Hitchcock Research Group: grad studies

GRADUATE STUDENTS NEEDED for

Ionic Fragmentation of inner-shell excited species GOAL: To use an existing time-of-flight mass spectrometer equiped with multi-coincidence detection to investigate the photo-ionization dynamics (time-evolution) of inner-shell excited molecules. The time-evolution of an inner-shell excited state has a built-in clock (the characteristic time for filling the core-hole) such that the kinematics of a multi-ion fragmentation process (i.e. the energy and angular distribution of the ions) provide detailed information about the bond-breaking steps. We derive fragmentation kinematics from detailed analysis of peak shapes in ion-ion multi-coincidence maps (analagous to 2d-nmr). Scientifically, we are interested in better understanding site- and state-selectivity in the bond breaking processes of medium sized molecules, as well as quantifying the strengths of different processes, in order to evaluate the potential utility of selective energy X-ray photochemistry. Such information is of practical use for understanding energy-assisted chemical vapor deposition, for example.REFERENCES: Various recent papers in this area, including a review, can be found in the core state photofragmentation publication list.

NATURE of STUDIES: You will use our gas phase time-of-flight apparatus on several beamlines at the Synchrotron Radiation Center of the University of Wisconsin-Madison to investigate yields and line-shapes of ionic fragmentation processes. Currently the grasshopper line gives access to 100-250 eV, and the double crystal line gives acsess to 1800-4000 eV. A spherical grating line will be available fall-99 giving access to 280-600 eV and thus access to the C 1s, N 1s and O 1s core levels. You will also take part in an upgrade of the time-of-flight apparatus, to develop a higher efficiency device which will be used for both gas phase and surface ionic desorption studies.

SKILLS ACQUIRED: Working in a group environment (synchrotron radiation); knowledge of core excitation electronic spectroscopy (NEXAFS) and photo-fragmentation dynamics theories; knowledge of all aspects of instrumentation (vacuum, mechanical, electronics, gas handling etc); programming.

YOUR THESIS: would report your results and the extraction and interpretation of photoionization kinematics information on a number of small and mid-size molecules, in order to use chemical systematics to assist interpretation. It would also describe your contributions to improvements to the instrumentation, data treatment and computational techniques.

SPECIAL BENEFITS: expertise with synchrotron radiation instrumentation (the 2.9 GeV Canadian Light Source will be coming on line in 2003 and will provide many employment opportunities