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Originally published in Science Express on 10 November 2005
Science 16 December 2005:
Vol. 310. no. 5755, pp. 1790 - 1793
DOI: 10.1126/science.1120693
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Reports

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.

1 Leiden Institute of Chemistry, Leiden University, Post Office Box 9502, 2300 RA Leiden, Netherlands.
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.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)