In order to fully describe a chemical reaction from first principles theoretically a detailed calculation, or picture, of the reactive potential energy surface must be carried out. However, given the many degrees-of-freedom to be considered for the reactants, products and the extremely short-lived transition state, (i.e. all of the internal structure and dynamics) these calculations can become unwieldy very quickly. Because of this experimental measurements are invaluable as an aid to theory in determining what level of complexity is required to generate meaningful theoretical results.

This project will investigate these potential energy surfaces and in particular the transition state, or point, between the reactants and products of a chemical reaction using our unique and world-leading velocity-map imaging spectrometer, through the detection of photoelectrons at very high electron energy resolution. Through combining the use of weakly bound negatively charge clusters and laser photodetachment of these clusters information will be gleaned on the potential energy surfaces and the transition states. One such clusters or reaction to be studied is H₃O- which can exist as either a OH^-•• H₂or H₂O•• H^-cluster and can be used to probe the H₂O + H↔ OH + H₂reaction. Isomerisation reactions such as the H₂CC (vinylidene)↔ HCCH (acetylene) reaction can also be studied via this technique.

To cater for students who wish to have some additional scientific instrument construction as part of their project the candidate(s) can choose one or more of instrument-based components listed below. These projects are:

1) Construction of a new anion source and pulsed gas jet. These two devices are an integral part of the fast ion beam velocity-map imaging spectrometer. The new designs will attempt to overcome some inherent problems with the older design currently in use and it is expected that they will allow for the delivery of a more stable and controlled anion beam. The anion source is based upon an electrostatic Brink-type electron ionization source (Amirav et al, Rev. Sci. Instrum.,73(8), 2002, pg 2872) while the pulsed jet design will attempt to produce cooled short pulsed (10μsec) gas beams and is based upon the design of Even et al, Rev. Sci. Instrum.,112(18), 2000, pg 8068.

2) Construction of an ion beam detector to enable measurement of the absolute number density, per shot, of the anion beam. This will require: a) construction and installation of a set of pulsed ion-beam electrostatic deflectors and the installation of a high count rate and high gain charged particle detector, b) computer interfacing a waveform analyser to read the signal from each ion beam packet at 50 Hz and c) in addition to the ion beam detection, computer interfacing a waveform analyser to read the signal/intensity from each laser beam pulse.

3) Construction of a new Velocity-Map Imaging electrostatic lens, the design of which will improve on our current design both in terms of energy resolution and the lowest possible electron kinetic energy detectable, by 8-10 times. This construction will require the student to finalise some electrostatic modelling ofthe imaging lens, then leas with both academic and technical staff on its design and then implementation and characterisation.