The equipment used for these experiments has been described previously . Gas-phase OThF was obtained by pulsed laser ablation (1064 nm light) of a Th rod in the presence of a pulse of He carrier gas. The latter contained 0.4% SF6 and 0.4% O2 to provide the oxidants needed for the formation of OThF. The He-entrained reaction products were supersonically expanded into vacuum chambers where the spectra were acquired. LIF and DLIF spectra were recorded with the excitation laser beam set to cross the jet expansion approximately 7.5 cm downstream from the nozzle orifice. LIF was collected along an axis that was perpendicular to both the laser beam axis and the jet expansion axis. For the recording of LIF data, a long-pass filter was used to reduce the scattered laser light, and the filtered fluorescence was detected by a photomultiplier tube (Photonis XP2020). Fluorescence decay curves, acquired using a digital oscilloscope (LeCroy WaveSurfer 24Xs) to signal average 500 laser pulses per trace, were measured using the same set-up. DLIF spectra were obtained when the long-pass filter was replaced by a 0.25 m monochromator (Jarrell-Ash 82-410).