Far-IR Spectra and Structures of Small Cationic Ruthenium Clusters: Evidence for Cubic Motifs

Far-IR vibrational spectra of small ruthenium cluster cations (Ru₇⁺, Ru₈⁺, and Ru₉⁺) are measured via infrared multiple photon dissociation (IR-MPD) spectroscopy using Ar atoms as messenger for the absorption. These spectra are compared to results from density functional theory calculations, leading to structural assignments. The pure functional PBE leads to better agreement with the experimental data compared to the hybrid functional PBE0. For all three cluster sizes the structures assigned are based on a cubic motif and are a distorted cube missing one corner atom (Ru₇⁺), a slightly distorted cube (Ru₈⁺), and a face-capped cube (Ru₉⁺)