PhotoElectrons and Photoionization
Photoelectrons emitted from a sample of molecules irradiated by energetic photons carry with them a signature of the molecules left behind - both before, during, and even after after the photoionization event takes place. Examination of the angular distribution of photoelectrons, augmented by the use of intense, polarised and tunable light sources together with sophisticated detection schemes is being exploited to learn about the mutual interaction of electrons within a molecule. More conventional photoelectron spectroscopy, traditionally used to reveal electronic structure of the neutral molecule and quantum state of the resulting ion can now reveal stereochemistry - configuration and conformation - of sample of small biomolecules.
Fixed Molecule Angular Distributions
The random nature of a typical gas phase sample causes a significant loss of detail and potential information due to the implicit averaging over all molecular orientations found in the laboratory frame. The photoelectron angular distribution in the molecular frame is, in contrast, expected to be much richer in structure and to provide far more insight into the photoionization dynamics. We are using various experimental techniques to effectively fix the orientation of molecules in free space and have developed theoretical models to interpret the results.
PECD: PhotoElectron Circular Dichroism
Theory
We developed the first calculations, based upon electron scattering methods, to predict the chiral asymmetry observed in angle resolved photoemission with circularly polarized light. These calculations now have sufficient accuracy to predict absolute configuration and conformations of smaller natural product enantiomers. Current developments aim to examine vibrational effects in PECD.
Experiment
Both core level PECD (in the soft X-ray region) and valence PECD (VUV) have similarly been pioneered by the Nottingham group working in collaboration with other European researchers and utilising the latest synchrotron radiation sources of circularly polarized radiation. As experimental sensitivity is improved a number of extended projects are being planned and pursued.
Collaborations
- Laurent Nahon, Synchrotron Soleil, St. Aubin, France
- Uwe Hergenhahn, IPP Garching, Germany
- David Holland, Daresbury, UK.
- Mauro Stener, Universita di Trieste, Italy
- Katharine Reid, University of Nottingham, UK.