title: Broadband femtosecond sum-frequency spectroscopy of CO on Ru1010 in the frequency and time domains.
abstract: CO on Ru[1010] was investigated by broadband femtosecond sum-frequency spectroscopy at 200 K. Approximately half of the frequency shift of 71 cm(-1) over the coverage range from 0.15 to 1.22 monolayers is shown to originate from dipole-dipole coupling, with the remainder due to a chemical shift. Despite low adlayer-surface registration at the highest coverages, the linewidth of the C-O stretch is comparatively low, and is described by homogeneous broadening according to sum-frequency free-induction decay measurements in the time domain. This can be explained by the dominance of the CO dipole coupling strength over the static disorder present in a coincidence structure. As the coverage decreases below 0.3 monolayer, the linewidth increases considerably, indicative of inhomogeneous broadening. Supported by a concomitant frequency change we suggest that at low coverages CO molecules form chains of irregular length in the [0001] direction, as has been shown for other surfaces with similar symmetry.
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Jonathan P R
authors.initials: JP
authors.lastname: Symonds
authors.forename: Heike
authors.initials: H
authors.lastname: Arnolds
authors.forename: Vanessa L
authors.initials: VL
authors.lastname: Zhang
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Fukutani
authors.forename: David A
authors.initials: DA
authors.lastname: King