Vibrational and Electronic Excitation of Molecules by Positron and Electron Impact
- Chief Supervisors
- Assoc. Prof. M.J. Brunger (Flinders University)
- Prof. S.J. Buckman (Australian National University)
- Supervisors
- Dr. J. Sullivan, (Australian National University)
- Dr. L. Campbell (Flinders University)
- Centre Nodes
- Flinders University
- Australian National University
- Collaborators
- University of California Davis
- Lawrence Berkeley Laboratory
For many positron- and electron-driven processes, inelastic scattering, where the projectile positron or electron loses energy in exciting internal degrees of freedom of the molecular target, is an extremely important process. Many of these processes lead to the emission of radiation, across the spectrum from the IR to the VUV, and to the production of long lived (metastable) excited states with significant amounts of internal energy.
This project will focus on the measurement of accurate, absolute integral cross sections for the excitation of a range of atoms and molecules by both positron and electron impact. It will use the Positron Beamline Facility at the ANU, which has the unique capacity to provide direct measurements of integral cross sections for both positrons and electrons, together with complementary, conventional electron spectrometers at Flinders University, to provide a broad range of absolute cross section data. The atoms and molecules to be studied will range from the relatively simple to the rather complex, and the research program will be focussed on providing both benchmark measurements for the evaluation and development of theoretical techniques, and measurements that are of relevance in technology and/or the environment.
Another feature of the work will be a detailed comparison/contrast of the measurements for both electrons and positrons. In some cases, the lack of the exchange interaction with positron impact will greatly simplify the excited state spectroscopy, as it can effectively remove any probability of exciting a whole class of states which require electron exchange (or spin-orbit interaction, which is also weak for positrons). In these cases positron spectroscopy could prove to be an excellent complement to the more conventional electron spectroscopy. Positron interactions can also lead to the formation of positronium, where an electron is removed from the atom or molecule and an electron-positron pair temporarily formed. This is a major energy loss channel which ultimately leads to ionization and is an interesting process for study.
Theoretical support for the experimental work will be provided by the teams at the University of California Davis, and The Lawrence Berkeley Laboratory, through the application of their Kohn variational technique.
Student(s) undertaking this project will develop skills in high vacuum technology, charged particle optics and beams, positron and electron detectors, data analysis, computer interfacing to experimental apparatus and atomic and molecular spectroscopy. The student could be located at either Flinders University in Adelaide or the Australian National University in Canberra, although some travel between the two will be necessary.
