Stimulated Emission Pumping Spectroscopyof the [X̃]A‘ State of CHF

We have recorded stimulated emission pumping (SEP) spectra of the ùA‘ ‘ → X̃¹A‘ system of CHF, which reveal rich detail concerning the rovibronic structure of the X̃¹A‘ state up to ∼7000 cm^-1 above the vibrationless level. Using several intermediate ùA‘ ‘ state levels, we obtained rotationally resolved spectra for 16 of the 33 levels observed in our previous single vibronic level (SVL) emission study (Fan et al., J. Chem. Phys. 2005, 123, 014314), in addition to one new level. An anharmonic effective Hamiltonian model poorly reproduces the term energies even with the improved set of data because of the extensive interactions among levels in a given polyad (p) having combinations of ν₁, ν₂, ν₃, which satisfy the relationship p = 2ν₁ + ν₂ + ν₃. However, the precise A rotational constants determined from the SEP data were invaluable in clarifying the assignments for these strongly perturbed levels, and the data are well reproduced using a multiresonance effective Hamiltonian model. The derived vibrational parameters are in good agreement with high level ab initio calculations. The experimental frequencies were combined with those of CDF to derive a harmonic force field and average (r_z,) structures for the ground state.