Dissociation Energy of the H₂O···HF Dimer

Even though (H₂O)₂ and (HF)₂ are arguably the most thoroughly characterized prototypes for hydrogen bonding, their heterogeneous analogue H₂O···HF has received relatively little attention. Here we report that the experimental dissociation energy ( D₀) of this important paradigm for heterogeneous hydrogen bonding is too large by 2 kcal mol^-1 or 30% relative to our computed value of 6.3 kcal mol^-1. For reference, computational procedures similar to those employed here to compute D₀ (large basis set CCSD(T) computations with anharmonic corrections from second-order vibrational perturbation theory) provide results within 0.1 kcal mol^-1 of the experimental values for (H₂O)₂ and (HF)₂. Near the CCSD(T) complete basis set limit, the electronic dissociation energy for H₂O···HF is ∼4 kcal mol^-1 larger than those for (H₂O)₂ and (HF)₂ (∼9 kcal mol^-1 for the heterogeneous dimer vs ∼5 kcal mol^-1 for the homogeneous dimers). Results reported here from symmetry-adapted perturbation theory computations suggest that this large difference is primarily due to the induction contribution to the interaction energy.