Dissociation Energy of the H 2 O· · · 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, 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 approximately 4 kcal/mol larger than those for (H2O)2 and (HF)2 (~9 kcal/mol for the heterogeneous dimer vs. ~5 kcal/mol for the homogeneous dimers). Results reported here from symmetry adapted perturbation theory (SAPT) computations suggest that this large difference is primarily due to the induction contribution to the interaction energy.