Laser spectroscopy on the A0-X1Σ transition of T1I

The first excited electronic state of TII was investigated by laser excitation and laser fluorescence spectroscopy. Almost completely resolved rotational fine structure was observed with the help of a collimated molecular beam and a single-mode cw dye laser. From the derived Dunham parameters Y_lk a RKR potential for the excited state is calculated. The unusual shape of the potential energy curve can be understood as originating from an avoided crossing of the ionic ground-state potential and a non-bonding covalent state of the atomic asymptote (6p) ²P_1/2(TI)+(5p)^{5 2}P_3/2(I).