Accurate density functional calculations of core electron binding energieson hydrogen-bonded systems

We present a quantum chemical investigation of core-electron binding energi es (CEBEs) for small hydrogen-bonded clusters involving water, carboxylic a cids, and formamide. Our DFT DeltaE(KS) method well reproduces scarce exper imental CEBEs available in the literature, especially the recent ones on ga s phase water clusters. This shows that hydrogen bonds are actually detecta ble using XPS, even though it is a core level probing technique. This may b e of major interest for hydrogen bonding detection in very thin layers, for which few methods may have the required sensitivity. A correlation is furt her established between hydrogen bond lengths in the cluster and binding en ergy shifts, as a function of cluster size. Unlike what is concluded for ra re gas clusters, these shifts may be uniquely connected to intramolecular g eometrical 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.