Detection of the Thorium Dimer via Two-Dimensional Fluorescence Spectroscopy.

Thorium dimer, Th2, has been detected in the gas phase via two-dimensional laser-induced fluorescence electronic spectroscopy. The visible excitation spectra are broad, unstructured features with an approximate line width of 10 cm(-1). The spectrum consists of vibrational progressions associated with excitation from the ground electronic state to two different excited electronic states. The dispersed fluorescence was analyzed to give ground state vibrational constants ωe = 134.86 ± 0.66 cm(-1) and ωexe = 0.50 ± 0.04 cm(-1). Vibrational constants ωe = 169 ± 3 and 212 ± 2 cm(-1) were determined for the two excited electronic states. The radiative lifetimes were measured. A comparison with theoretical predictions is given.