Electronic structure effects from hydrogen bonding in the liquid phase andin chemisorption: an integrated theory and experimental effort

A closely integrated theoretical and experimental effort to understand chem ical bonding using X-ray spectroscopic probes is presented. Theoretical tec hniques to simulate XAS (X-ray absorption spectroscopy), XES (X-ray emissio n spectroscopy), RIXS (resonant inelastic X-ray scattering) and XPS (X-ray photoelectron spectroscopy) spectra have been developed and implemented wit hin a density functional theory (DFT) framework. In combination with new ex perimental techniques, such as high-resolution XAS on liquid water under am bient conditions and XES on complicated surface adsorbates, new insight int o e.g. hydrogen-bonded systems is obtained. For the (3 x 2) overlayer struc ture of glycine/Cu(110), earlier work has been extended to include adsorbat e-adsorbate interactions. Structures are optimized for large cluster models and for periodic boundary conditions. It is found that specific features i n the spectra arise from hydrogen-bonding interactions, which thus have imp ortant effects at the molecular-orbital level. XAS on liquid water shows a pronounced pre-edge feature with significant intensity, while the spectrum of ice shows only little intensity in this region. Theoretical spectrum cal culations, based on instantaneous structures obtained from molecular-dynami cs (MD) simulations, show that the pre-edge feature in the liquid is caused by water molecules with unsaturated hydrogen bonding. Some aspects of the theoretical simulations will be briefly discussed.