Ionization potentials for the HCO trimer.

In this work, a computational study on the ionization potentials (IPs) of the formaldehyde trimer, (HCO), is presented. Twelve lowest-lying vertical IPs were determined through the use of the coupled-cluster level of theory using correlation consistent basis sets with extrapolation to the complete basis set limit and consideration of core electron correlation effects. Specifically, the equation-of-motion ionization potential coupled-cluster with single and double excitations method with the aug-cc-pVnZ and aug-cc-pCVnZ (n = D and T) basis sets was used. The Feller-Peterson-Dixon (FPD) composite approach was employed to provide accurate IPs, and eight conformations of (HCO) were considered. The FPD IPs determined for (HCO) were found to be systematically lower than those computed for the dimer and monomer of HCO in the pattern IP > IP > IP for a given IP. In addition, the IPs calculated when considering only the more stable conformation (C) are in good agreement with those obtained using the eight conformations of the HCO trimer, and thus, the actual conformation played only a minor role in determining such properties in the present case. By providing first accurate IP results for the HCO trimer, we hope to motivate future experimental and computational investigations (e.g., studies involving photoionization) that rely on such quantities.