The long-term goal of this project is the provision of accurate (benchmark) results for the near-threshold electronic excitation of complex molecules, including molecules of biological significance.

This region is a challenge experimentally as measurements typically require stable, high-resolution electron monochromators and analysers, as well as a sound strategy for establishing the absolute magnitude of the scattering cross sections. The most commonly used approach has been to measure the flux of inelastically scattered electrons, relative to that for the elastic scattering intensity at the same incident energy and scattering angle. The main experimental issue that has to be resolved is usually the determination of the transmission of the energy analysing device (e.g., a hemispherical analyser) as a function of the scattered electron energy. In many cases this proves to be the largest source of experimental error.

To overcome this we have constructed at the ANU a new time-of-flight energy analyser as the dispersive element for the scattered electron analysis. The significant advantages of the ToF technique are that it is multi-channel, with the concomitant efficiency gains. Also, in the absence of external electric and magnetic fields in the flight region, the transmission between target and detector is independent of the energy of the scattered electrons. This potentially removes a major source of uncertainty for near-threshold inelastic scattering measurements.

This project will involve extending the application of the ToF spectrometer to the study of molecular systems. Such systems have a considerably more complex electronic structure and the experimental data will normally consist of a series of overlapping peaks in the measured timing (energy loss) spectrum which need to be‘unfolded' to yield the intensities for each excited level. The molecules that we initially plan to study are N₂, H₂and H₂O. The student involved with this project will develop skills in charged particle transport, vacuum systems, electronics and gas handling as well as computer based experimental control and data acquisition. Also, the analysis of experimental data and the further development of existing analytical tools will be required, as will the preparation of the research for publication and presentation at conferences.