title: Real-time observation of molecular motion on a surface.
abstract: 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.
authors.affiliation: Leiden Institute of Chemistry, Leiden University, Post Office Box 9502, 2300 RA Leiden, Netherlands.
authors.forename: Ellen H G
authors.initials: EH
authors.lastname: Backus
authors.forename: Andreas
authors.initials: A
authors.lastname: Eichler
authors.forename: Aart W
authors.initials: AW
authors.lastname: Kleyn
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn