Potential constants for the hydrogen-bonded dimer H 2O⋯HF: Directional character of the hydrogen bond

Abstract

Vibrational wavenumbers obtained from IR and microwave spectroscopy have been used to determine the hydrogen-bond stretching and in-plane bending potential energy constants for the dimer H 2O…HF in the quadratic approximation. The stretching force constants f s = 735 ± 10 Nm −t and f σ = 17.4 ± 0.3 Nm −1 are reported while the preferred set of in-plane bending force constants are f θ(i)θ(i) = 2.52 × 10 −20 J rad −2 and f φ(i)φ(i) = 19.70 × 10 −20 J rad −2, where θ(i) and φ(i) refer to bending at the oxygen and hydrogen atoms, respectively. This provides the second example of a gaseous hydrogen-bonded dimer for which it is concluded that a bent hydrogen bond is energetically unfavourable by comparison with a linear hydrogen bond. The relative ease of in-plane and out-of-plane distortions of the hydrogen bond are correlated with OH⋯O configurations determined in the solid state.