Accurate Density Functional Calculations of Core Electron Binding Energies on Hydrogen-Bonded Systems

We present a quantum chemical investigation of core−electron binding energies (CEBEs) for small hydrogen-bonded clusters involving water, carboxylic acids, and formamide. Our DFT Δ E KS method well reproduces scarce experimental CEBEs available in the literature, especially the recent ones on gas phase water clusters. This shows that hydrogen bonds are actually detectable using XPS, even though it is a core level probing technique. This may be of major interest for hydrogen bonding detection in very thin layers, for which few methods may have the required sensitivity. A correlation is further established between hydrogen bond lengths in the cluster and binding energy shifts, as a function of cluster size. Unlike what is concluded for rare gas clusters, these shifts may be uniquely connected to intramolecular geometrical rearrangements, rather than collective spherical-type relaxation effects. This may also lead to the possibility of a direct measure of mean bond lengths in associated materials (solid, liquid, or gas) using XPS.