The rotational contour of the band at 22433 cm -1 was simulated using the PGOPHER software package . The molecular parameters predicted by the CCSD calculations were used to define the ground state rotational constants. Based on the computed structures, energies, and oscillator strengths, 3 2 A² appears to be the only viable assignment for the excited state. The computed vertical excitation energy for the 4 2 A' state also falls into this region. However, the structure of the 4 2 A' state is quite different from the ground state. The computed O-Th-F angle of 91° for the 4 2 A' state is much smaller than the value of 112° for the ground state, and the geometry relaxation energy is large, on the order of 3000 cm -1 . These properties exclude the 4 2 A' state as a plausible candidate state. Note that the prediction that the upper state of the 22433 cm -1 band has a similar equilibrium geometry to that of the ground state was supported by the associated DLIF spectrum shown in Fig. . The dominance of the emission back to the ground state zero-point level was consistent with an almost diagonal distribution of Franck-Condon factors. The weak transitions to vibrationally excited lower levels defined energies of 850 (1,0,0), 134 (0,1,0), and 538 (0,0,1) cm -1 , in reasonable agreement with the CCSD harmonic frequency values given in Table . Most of the remaining discrepancies can be attributed to corrections due to triple excitations. The corresponding CCSD(T) harmonic frequencies amount to 854, 137, and 545 cm - 1 , respectively. The anharmonic contributions play a relatively minor role; vibrational second-order perturbation theory calculations give anharmonic corrections of -1, -4, and -4 cm -1 . The CCSD(T) fundamental frequencies thus take values of 853, 133, and 541 cm -1 . They compare favorably with the measured values.