Research Guides

Professor C. Vallance

Our group works in the general areas of chemical reaction dynamics and new spectroscopic methods and applications.  Our work ranges from fundamental studies of photon and electron-induced chemistry to the development of new types of chemical sensor and applications of spectroscopy in medicine.  Some recent research projects are outlined in the following.

Photoinduced and electron-induced chemical reactions

Chemical reactions initiated by light or by collisions with electrons play an important role in atmospheric chemistry, astrochemistry, synthetic chemistry, and biology.  Understanding the mechanisms of these reactions in detail offers new insight into a range of vital physical and chemical processes, ranging from the breaking of a single chemical bond all the way through to complex multistep processes occurring in biological systems.

We study photoinduced and electron-induced chemistry in the gas phase, using velocity-map imaging to record scattering distributions of reaction products.  These distributions can be analysed in order to unpick details of the reaction mechanism.

Examples of photochemical systems we have studied recently include photolysis of neutral and ionic ethyl bromide and ethyl iodide, which play a role in the marine boundary layer of the Earth's atmosphere, and photolysis of N,N-dimethylformamide, a model for peptide bond fragmentation.  A sample data set for the latter system is shown below. We plan to extend the latter measurements to a number of related molecules in order to understand the role of different side chains on peptide bond fragmentation.


In addition to studying photoinduced chemical processes, we also study processes initiated by collision of a molecule with an electron.  These include electron ionization and fragmentation, all of which are interesting both from a fundamental point of view and for improving our understanding of electron-induced processes in astrochemistry, plasma chemistry, and biology.


Ultrafast detectors for time-of-flight imaging

We are part of the PImMS (Pixel Imaging Mass Spectrometry) consortium, a group of researchers working to develop ultrafast imaging sensors suitable for applications in time-of-flight mass spectrometry.  The sensors allow velocity-map or spatial-map images to be acquired for each mass peak in a time-of-flight mass spectrum, opening up a range of new applications in mass spectrometry, state-of-the-art chemical dynamics studies, neutron detection, and other fields of science.  More information on the PImMS detectors is available here.


Spectroscopic and mass spectrometric measurements to aid surgical decision making

We are working with two clinical groups at the John Radcliffe hospital on applications of various types of spectroscopy to clinical samples.  In the first, we are working with clinicians Regent Lee, Gianluigi de Maria, and Prof. Keith Channon to evaluate whether reflectance spectra of thrombus removed from coronary arteries following STEMI (heart attack) can be used to classify patients into high and low risk groups, and therefore to guide clinical decisions during the acute treatment phase.  In the second, we are working with neurosurgeon Mr Puneet Plaha and neuropathologist Prof. Olaf Ansorge to investigate the use of Raman and fluorescence spectroscopy and imaging mass spectrometry for the genetic characterisation of brain tumours and delineation of tumour borders.


Optical microcavities for chemical sensing

Over the past few years we have been working with Prof. Jason Smith's group in Oxford Materials to develop miniature optical cavities for applications in solution-phase chemical sensing and nanoparticle characterisation.  Microcavities are only a few wavelengths in length, giving them interesting optical properties, and contain tiny quantities of liquid, often only a few tens of femtolitres.   As with any optical cavity, light forms standing waves known as cavity modes at well defined frequencies within the cavities.  By tracking changes in the frequencies and intensities of individual cavity modes when a sample is introduced into the cavity, we can detect and characterise single nanoparticles, and perform chemical sensing down to the few-molecule level.  Most of this work has now been transferred into our new spin-out company, Oxford HighQ.

  • S.-M. Wu, D. C. Radenovic, W. J. van der Zande, G. C. Groenenboom, D. H. Parker, C. Vallance, and R. N. Zare, ‘Control and imaging of O(1D2) precession’, Nature Chemistry, 3 28 (2011).
  • C. Vallance, 'Generation, characterisation, and applications of atomic and molecular alignment and orientation', Phys. Chem. Chem. Phys., 13 14427 (2011).
  • A. T. Clark, J. P. Crooks, I. Sedgwick, R. Turchetta, J. W. L. Lee, J. J. John, E. S. Wilman, L. Hill, E. Halford, C. S. Slater, B. Winter, W. H. Yuen, S. H. Gardiner, M. L. Lipciuc, M. Brouard, A. Nomerotski, and C. Vallance, 'Multi-mass velocity-map imaging with the pixel imaging mass spectrometry (PImMS) sensor: an ultra-fast event-triggered camera for particle imaging', J. Phys. Chem. A, 116(45), 10897 (2012).
  • C. Vallance, M. Brouard, A. Lauer, C. Slater, E. Halford, B. Winter, S. J. King, J. W. L. Lee, D. Pooley, I. Sedgwick. R. Turchetta, A. Nomerotski, J. J. John, and L. Hill, 'Fast sensors for time-of-flight imaging applications', Phys. Chem. Chem. Phys., 16, 383-395 (2013).
  • J. N. Bull, J. W. L. Lee, S. H. Gardiner, and C. Vallance, ' An introduction to velocity-map imaging mass spectrometry (VMImMS)', Eur. J. Mass Spectrom., 20(2), 117-129 (2014).
  • S. H. Gardiner, T. N. V. Karsili, M. L. Lipciuc, E. Wilman, M. N. R. Ashfold, and C. Vallance, 'Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study', Phys. Chem. Chem. Phys., 16(5), 2167-78 (2014).
  • C. S. Slater, S. Blake, M. Brouard, A. Lauer, C. Vallance. J. J. John, R. Turchetta, A. Nomerotski, L. Christensen, J. H. Nielsen, M. P. Johansson, and H. Stapelfeldt, 'Covariance imaging experiments using the Pixel Imaging Mass Spectrometry camera', Phys. Rev. A., 89, 011401(R), (2014).
  • J. N. Bull, J. W. L. Lee, and C. Vallance, 'Absolute electron impact total ionization cross-sections: molecular analogues of DNA and RNA nucleobase and sugar constitutents', Phys. Chem. Chem. Phys., 16, 10743-52 (2014).
  • C. Vallance, A. P. Trichet, D. James, P. R. Dolan, and J. M. Smith, 'Open access microcavities for chemical sensing', Nanotechnology, 27, 274003 (2016) .
  • A. A. P. Trichet, P. R. Dolan, D. James, G. M. Hughes, C. Vallance, and J. M. Smith, 'Nanoparticle trapping and characterisation using open macrocavities', Nano Lett., 16(10), 6172-6177 (2016).
  • M. L. Lipciuc, S. H. Gardiner, J. W. L. Lee, T. N. V. Karsili, M. N. R. Ashfold, and C. Vallance, 'Photofragmentation dynamics of N,N-dimethylformamide following excitation at 193 nm', J. Chem. Phys., 147(1), 013941 (2017).



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