The E ³Π-X ³Δ transition of jet-cooled TiO observed in absorption

The (0, 0) and (1, 0) bands of the E ³Π-X ³Δ transition of TiO in the near-infrared have been recorded by frequency modulated laser absorption spectroscopy in a laser ablation/free jet expansion source. The observed linewidths (FWHM) varied from 300 to 500 MHz according to the expansion conditions and are dominated by residual Doppler broadening in the unskimmed source. Data for the (0, 0) band have been obtained for TiO molecules containing all the naturally occurring Ti isotopes but, for the weaker (1, 0) band, only for ⁴⁸TiO. Rotational constants for the two upper state vibrational levels were derived by fitting the data to an effective Hamiltonian; equilibrium parameters have been calculated. The experimental results are compared to the results of ab initio calculations on the E-X system. Ab initio results for the b-a system and for the lowest ³Σ⁻ state are also presented. They indicate that the D ³Σ⁻ state is not a very low-lying state.