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Journal Article

Ultrafast Adsorbate Excitation Probed with Subpicosecond-Resolution X-Ray Absorption Spectroscopy

We use a pump-probe scheme to measure the time evolution of the C K-edge x-ray absorption spectrum from CO/Ru(0001) after excitation by an ultrashort high-intensity optical laser pulse. Because of the short duration of the x-ray probe pulse and precise control of the pulse delay, the excitation-induced dynamics during the first picosecond after the pump can be resolved with unprecedented time resolution. By comparing with density functional theory spectrum calculations, we find high excitation of the internal stretch and frustrated rotation modes occurring within 200 fs of laser excitation, as well as thermalization of the system in the picosecond regime. The ∼100  fs initial excitation of these CO vibrational modes is not readily rationalized by traditional theories of nonadiabatic coupling of adsorbates to metal surfaces, e.g., electronic frictions based on first order electron-phonon coupling or transient population of adsorbate resonances. We suggest that coupling of the adsorbate to nonthermalized electron-hole pairs is responsible for the ultrafast initial excitation of the modes.

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Author(s)
Elias Diesen
Hsin-Yi Wang
Simon Schreck
Matthew Weston
Hirohito Ogasawara
Jerry LaRue
Fivos Perakis
Martina Dell'Angela
Flavio Capotondi
Luca Giannessi
Emanuele Pedersoli
Denys Naumenko
Ivaylo Nikolov
Lorenzo Raimondi
Carlo Spezzani
Martin Beye
Filippo Cavalca
Boyang Liu
Jörgen Gladh
Sergey Koroidov
Pieter S. Miedema
Roberto Costantini
Tony F. Heinz
Frank Abild-Pedersen
Johannes Voss
Alan C. Luntz
Anders Nilsson
Journal Name
Phys. Rev. Lett.
Publication Date
2021
DOI
10.1103/PhysRevLett.127.016802