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.