Photoelectron and Photoionization Spectroscopy of Metal-Organic Complexes

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Dong-Sheng Yang of the University of Kentucky is supported by the Experimental Physical Chemistry Program to investigate the electronic spectra, metal-ligand binding, electronic states, and molecular structures of coordinatively unsaturated gaseous metal-organic complexes. The metal-organic systems include lithium, aluminum, scandium, and copper complexes of DNA and RNA nucleobases, polycyclic aromatic hydrocarbons, and polyphenyls. These complexes are prepared in laser-vaporization molecular beams, identified with photoionization mass spectrometry, and studied using ultraviolet (UV) and infrared (IR)-UV pulsed field ionization-zero electron kinetic energy (ZEKE) photoelectron and photoionization spectroscopy. The UV ZEKE experiments measure precise ionization energies and low frequency metal-ligand stretches and bends, whereas the IR-UV ZEKE and photoionization experiments determine the high-frequency ligand vibrational modes of these systems. The ionization energy is one of the key thermochemical properties of a molecule and is used to obtain the metal-ligand neutral bond energy by combining the ionization energy of the metal atom and the bond energy of the cation. The metal-ligand stretches and bends give direct evidence about the metal-ligand binding, whereas the high-frequency ligand vibrations probe changes in the ligand geometry induced by metal coordination. Combining the spectroscopic data and theoretical predictions determines electronic states and molecular structures. This research project will lead to new knowledge about the structure and energetics of complexes made up of metal atoms binding to molecules. The results will be of interest to practitioners in organometallic chemistry, biochemistry, catalysis, and materials synthesis. This project provides technologically challenging research training opportunities for students and postdoctoral associates to prepare them effectively for future employment.