Page 16 - PERIODIC 2017
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Mo                lecular Movies

              Researchers Michael Burt, Alexander Gentleman and Jason Lee
              explain how the ultra-fast PImMs camera enables scientists to watch
              chemistry as it happens.

              Our world is composed of molecules that constantly   valuable information about how the energy deposited into
              interact, and this interplay controls everything from the   a molecule is redistributed over time. This redistribution
              behaviour of the atmosphere to the biology in every   can cause the molecule to change shape, become
              cell. The Nobel-Prize-winning field of reaction dynamics   vibrationally and electronically excited, or to break up
              investigates chemical interactions at the atomic level with   into smaller fragments. Observing these processes sheds
              the aim of explaining, and eventually controlling, how   light on the underlying chemistry and directly probes the
              chemical reactions take place. Over the past few years,   “energy landscape” of the molecule, which defines all of
              the research groups of Mark Brouard, Stuart Mackenzie,   the molecular forces and behaviour, and in particular their
              and Claire Vallance (University of Oxford) have been   likelihood to undergo particular reactions. The specialised
              working with the groups of Mike Ashfold, Jeremy Harvey,   electronics in the PImMS sensor allow it to operate at
              and Andrew Orr-Ewing (University of Bristol) as part of an   80 million frames per second, fast enough to separate
              EPSRC Programme Grant that explores the dynamics of   chemical fragments based on their mass, and to watch
              new chemical systems and develops novel experiments   chemistry as it occurs.
              that push the boundaries of this field.
                                                               In combination with ultra-fast laser pulses, the PImMS
              One promising research direction involves the    sensor can be used to investigate molecular structures.
              development of a new sensor capable of watching   Intense radiation can ionise multiple electrons from
              chemistry in action. Scientists from Oxford Chemistry,   a molecule, removing the bonds holding the nuclei
              Oxford Physics and the Rutherford Appleton Laboratory   together. Repulsion between the positively charged nuclei
              have combined their expertise to create the Pixel Imaging   causes the molecular ion to explode into fragments with
              Mass Spectrometry (PImMS) sensor, which provides   trajectories that are governed by Coulomb’s law. If the

                The torsional angle   between two halogen-substituted benzene rings monitored by recording their Coulomb
                explosion fragment images using the PImMS sensor. Fragment images were acquired at delays up to four picoseconds
                after the initiation of the torsional motion by a laser pulse. In this example, the PImMS image illustrates the fluorine
                fragment momenta relative to a fixed axis for the bromine fragments. The angle between the two ion trajectories
                oscillates as a function of time, creating a molecular ‘movie’ of the dynamics.

              Periodic       The Magazine of the Department of Chemistry
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