CO 2 Binding at Gold Cluster Cations: An Infrared Free‐Electron Laser Spectroscopic Investigation

Understanding the fundamental binding motifs of carbon dioxide is key to its efficient sequestration and/or molecular activation. In this context, gas‐phase metal clusters represent key model systems for the design of next generation materials. Infrared spectroscopy, especially using free‐electron lasers, provides a direct probe of molecular structure across a range of wavelengths inaccessible by tabletop light sources. Here, we report the investigation of CO 2 binding to isolated gold cluster cations, Au n + ( n = 4–11), using the FELICE light source, with structural assignments aided by quantum chemical calculations. In order to capture the well‐known Fermi dyad arising from resonance between the symmetric stretch and the overtone of the bend, an anharmonic vibrational treatment has been employed. Binding to a gold cluster cation only weakly perturbs the CO 2 which retains its linear geometry. Coordination occurs exclusively via an oxygen atom and a single gold atom of the cluster (η 1 ‐O), with very weak molecular activation observed. Successive CO 2 molecules bind in similar fashion to the first leading to multiply‐solvated clusters.