期刊
SURFACE SCIENCE
卷 640, 期 -, 页码 80-88出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.susc.2015.03.011
关键词
CO desorption; Potential of mean force; Two-temperature model; Pump-probe; X-ray spectroscopy; Density functional theory
资金
- U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-AC02-76SF00515]
- U.S. Department of Energy, Basic Energy Science through the SUNCAT Center for Interface Science and Catalysis
- Swedish Research Council [621-2011-4223]
- Danish Center for Scientific Computing
- Volkswagen Foundation
- Alexander von Humboldt Foundation
- Lundbeck Foundation
- LCLS
- Stanford University through the Stanford Institute for Materials Energy Sciences (SIMES)
- Lawrence Berkeley National Laboratory (LBNL)
- University of Hamburg through the BMBF priority program FSP 301
- Center for Free Electron Laser Science (CFEL)
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 similar to 2000K. 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 (similar to 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. (C) 2015 Elsevier B.V. All rights reserved.
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