Research Interest:

In our surface experiments atomic radical beams are scattered from and/or reacted with clean, well characterized(e.g. using LEED, Auger, and He diffraction) single crystal (or amorphous) surfaces. Atomic radicals are generated by photodissociating diatomic molecules and relying on kinematics to propel the desired atoms towards the surface. These intense, pulsed beams are short (~ 150 nanoseconds) and have well defined kinetic energy which can be continuously tuned simply by scanning the photolysis laser frequency. Ultra-sensitive laser schemes are used to measure the energy level populations and angular momentum polarization of the gas phase products and grazing incidence Auger electron spectroscopy is used to detect the surface adsorbed reaction products. These experiments are performed in a new ultra-high vacuum chamber that was specifically designed to study the details of radical-surface chemistry. These experiments provide detailed information on the etching of semiconductor surfaces by halogen and hydrogen plasmas and by reactive ion beams.

The other type of experiments performed by our group utilize an electrostatic hexapole to produce beams of molecules in pure quantum states. These beams are used in conjunction with lasers to measure |j,m> state to |j',m'> state differential photofragmentation cross-sections which are directly related to the photofragmentation scattering matrix via integrals over the potential energy surface. Pure quantum state beams are also used to determine state-to-state differential cross-sections for bimolecular reactions. These very refined measurements are sufficiently quantitative to allow direct comparison with theoretical calculations in order to test the accuracy of the most current theories of elementary molecular reactions.