Research Guides

Work in my group is focussed in two main research areas: 1) molecular reaction dynamics and 2) imaging mass spectrometry.

1. Molecular Reaction Dynamics:

Our work in reaction dynamics concerns studying the dynamics of simple unimolecular and bimolecular chemical reactions in the gas phase. To do this, a technique known as velocity-map ion imaging (VMI) is used, which enables us to directly image the velocities of the nascent products of a reaction. This is usually coupled with resonantly enhanced multiphoton ionization (REMPI), which facilitates quantum-state resolved detection of products. These experiments can also employ the use of external magnetic or electric fields in order to align or orient reactants, or to select reactants in a specific quantum state¹. The measured velocity distributions give a very detailed insight into the nuclear motion during the reaction, as well as the electronic state(s) involved. The results are supported by high level ab initio quantum and classical scattering calculations. Recent work in this areas include studies into the inelastic collisions of NO with rare gases, in which key aspects of the scattering dynamics have been shown to arise due to quantum interference effects between scattering at either end of near homonuclear molecule^2,3.

2. Imaging Mass Spectrometry

Our work in imaging mass spectrometry involves the development of experiments in which an ion’s velocity or spatial information is provided simultaneously with each peak in a time-of- flight mass spectrum. This work is facilitated by the novel PImMS sensor⁴, which has been developed in collaboration with Professor Claire Vallance, and colleagues in Oxford Physics and the Rutherford Appleton Laboratory. This technique has been applied to spatial surface imaging^5,6 and covariance imaging^7-9. The former allows for a spatially resolved mass spectrum to be taken of a given surface. To do this, the sample is ablated with a defocussed laser beam, releasing ions from the surface. These ions are accelerated towards the detector using electric fields which preserve the original ion spatial distribution. This has potential to be a useful analytical tool in chemical analysis of surfaces, tissue samples, and parallel, high throughput sample analysis using mass spectrometry.

Covariance imaging uses a statistical data analysis technique to extract correlations between the velocities of different ions. The combination of covariance imaging with Coulomb explosions induced by ultrafast lasers has allowed for direct imaging of the structure of complex polyatomic molecules on a femtosecond timescale⁷. Coulomb explosion imaging has also been used to investigate the nuclear motion in molecular photodissociation⁸ and in vibrationally excited systems⁹ in real time.

1. A new perspective: imaging the stereochemistry of molecular collisions, F.J. Aoiz, M. Brouard, S.D.S. Gordon, B. Nichols, S. Stolte, and V. Walpole, Physical Chemistry Chemical Physics, 17, 30210 (2015)
2. Steric effects and quantum interference in the inelastic scattering of NO(X) + Ar, B. Nichols, H. Chadwick, S.D.S. Gordon, C.J. Eyles, B. Hornung, M. Brouard, M.H. Alexander, F.J. Aoiz, A. Gijsbertsen, and S. Stolte, Chemical Science, 6, 2202 (2015)
3. The origin of collision-induced molecular orientation,  M. Brouard, B. Hornung, and F.J. Aoiz

   Physical Review Letters, 111, 183202 (2013)

4. PImMS, a fast event-triggered monolithic pixel detector with storage of multiple timestamps, J.J. John, M. Brouard, A. Clark, J. Crooks, E. Halford, L. Hill, J.W.L. Lee, A. Nomerotski, R. Pisarczyk, I. Sedgwick, C.S. Slater, R. Turchetta, C. Vallance, E. Wilman, B. Winter and W.H. Yuen,  Journal of Instrumentation, 7, C08001 (2012)
5. Modifications to a commercially available linear mass spectrometer for mass-resolved microscopy with the pixel imaging mass spectrometry (PImMS) camera,  E. Halford, B. Winter, M.D. Mills, S.P. Thompson, V. Parr, J.J. John, A. Nomerotski, C. Vallance, R. Turchetta, and M. Brouard, Rapid Communications in Mass Spectrometry, 28, 1649 (2014)
6. Mass-resolved ion microscope imaging over expanded mass ranges using double-field post-extraction differential acceleration. International Journal of Mass Spectrometry. A. Guo, M.B. Burt, and M. Brouard, in press (2017)
7. Covariance imaging experiments using a pixel-imaging mass-spectrometry camera,  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, Physical Review A, 89, 011401(R) (2014)
8. Coulomb-explosion imaging of concurrent CH₂BrI photodissociation dynamics, M.B. Burt et al.  Physical Review A, 96, 043415 (2017)
9. Dynamic Stark control of torsional motion by a pair of laser pulses, L. Christensen, J.H. Nielsen, C.B. Brandt, C.B. Madsen, L.B. Madsen, C.S. Slater, A. Lauer, M Brouard, M.P. Johansson, B. Shepperson, and H. Stapelfeldt, Physical Review Letters, 113, 073005 (2014)