Metal Cluster Structures and Reactivities: Computational Elucidation of Anion Photoelectron Spectra
Research in this group focuses on the chemical bonding between transition metal atoms in ligand-free diatomics and clusters, and their reactivities with small gas phase molecules. Experiments in the laboratory employ anion photoelectron spectroscopy, flow tube ion-molecule chemistry, and mass spectrometry to study these anions and the corresponding neutral species. To help assign the photoelectron spectra, they compare the experimental results with those calculated using density functional methods, which are used to predict the equilibrium geometries, vibrational frequencies, electronic state energies, and spin multiplicities of the anionic and neutral systems. By simulating the Franck-Condon photodetachment spectra based upon the DFT results and comparing those predictions for possible electronic states and (for polyatomics) different isomers directly to the experimental spectra, the researchers are often able to deduce convincing assignments for the observed species, even if they have never been studied before either spectroscopically or computationally. The group's spectroscopic studies can also provide useful benchmarks to aid in the further development, by other researchers, of improved theoretical methods with which to treat these small but computationally challenging transition metal clusters and partially-ligated organometallics.
Current work includes studies of bare diatomics incorporating transition metals from Groups 5 and/or 6, which can exhibit very high-order multiple bonding. For example, the researchers are investigating the Group 6, third transition series homonuclear diatomic W2 (tungsten dimer), which has a formal bond order of 6, as well as the anions of bimetallic dimers incorporating metals from both Groups 5 and 6, such as NbCr-, NbMo- and NbW-, which can also exhibit sextuple bonds. They are also studying (or plan to study next year) organometallic complexes produced upon reaction of transition metal atoms with simple hydrocarbons (such as methane, ethylene or butadiene) or with CO2. These results can contribute to the understanding of the relationships between the chemical reactivities of various transition metals and the configurations and spin multiplicities of their ground and low-lying electronic states. In a broader context, these results can contribute to the development of an improved understanding of catalytic processes mediated by transition metal systems.
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