for the phi 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/rssearch/mld/.