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EPSRC Reference: EP/G004943/1
Title: High resolution exploration of f-wave emission in ro-vibrational autoionisation in H2
Principal Investigator: Siggel-King, Dr MRF
Other Investigators:
King, Professor GC
Researcher Co-Investigators:
Project Partners:
Department: Photon Science
Organisation: STFC Laboratories (Grouped)
Scheme: Overseas Travel Grants (OTGS)
Starts: 10 April 2008 Ends: 09 July 2008 Value (£): 11,226
EPSRC Research Topic Classifications:
Light-Matter Interactions
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:  
Summary on Grant Application Form
Molecular hydrogen is the simplest and most abundant neutral molecule in the Universe. Due to its relative simplicity it is the natural starting point for both experimental and theoretical studies. It is also gaining technological importance through its use in fuel cells for the environmentally-friendly production of energy. A fundamental process involving molecular hydrogen is photoionisation by ultra violet light where a photon ejects an electron from the molecule. However, despite the simplicity of the molecule its photoionisation spectrum is not simple and smooth, as would be expected if the photon ionised the molecule in a direct manner. Instead it is dominated by a wealth of sharp structure which arises because it is much more likely for photoionisation to occur in a two-step process. Here a high-lying, neutral state of H2 is first excited by absorption of a photon. This state then decays to the molecular ion H2+ with the emission of a photoelectron in a process called autoionisation. Apart from being the dominant process, autoionisation is important because it also involves interactions between electronic motion and the molecular motions of rotation and vibration, which do not occur in direct photoionisation. The excitation and decay paths involved in this two-step process can be investigated by observing the energies and yields of the ejected photoelectrons. Furthermore, by measuring the angular behaviour of the emitted photoelectron it is possible to investigate the angular momentum exchanged between the photoelectron and the molecular ion. In practice this picture becomes more complicated because more than one rotational level of the hydrogen molecule is populated at room temperature. The photoionisation spectra are then considerably more complex, and more importantly, it makes it much more difficult to connect experiment with theory. Previous experiments have generally been a sum over several rotational levels of the ground vibrational state of H2. This lack of rotationally-selected experimental data remains a road block to the theoretical development of this fundamental system. We have developed experimental techniques to remove this road block where we put more than 99% of the target H2 molecules into a single rotational level. We have designed and built an electron spectrometer that allows us to identify individual rotational levels of the final ionic state and to measure the angular behaviour of the photoelectrons. We have also been granted access to an ultra violet light source (the GasPhase beamline at Elettra, Italy) with the necessary spectral resolution to isolate individual rotational levels of the intermediate neutral states. Brought together this enables a comprehensive study of photoionisation in a molecule for well defined rotational states in (1) the initial target state, (2) the intermediate state and (3) the final ion state. A final capability is that we can substitute H2 by the isotope D2. This slightly shifts the molecular energy levels and can reveal transitions that are otherwise hidden while the change in inter-nuclear separation modifies the dynamics of the photoionisation process. The proposed experiments would thus provide a complete and clear picture of photoionisation in this fundamental molecular system.
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