Chemical Applications of Velocity and Spatial Imaging

Ion imaging, first demonstrated just 25 years ago, is already having a major impact on the way we explore molecular change (the very essence of chemistry) in many gas phase systems. The technique has features in common with mass spectrometry (MS). Both start by removing an electron from the target species, generating ions, i.e. charged molecules or fragments, which are then 'sorted' by their mass. In traditional MS, the species of interest is characterised by its spectrum of ion yield versus mass. Electron removal in most ion imaging experiments is induced by a short pulse of laser light; the resulting ions are then accelerated towards a time and position sensitive detector. Heavier ions travel more slowly, so one can image ions of just one particular mass by ensuring that the detector is only 'on' at the appropriate time. The spatial pattern of ion impacts that builds up on the detector when the experiment is repeated many times is visually intuitive, and provides quantitative energetic information about the reaction(s) that yields the monitored product. However, the read out time of current ion imaging detectors is too slow to allow imaging of ions with different mass formed in the same laser shot, and many species are not readily amenable to ionisation in current ion imaging schemes. Imaging all products from a given reaction is therefore time consuming (at best) and, at worst, impossible.
We seek to solve both these limitations. Two of the team have already demonstrated new, much faster, time and position sensitive sensors capable of imaging multiple masses in a single shot experiment. This multimass imaging capability will be developed further and rolled-out for use and refinement across the team. We also propose new multiphoton ionization schemes as well as 'universal' ion formation methods based on use of shorter laser wavelengths or short duration pulses of energy selected electrons. The following over-arching scientific ambitions will proceed in parallel, and exploit the foregoing advances in ion imaging technology at the earliest possible opportunity:
(i) We will use the latest ion imaging methods to explore molecular change in the gas phase, focusing on key families of (photo)chemical reactions: addition, dissociation, cyclisation and ring opening reactions of organic molecules, and metal-ligand and metal-cluster interactions. These choices reflect the importance of such reactions in synthesis, catalysis, etc., their amenability to complementary high level theory, and our ability to explore the same reactions in solution (using a new ultrafast pump-probe laser spectroscopy facility). Determining the extent to which the mechanisms and energetics of reactions established through exquisitely detailed gas phase studies can inform our understanding of reactivity in the condensed phase is a current 'hot' issue in chemical science, which the team is ideally placed to address.
(ii) We will develop and exploit new multi-dimensional analytical methods with combined mass, structural and spatial resolution. Mass spectra usually show many peaks attributable to fragment ions, but the paths by which these are formed are often unclear. Imaging MS is proposed as a novel means of unravelling different routes to forming a given fragment ion; distinguishing and characterising such pathways can offer new insights into, for example, peptide structure. Yet more ambitious, we propose to combine multimass and spatial map imaging with existing laser desorption/ionisation methods to enable spatially resolved compositional analysis of surfaces and of samples on surfaces. Such a capability will offer new opportunities in diverse activities like tissue imaging (e.g. detection of metal ions within tissue specimens of relevance to understanding the failure of some metal-on-metal hip implants), forensic analysis (e.g. 'chemical' imaging of fingerprints, inks, dyes, pollens, etc) and parallel mass spectrometric sampling (e.g. of blood samples).

Five technical work packages (TWPs) underpinning four substantial scientific work packages (SWPs) are proposed. The TWPs centre on new and improved methods of (i) creating charged particles, (ii) detecting/imaging them with improved velocity, spatial and/or time resolution and (iii) integrated high-level modelling of the results of experiments (photodissociation or photoionization processes, bimolecular reactions, surface desorptions, etc) which depend on such measurements. Short term beneficiaries include the economy (e.g. companies developing and manufacturing improved fast charged particle imaging detectors/sensors, with several of whom consortium members already collaborate). Such devices already find many applications of benefit to society (e.g. monitoring bioluminescence, corona imaging, fluorescence lifetime imaging, time resolved imaging, high speed and/or low light level imaging, security detection systems, threat detection systems, missile warning systems, space science, etc), but the quest for new and improved performance is unending. On the longer term (but within the timescale of the PG), fast sensors of the type envisaged here should offer new opportunities in mass spectrometry (e.g. imaging mass spectrometry) - a pivotal research and analysis tool in broad areas of physical and life science - and more widely (e.g. in neutron science, electron microscopy, etc). Interest in new and improved neutron detectors has soared as a result of the current world shortage of 3He.
Apart from Instrument Development, the proposed SWP activities are envisaged to have longer term impact in several other areas of the EPSRC Portfolio: Healthcare Technologies (e.g. chemical analysis of bioarrays and tissue analysis, enabled by new high fidelity, mass selective, spatially resolved imaging methods), Energy (e.g. via improved understanding of catalytic sites and surfaces from gas phase, gas-surface and condensed phase studies), Manufacturing for the Future (e.g. improved understanding and application of condensed phase (photo)chemical reactivity). The latter SWP also impacts on the Dial-a-Molecule Grand Challenge in Chemistry - by providing a deeper understanding of chemical reactivity and the promise of greater control. Such science boosts the pool of knowledge available to synthetic chemists, the pharmaceutical industry, etc; the strength of associated synthetic chemistry and biochemistry groups at Bristol (which hosts the CDT in Chemical Synthesis) and at Oxford will help ensure efficient knowledge transfer.
Longer term benefits for society in general, the knowledge base and people will be delivered through the training of a new generation of research leaders skilled in quantitative, cutting edge experimental and theoretical physical chemistry/chemical physics, capable of identifying and solving problems of global importance, and by the development and application of novel instrumentation coupled with integrated high-level computational modelling. Recent destinations for group members include academia (e.g. new appointees at UC Irvine, Heriot Watt, Newcastle), post-doctoral research (e.g. UC Berkeley, VU Amsterdam, Berlin, Lausanne, Space Science Group and Diamond Synchrotron at RAL) and industry (e.g. Du Pont, Malvern Instruments, AWE, Shell International).