Theoretical Study of the Spectroscopy of TiO

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Abstract
Theoretical electronic transition moments are presented for all of the dipole-allowed transitions connecting the f1Δ, c1Φ, b1Π, d1Σ+, and a1Δ singlet states and the C3Δ, B3Π, A3Φ, E3Π, and X3Δ triplet states of TiO. The transition moments connecting the C3Δ 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 E3Π state, we obtain a radiative lifetime of 4259 ns, consistent with their determination of τv=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.