Infrared spectroscopy to probe structure and dynamics in metal ion–molecule complexes

Vibrational spectroscopy measurements are described for mass-selected metal cation–molecular complexes using the technique of infrared resonance-enhanced photodissociation (REPD) spectroscopy. We discuss the mechanism of the REPD process in the infrared and how multiphoton techniques or rare gas tagging can be employed to facilitate dissociation processes in strongly bound complexes. Spectra are reported for Fe(CO2)n complexes that demonstrate the formation of coordination spheres around the metal cation and for Mg(CO2)n complexes, where the interaction with theory makes it possible to obtain structures for small clusters. Both of these studies investigate the asymmetric stretch region of CO2. Ni(C2H2)n complexes are studied in the C–H stretch region, demonstrating evidence for intracluster cyclization reactions. Finally, experiments are described for metal ion–benzene (M1⁄4V, Al) complexes excited in the benzene ring distortions and C–H bending region. These experiments confirm the p-bonded configuration of these complexes.