High-resolution FTIR spectroscopy and analysis of the Ka = 0 ← 1 subbands of the fundamentals ν3 and ν6 of the dimer (HF)2

We report new far-infrared spectra of (HF)2 obtained by high resolution long-path Fourier Transform-Infrared (FTIR) spectroscopy. The origins of the two tunneling components of the Ka= 0 ← 1 subband of the in-plane symmetric bending fundamental ν3 were found to be at 450.4546 cm−1 (Γt: A+ ← B+) and at 451.4583 cm−1 (B+ ← A+), and of the Ka= 0 ← 1 subband of the out-of-plane bending fundamental ν6 at 382.0802 cm−1 (A+ ← A+) and at 383.2245 cm−1 (B+ ← B+). The Ka= 0 term values with respect to the ground state Γt = A+ term are 486.9442 cm−1 for the A+ and 486.8834 cm−1 for the B+ tunneling levels of ν3. They are 417.5053 cm−1 for the A− and 419.7140 cm−1 for the B− vibration-tunneling sublevels of ν6. The results are discussed in relation to full-dimensional quantum dynamics and predictions based on recent ab initio calculations and our empirically refined potential energy hypersurfaces. Graphical abstract.