A global ab initio potential energy surface for formaldehyde

We report a global potential energy surface for formaldehyde. The surface is a combination of six local fits joined smoothly by five switching functions. The fits are to roughly 80000 CCSD(T)/aug-cc-PVTZ and 53000 MR-CI/aug-cc-PVTZ calculations of electronic energies. The surface describes the H2CO minimum, the cis and trans HCOH isomers, the molecular channel, H-2+CO, and the radical channel, H+HCO. The properties of the potential are evaluated by analyzing the properties of the six stationary points, one-dimensional cuts, and contour plots of the fit.