Laser photoluminescence of TiO in Ne at 4 °K

Pseudo-gas-phase photoluminescence spectra of TiO isolated in Ne matrices at 4 °K have been obtained. Photoluminescence is induced by laser excitation from the X 3Δ ground state to B 3Π and C 3Δ electronic levels using a cw tunable dye laser and a cw argon ion laser, respectively. Red emission from B 3Π vibrational levels terminating in ground state levels is observed. In addition, the B 3Π (v=0) and B 3Π (v=1) levels have been found to undergo matrix-induced intersystem relaxation into the b 1Π state. Near-infrared emission between excited states in the singlet manifold of TiO has been observed and identified as belonging to the δ (b 1Π→a 1Δ) and the φ (b 1Π→d 1Σ+) band systems. Observed δ and φ emission bands are uniformly shifted by −93 cm−1 and +73 cm−1, respectively, from observed or predicted gas phase bandheads. The line shape of the δ and φ emission in the solid is that of a sharp zero-phonon line accompanied by a broad multiphonon sideband. An additional sharp zero-phonon emission system, here labeled the ζ system, is found to overlap several broad multiphonon bands of the red γ′ (B 3Π→X 3Δ) emission. Evidence obtained supports the tentative conclusion that the ζ system is due to intercombination b 1Π→X 3Δ emission. From the assigned intercombination transition the energy of the low-lying a 1Δ state is determined to be 3500 cm−1 above the X 3Δ ground state. The 3500 cm−1 value for the relative energy between the isoconfigurational a 1Δ and X 3Δ states is in qualitative agreement with theoretical expectations based on consideration of the bonding in the TiO molecule.