The IE of OThF was determined by observation of the two-color photoionization efficiency curve. For this measurement the first laser was set to excite the OThF 22433 cm -1 band, and a second laser was scanned over the energy range where the sum of the photon energies would be sufficient for ionization. The onset of ionization was observed for second photon energies over the range 28090 -28170 cm -1 . The mid-point yielded a threshold energy of 28130±40 cm -1 . When corrected for the electric field of the mass spectrometer (115 cm -1 red-shift ) this measurement provided an IE of 50678±40 cm -1 (6.283(5) eV).