TY  - JOUR
A1  - Oberg, H.
A1  - Gladh, Jörgen
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Katayama, T.
A1  - Kaya, Sarp
A1  - LaRue, Jerry
A1  - Mogelhoj, Andreas
A1  - Nordlund, Dennis
A1  - Ogasawara, Hirohito
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Florian
A1  - Turner, Joshua J.
A1  - Wolf, Martin
A1  - Wurth, W.
A1  - Ostrom, Henrik
A1  - Nilsson, Anders
A1  - Norskov, Jens K.
A1  - Pettersson, Lars G. M.
T1  - 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
JF  - Surface science
N2  - 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.
KW  - CO desorption
KW  - Potential of mean force
KW  - Two-temperature model
KW  - Pump-probe
KW  - X-ray spectroscopy
KW  - Density functional theory
Y1  - 2015
U6  - https://doi.org/10.1016/j.susc.2015.03.011
SN  - 0039-6028
SN  - 1879-2758
VL  - 640
SP  - 80
EP  - 88
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Schreck, Simon
A1  - Föhlisch, Alexander
T1  - Free-electron laser based resonant inelastic X-ray scattering on molecules and liquids
JF  - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
N2  - The unprecedented beam properties of free-electron laser based X-ray sources enable novel resonant inelastic X-ray scattering (RIXS) experiments. Femtosecond time-resolved RIXS can be used to follow charge, spin and structural dynamics of dilute solute molecules in solution. Ultrashort X-ray pulses allow probing of highly radiation sensitive states of matter such as the metastable phase of supercooled liquid water. Nonlinear X-ray probes like amplified spontaneous emission and stimulated resonant X-ray scattering provide an enhanced selectivity and sensitivity as well as a path to control radiation damage and increase the photon yields in RIXS experiments. (C) 2015 Elsevier B.V. All rights reserved.
KW  - Free-electron laser
KW  - RIXS
KW  - Pump-probe
KW  - Nonlinear X-ray spectroscopy
KW  - Molecules
KW  - Liquids
Y1  - 2015
U6  - https://doi.org/10.1016/j.elspec.2015.08.012
SN  - 0368-2048
SN  - 1873-2526
VL  - 204
SP  - 345
EP  - 355
PB  - Elsevier
CY  - Amsterdam
ER  -