Optical laser-induced CO desorption from Ru(0001) monitored with a 
free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor 
state

Öberg, H.; Gladh, J.; Dell'Angela, M.; Anniyev, T.; Beye, M.; Coffee, R.; Föhlisch, A.; Katayama, T.; Kaya, S.; LaRue, J.; Møgelhøj, A.; Nordlund, D.; Ogasawara, H.; Schlotter, W.F.; Sellberg, J.A.; Sorgenfrei, F.; Turner, J.J.; Wolf, Martin; Wurth, W.; Öström, H.; Nilsson, A.; Nørskov, J.K.; Pettersson, L.G.M.

doi:10.1016/j.susc.2015.03.011

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Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state

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Wolf, Martin
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Citation

Öberg, H., Gladh, J., Dell'Angela, M., Anniyev, T., Beye, M., Coffee, R., et al. (2015). Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state. Surface Science, 640, 80-88. doi:10.1016/j.susc.2015.03.011.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0026-C213-0

Abstract

We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (< 100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of ~ 2000 K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (~ 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate.