High resolution interferometric FTIR spectroscopy of (HF)2: analysis of a low frequency fundamental near 400 cm-1

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Abstract
The spectrum of (HF)2 was recorded under equilibrium conditions in a long path thermostated cell at a resolution of 0·02 cm-1 between 350 and 550 cm-1. We present the first rotational analysis of a subband of the low frequency fundamentals of the HF dimer. The subband origins for the two tunnelling components of the (v = 0, K = 0) → (v = 1, K = 1) transition were found to be at 400·7534 cm-1 (B + symmetry in the ground state) and at 399·7865 cm-1 (A + symmetry in the ground state). The transition is tentatively assigned to the torsional vibration. The tunnelling frequency between the two equivalent isomers of (HF)2 is 48·77 GHz for v = 1, K = 1, about a factor of 1·5 larger than in the ground state (v = 0, K = 1). The assignment of other subbands is also discussed.