Structure Determination of Anionic Metal Clusters via Infrared Resonance Enhanced Multiple Photon Electron Detachment Spectroscopy

We report vibrational spectra of anionic metal clusters, measured via electron detachment following resonant absorption of multiple infrared photons. To facilitate the sequential absorption of the required large number of photons, the cluster beam interacts with the infrared radiation inside the cavity of a free electron laser. Far-infrared spectra of the bare metal cluster anion Nb-10(-) as well as of the Nb6C- anion are measured in the 130-1000 cm(-1) range. The structures of these clusters can be unambiguously determined by comparison with calculated spectra of the putative global minima structures, identified by density functional theory calculations.