Theoretical Study of the Spectroscopy of TiO

Theoretical electronic transition moments are presented for all of the dipole-allowed transitions connecting the f 1 Δ, c 1 Φ, b 1 Π, d 1 Σ + , and a 1 Δ singlet states and the C 3 Δ, B 3 Π, A 3 Φ, E 3 Π, and X 3 Δ triplet states of TiO. The transition moments connecting the C 3 Δ state with lower states were determined at the complete active space self-consistent field (CASSCF) level, and the transition moments connecting the other states were determined at both the CASSCF and the internally contracted multireference configuration-interaction (IC-MRCI) level. The CASSCF active space can be made sufficiently large that the effect of electron correlation on the transition moments is included quantitatively. The theoretical radiative lifetimes for the short-lived states are generally within 10% of the recent laser fluorescence measurements of Hedgecock, Naulin, & Costes. For the v = 0 level of the E 3 Π state, we obtain a radiative lifetime of 4259 ns, consistent with their determination of τ v =0 > 2000 ns, but much longer than the lifetime of 770 ± 40 ns reported by Simard & Hackett. Except for the δ-bands, the theoretical oscillator strengths are less than those currently employed in molecular opacity calculations.