Article,
Observation of Uncorrelated Microscopic Motion in a Strongly Interacting Adsorbate System
J. Am. Chem. Soc., (2008)
DOI: 10.1021/ja800118x
Abstract
Modeling of intermolecular forces is a central theme in the physical
sciences. The prototypical heterogeneous catalysis system, CO/Pt(111),
is an extensively studied example where strong pairwise repulsive
forces between the CO molecules have been used to explain the observed
structure and dynamics. No direct measurements of these forces were
available; yet, they offered a natural way of explaining various
macroscopic observations assuming a separable adsorbate-substrate
interaction and pairwise adsorbate-adsorbate interactions. In the
present study, we measure intermolecular forces by following CO motion
on a microscopic scale. The uncorrelated dynamics we observe throughout
the coverage range of the measurements excludes the existence of
the strong pairwise forces previously suggested. The increase in
the rate of uncorrelated motion is explained by a nonlocal modification
of the adsorbate-substrate interaction, reflecting a many-body system
that cannot be described by the standard separable interaction approach.
