Infrared Spectroscopy of Niobium Oxide Cluster Cations in a Molecular Beam: Identifying the Cluster Structures

Infrared spectra of niobium oxide cluster cations are measured via IR multiple photon dissociation spectroscopy in the 400−1650 cm-1 region. The cluster cations are obtained directly from a laser vaporization source and irradiated with the infrared light emitted by a free electron laser. For those oxide clusters that fragment after excitation, the IR spectra are recorded by measuring the cluster intensity changes as a function of the IR wavelength. The spectra of all examined oxide clusters exhibit two main absorption features that can be assigned to vibrations of terminal (NbO) or bridging (Nb−O−Nb) oxide groups. For selected clusters DFT calculations at the B3LYP/LACVP* level have been performed and the calculated vibrational spectra are compared to the experimental data to identify the gas phase structures of the clusters.