IMAGINGELECTRONS · Photoelectron Imaging and Spectroscopy of biomolecules using VUV light

Photoelectron Imaging and Spectroscopy of biomolecules using VUV light

The principal objective of the proposal was to develop a photoelectron imaging apparatus and to investigate the photoelectron spectroscopy of molecules of biological interest using vacuum ultraviolet light sources both in the laboratory and at synchrotron sources. Photoelectron imaging involves the ionisation of an atom or molecule by interaction with light in the VUV range. The photoelectron thus produced is then projected onto a position sensitive detector and the image formed by the projection of thousands of such electrons can then analysed in order to extract the kinetic energy and angular distribution of the photoelectrons. This information can then be used to glean detailed insights both into the electronic structure of the target and the dynamics of photoionisation. During this project the fellow (Patrick O'Keeffe) together with the host group - Lorenzo Avaldi, Paola Bolognesi, Yevgehniy Ovcharenko (visiting scientist) and Luka Pravica (visiting scientist) - as well as the staff of the gas phase beamline and the detectors laboratory at the Italian synchrotron source, Elettra, has designed and built a photoelectron imaging apparatus as well as put together the necessary image analysis procedures for extracting the above information (P. O'Keeffe et al., 'A photoelectron velocity map imaging analyser for experiments combining synchrotron and laser radiation', Rev. Sci. Instrum. 82 (2011) 033109). In particular, this instrument has been used in experiments combining visible laser light with the VUV synchrotron radiation. This combination allows the preparation of the atom or molecule to be ionised in a very well controlled state thus permitting us to study the photoionisation process in a more in depth fashion with respect to single photon ionisation. This method has been used to investigate the photoionisation of rare gas atoms and small molecules. Methods to combine this detailed state-of-the-art photoionisation detection method with molecules of biological interest have been examined and resulted in the building of a seeded supersonic jet source coupled to the photoelectron instrument. Increasingly complex systems are being considered with the apparatus being coupled to a nanoparticle cluster source and in the future a helium droplet source. In the final year of the project, the imaging apparatus was adapted for use with FERMI the Italian free electron laser in the VUV region under development at Trieste, Italy. A second part of the project has concentrated on the investigation of the effects of soft X-ray and VUV light on organic molecules of biological interest. The methods used included photoelectron spectroscopy and coincident ion techniques to examine fragmentation process following photon absorption. The project has resulted in quite a large quantity of published material with eight internationally refereed ISI journal articles, eight international refereed non-ISI journal articles and a chapter in a book on radiation damage of biological molecules. Three of these articles have been selected for publication in the Research Highlights book of the Italian synchrotron light source where much of this work was performed. Finally, the research of the project has resulted in six invited talks by the research fellow including three at international conferences / meetings.

Data: CORDIS, © European Union