Associate Professor Doreen Leopold

CSENG Chemistry
College of Science & Engineering
Twin Cities
Project Title: 
Metal Cluster Structures and Reactivities: Computational Analysis of Anion Photoelectron Spectra

Research in this group focuses on the chemical bonding between transition metals in dimers, trimers, and small clusters, and their reactivities with gas phase molecules. Experiments in this laboratory employ anion photoelectron spectroscopy, flow tube ion-molecule chemistry, and mass spectrometry to study negative ions and neutral molecules. To help assign the photoelectron spectra, the researchers compare the experimental results with those calculated using density functional (DFT) methods. These DFT calculations are used to predict the equilibrium geometries, vibrational frequencies, electronic state energies, and spin multiplicities of the ground and low lying electronic states of the anionic and neutral systems. By simulating the Franck-Condon photodetachment spectra based upon the DFT results and directly comparing those predictions for possible electronic states and (for polyatomics) different isomers 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.

Current work includes studies of bare diatomics incorporating transition metals from Groups 5 and/or 6, which can exhibit very high multiple bond orders. 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. The group's research also includes studies of organometallic complexes produced upon reaction of transition metals with simple hydrocarbons, such as ethylene, butadiene, and benzene. These results can enrich our understanding of the relationships between the chemical reactivities of transition metal species and the properties of their ground and low-lying electronic states. In a broader context, these studies can help to elucidate the mechanisms of catalytic processes mediated by transition metal systems. They can also provide useful benchmarks to aid in the further development, by computational chemists, of improved methods with which to treat the computationally challenging ground and excited electronic state properties of of bare transition metal clusters and coordinatively unsaturated organometallics.

Project Investigators

Melissa Baudhuin
Associate Professor Doreen Leopold
Alex Schnepper
 
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