Aaron Wech, Ph.D.


Education: Bachelor of Science in mathematics and physics (May 2005)

Doctor of Philosophy in geophysics from the University of Washington

McNair Prjoect: Electron Capture from Atomic + Molecular H by O8+ at Low and Intermediate Impact Energies (2003)

Mentor: C. Lewis Cocke, Ph.D.

This experiment measured single electron capture from atomic and molecular hydrogen targets by O8+ ions at projectile velocities ranging from 0.5 to 0.95 a.u. The energy gain as well as the projectile transverse momentum gain was recorded through the use of cold target recoil-ion momentum spectroscopy. For this capture reaction, the reaction window was found to increase as the projectile energy increased. The angular distributions for the atomic hydrogen interactions center at the half Coulomb angle over the lower velocity range, but higher scattering angles for the lower energy gains were found at higher velocities (vp = 0.95 a.u.). These higher scattering angles for lower energy gains were also prevalent over the entire projectile velocity range studied in the molecular hydrogen interaction. In the atomic hydrogen collisions at all velocities, the n = 5 states were dominantly populated, as predicted by theory (Teck Lee), though the n = 6 state was also heavily populated, contrary to theory. Also, differing from theoretical predictions, the presence of both n = 7 and n = 4 populations were measured at all velocities with the relative cross section of each increasing with increasing velocities due to the reaction window increase. The close-coupling calculations for the over- the-barrier model are able to accurately describe the dominant channel of capture, but this theory shows little evidence of its ability to accurately describe the relative cross sections of the final captured states.