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Zusammenfassung:
We present an experimental and theoretical study of the structure of small, neutral gold clusters
– Au3, Au4, and Au7 – “tagged” by krypton atoms. Infrared (IR) spectra of AuN·KrM complexes
formed at 100 K are obtained via far-IR multiple photon dissociation in a molecular beam. The
theoretical study is based on a statistical (canonical) sampling of the AuN·KrM complexes through
ab initio molecular dynamics using density-functional theory in the generalized gradient approximation,
explicitly corrected for long-range van-der-Waals interactions. The choice of the functional
is validated against higher-level first-principle methods. Thereby finite-temperature theoretical vibrational
spectra are obtained that are compared with the experimental spectra. This enables us
to identify which structures are present in the experimental molecular beam for a given cluster
size. For Au2, Au3, and Au4, the predicted vibrational spectra of the Kr-complexed and pristine
species differ. For Au7, the presence of Kr influences the vibrational spectra only marginally. This
behavior is explained in terms of the formation of a weak chemical bond between Kr and small
gold clusters that localizes the Kr atom at a defined adsorption site, whereas for bigger clusters the
vdW interactions prevail and the Kr adatom is delocalized and orbits the gold cluster. In all cases,
at temperatures as low as T = 100 K, vibrational spectra already display a notable anharmonicity
and show, in comparison with harmonic spectra, different position of the peaks, different intensities
and broadenings, and even the appearance of new peaks.
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