The infrared spectrum and internal rotation barrier in HF–BF3

The rotationally resolved infrared spectrum of the HF stretch fundamental in combination with one quantum of internal rotation excitation has been investigated for the HF–BF3 complex using a color-center-laser optothermal molecular-beam spectrometer. The infrared band origin is red-shifted by 3.9 cm−1 from the HF monomer origin. The magnitude of the Coriolis interaction in the m=±1 internal rotor state observed in combination with the HF stretch gives a barrier to internal rotation of 54 cm−1 in the HF stretch excited state.