Phillip Sheridan, PhD Associate Professor
PhD, University of Arizona
Teaching areas include general and physical chemistry. Research interests are in high-resolution electronic spectroscopy of small metal-containing radicals, synthesized in the gas phase, in order to characterize their electronic, bonding and geometric properties.
Metals play a central role in the function of many chemical systems. For example, they occupy the active sites of many biologically important molecules and act as catalytic surfaces for hydrogenation and polymerization reactions. In many cases, the interaction of the metal with the surrounding atoms is not well understood. The characterization of small metal-containing molecules can serve as a fundamental model for understanding the metal-ligand bonding interaction and structure in these larger systems (see figure 1).
The research in Dr. Sheridan’s group focuses on determining the electronic and geometric properties of small metal-containing molecules by high-resolution electronic spectroscopy. In general, these species are chemically unstable radicals consisting of a metal atom (for example Ca) bonded to a single ligand (CH3, CCH, NH2, etc.). The study of these molecules requires extreme laboratory conditions, in particular a low pressure reaction chamber. To this end, we are currently constructing a high resolution laser-ablation/molecular-jet laser spectrometer system, as shown in figure 2. A block diagram of the entire spectrometer system and the reaction chamber are shown in figures 3 and 4, respectively.
The molecules are synthesized repetitively in the nozzle assembly located inside the reaction chamber (see figure 4) by the reaction of ablated metal atoms with an appropriate reactant gas. Once created the molecules expand into the low pressure chamber as a cold molecular jet, travel down towards the vacuum pump, and are then probed by a laser (see figure 5). Any molecular fluorescence is then recorded using a photomultiplier tube (PMT). A spectrum of total fluorescence intensity vs. probe laser wavelength is then generated and subsequently analyzed to extract electronic and geometric information.