Element-Specific and Real-Time Observation of CO-Ru Chemisorption Bond Breaking with Soft X-ray Spectroscopy

March 2013 SSRL Science Summary by Lori Ann White, SLAC Office of Communications

An international collaboration of scientists, including several from SSRL, has taken advantage of the broad range of photon science capabilities available at the lab to investigate a proposal that adsorption and desorption of a molecule to a surface - both fundamental processes of interfacial chemistry - proceed through a transient "precursor" state in which the molecule is weakly bound to the surface. Their research focused on carbon monoxide adsorption/desorption on metal surfaces; although a large number of spectroscopic studies have been devoted to this reaction, the precursor state had never before been seen.

The researchers used a next-generation experimental setup developed at SSRL for both x-ray emission spectroscopy and x-ray absorption spectroscopy. The setup was equipped with a high-throughput compact grazing incidence grating spectrometer developed by Dennis Nordlund, Hirohito Ogasawara and Anders Nilsson. They started at SSRL Beam Line 13-2, first commissioning the setup and taking a static preparatory measurement of the CO-Ru chemisorption bond for the study.

Then the team transported the setup to LCLS to probe the short-lived precursor state. They observed electronic structure changes consistent with a weakening of the CO interaction with the substrate, but without significant desorption. A large fraction of the molecules (30%) were trapped in a transient precursor state that preceded desorption. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals.

 

Primary Citation

M. Dell'Angela, T. Anniyev, M. Beye, R. Coffee, A. Föhlisch, J. Gladh, T. Katayama, S. Kaya, O. Krupin, J. LaRue, A. Møgelhøj, D. Nordlund, J. K. Nørskov, H. Öberg, H. Ogasawara, H. Öström, L. G. M. Pettersson, W. F. Schlotter, J. A. Sellberg, F. Sorgenfrei, J. J. Turner, M. Wolf, W. Wurth and A. Nilsson, "Real-Time Observation of Surface Bond Breaking with an X-ray Laser", Science 339, 1302 (2013)

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Contacts

Hirohito Ogasawara, Stanford Synchrotron Radiation Lightsource
Dennis Nordlund, Stanford Synchrotron Radiation Lightsource
Anders Nilsson, Stanford Synchrotron Radiation Lightsource and SUNCAT