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 center dot center dot center dot HF has received relatively little attention. Here we report that the experimental dissociation energy (D-0) 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 D-0 (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 center dot center dot center dot HF is similar to 4 kcal mol(-1) larger than those for (H2O)(2) and (HF)(2) (similar to 9 kcal mol(-1) for the heterogeneous dimer vs similar to 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.