title: Charge-induced dipole vs. relativistically enhanced covalent interactions in Ar-tagged Au-Ag tetramers and pentamers.
abstract: Vibrational spectra of Au(n)Ag(m)(+)⋅Ar(k) (n + m = 4, 5; k = 1-4) clusters are determined by far-infrared resonant multiple photon dissociation spectroscopy in the range ν̃=100-250 cm(-1). The experimental spectra are assigned using density functional theory for geometries obtained by the Birmingham cluster genetic algorithm. Putative global minimum candidates of the Ar complexes are generated by adding Ar atoms to the Au(n)Ag(m)(+) low energy isomers and subsequent local optimization. Differential Ar binding energies indicate exceptionally strong Au-Ar bonds in Au-rich clusters, leading to fundamental changes to the IR spectra. The stronger Ar binding is attributed to a relativistically enhanced covalent character of the Au-Ar bond, while in Au-rich species charge-induced dipole interactions overcompensate the relativistic affinity to Au. Moreover, not only the absolute composition but also the topologies are essential in the description of Ar binding to a certain cluster.
authors.affiliation: Eduard-Zintl-Institut, Technische Universität Darmstadt, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Shayeghi
authors.affiliation: Eduard-Zintl-Institut, Technische Universität Darmstadt, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Schäfer
authors.affiliation: National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
authors.forename: D M
authors.initials: DM
authors.lastname: Rayner
authors.affiliation: School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: R L
authors.initials: RL
authors.lastname: Johnston
authors.affiliation: Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Fielicke