Strength of the Benzene−Water Hydrogen Bond

Very large basis set, correlated calculations of the benzene−water complex predict a geometry in which the water molecule sits above the aromatic ring with oxygen pointed away from the benzene center of mass. The purely electronic binding energy, in the complete basis set limit, was found to be −3.9 ± 0.2 kcal/mol, or only 20% weaker than the water−water interaction. When zero-point energies are included, the ΔE0(0 K) values are identical within their estimated uncertainties. Core/valence and higher-order correlation recovery via coupled cluster calculations were found to play a minor role. The present ΔE0(0 K) value of −2.9 ± 0.2 kcal/mol is in good agreement with a recent threshold photoionization experiment that yielded −2.4 ± 0.1 kcal/mol.