KSEF R&D Excellence: Laser Spectroscopic Characterization of Transition Metal-Aromatic Compounds

Transition metal-aromatic complexes are widely used as catalysts in organic synthesis. A catalyst is a substance that initiates a desirable chemical reaction or speeds up a reaction that would otherwise be too slow to be economical. The most successful story is the metalloGenebased technology that has revolutionized a vital sector of the economy, the plastic industry. However, catalyst development is still carried out by trial and error, and rational design of new catalysts with predictable properties is a long-term goal requiring both basic and applied research. This work seeks to elucidate fundamental interactions between metal centers and aromatic molecules by studying electronic spectra and bonding of metal-aromatic complexes in the gas phase, where interferences from solvents and counterions are removed. The molecular systems involve group 3 (Sc, Y, La) and 4 (Ti, Zr, Ht) transition metal complexes of benzene and polycyclic aromatic hydrocarbons containing 2-4 benzene rings. The output of this research comprises ionization potentials, metal-ligand bond energies, vibrational frequencies, electron spin multiplicities, bonding configurations and molecular geometries of the complexes. This information is valuable for the study of reactive species in industrial processes and the understanding of metal-ligand interactions important in organometallic compounds, homogeneous catalysis and materials synthesis. We will use laser-assisted reactions to prepare metal compounds in supersonic jets, mass spectrometry to measure the abundance and distribution of reaction products, and laser spectroscopy to determine energy states and molecular structures. The major spectroscopic method is a high-resolution photoelectron technique, pulsed field ionization zero electron kinetic energy (ZEKE) spectroscopy. We have developed a ZEKE instrument that provides spectral resolution of tens of times better than that of conventional photoelectron methods. There is only one such kind ofthe instrument in Kentucky and are very few in the Nation. The success of this work will open a new area for high-resolution photoelectron spectroscopic applications and enhance Kentucky's emerging international reputation in this field. Moreover, the work will promote training and education in modem physical chemistry. Key words: ZEKE, photoelectron, laser spectroscopy, gas phase, and metal complexes.