Fundamental Reaction Mechanisms
March 10, 2009
The development of short-pulsed lasers has allowed for direct probing of chemical reactions in real time. Typically, one laser pulse is used to initiate a chemical reaction, and a second pulse is used to probe the intermediates or products some time later. Chemical reactions in condensed phases are especially well suited to these techniques, since the steps in the reactions occur very fast, usually on a time scale shorter than a nanosecond. My research focuses on the use of time-resolved techniques, both on the femtosecond/picosecond time scale, and on the longer nanosecond/microsecond time scale. Of particular importance is the use of infrared spectroscopy for probing chemical species, since it is easier to correlate with molecular structure than electronic spectroscopy. C-F bond activation reactions: One of our particular interests in my lab is the reactions involving organometallic species involved in catalytic bond breaking processes. Previous work on molecules which break C—H bonds in alkanes shows that the first photon dissociates a ligand from the metal center, and then this metal atom reacts with the surrounding alkane solvent molecule to form a alkyl hydride product, having broken a C—H bond in the alkane. Currently we are studying a related molecule that is able to break C—F bonds in perfluoro-benzene. This tungsten containing organometallic has a reaction between the W atom, and a tethered perfluorobenzene ring. Our recently published work showed that the rate of the reaction is limited by the formation of a weak complex with the solvent. We are able to measure the spectrum of this solvent complex on a nanosecond time-scale, and compare the spectrum directly with calculations. Laser surface patterning: In my lab we are also research novel methods for using lasers to functionalize surfaces. Working with Dr. Matt Linford, we are using high intensity laser pulses to ablate, of remove, atoms from the surface of silicon wafers. The newly exposed Si atoms react rapidly with molecules in liquid placed on the surface. Using an array of micro-lenses, we have shown rapid functionalization and patterning of surfaces with alkyl halides, epoxides, amines and other chemically important groups. Our current setup allows for the creation of 2500 spots each with a diameter of 2-3 microns. These spots can be functionalized with DNA, proteins or other chemical or biochemical sensors.