Carbonyl–water Hydrogen Bonding: The H2CO-H2O Prototype

[[abstract]]The potential energy surface (PES) of the water–formaldehyde complex has been examined using ab initio methods. Three energetically low‐lying stationary points were located on the potential surface corresponding to one minimum and two transition states. All stationary points were examined using a double‐ζ plus polarization (DZP) basis set at the self‐consistent field (SCF), single and double excitation configuration interaction (CISD), and single and double excitation coupled‐cluster (CCSD) levels of theory. In addition, the minimum was more thoroughly investigated through the use of the triple‐ζ plus double polarization (TZ2P) basis set, the TZ2P plus higher angular momentum functions [TZ2P(f,d)] basis, and the TZ2P basis set augmented by a set of diffuse functions (TZ2P+diff) with those same theoretical methods. For each of the stationary points, geometrical parameters, absolute energies, classical binding energies, and zero‐point vibrational energy corrections are reported. Additional information concerning the minimum includes vibrational frequencies and corresponding infrared intensities, as well as predicted vibrational frequency shifts of the intramolecular frequencies for the complex and its deuterium substituted isotopomers