Real-Time Observation of Molecular Motion on a Surface
Ellen H. G. Backus,1
Andreas Eichler,2
Aart W. Kleyn,1,3
Mischa Bonn1,4
The laser-induced movement of CO molecules over a platinum surface
was followed in real time by means of ultrafast vibrational
spectroscopy. Because the CO molecules bound on different surface
sites exhibit different C–O stretch vibrational frequencies,
the site-to-site hopping, triggered by excitation with a laser
pulse, can be determined from subpicosecond changes in the vibrational
spectra. The unexpectedly fast motion—characterized by
a 500-femtosecond time constant—reveals that a rotational
motion of the CO molecules, rather than pure translation, is
required for this diffusion process. This conclusion is corroborated
by density functional theory calculations.
2 Institut für Materialphysik and Center for Computational Materials Science, Universität Wien, Sensengasse 8/12, A-1090 Wien, Austria.
3 Stichting voor Fundamenteel Onderzoek der Materie (FOM) Institute for Plasma Physics Rijnhuizen, Post Office Box 1207, 3430 BE Nieuwegein, Netherlands.
4 FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, Netherlands.
