New Horizons in Chemical and Photochemical Dynamics

Lead Research Organisation: University of Bristol
Department Name: Chemistry

Abstract

Chemical change, whether caused by collisions between reactive atoms, radicals and molecules, or by absorption of light (photochemistry), is of fundamental importance in all branches of Chemistry. For example, synthesis of complicated organic molecules, such as those naturally occurring in plant and animal life, or needed to construct functional modern materials, requires an in-depth understanding of reaction mechanisms to design synthetic pathways. Ideas from physical chemistry based on thermodynamics and reaction rate theory underpin our ability to predict directions of chemical change and how quickly such change will occur. The fields of chemical reaction and photodissociation have sought to place such theories on a quantitative foundation built on deep understanding of the quantum mechanics of breakage and formation of chemical bonds. Potential energy surfaces (PESs) (based on the Born-Oppenheimer separation of the fast motion of light electrons from the slower motion of heavier atomic nuclei) are an essential concept because they provide a map of the energy landscape(s) over which chemical change occurs. Minima and barriers on the PESs correspond, respectively, to stable conformations of the atoms and short-lived transition states. Photodissociation involves dynamics on PESs lying higher in energy than the lowest, ground state, with the extra energy needed to reach these excited states provided by absorption of light. A powerful driver for advances in understanding of the dynamics of photochemical and reactive processes has been a close interaction between experimental and theoretical studies - arguably, the field has done much to stimulate the development of theoretical methods to calculate PE landscapes and describe the molecular dynamics on these surfaces. Such methods (subject to simplifying approximations) are now finding widespread use in molecular modelling of, for example, drug design, enzyme catalysis, and many other fields. The historical development of experimental and theoretical methods has relied on complementary studies of systems with only a small number of atoms (e.g. photodissociation of diatomic and triatomic molecules; reaction of atoms with diatomic molecules) so that accurate PESs can be computed and precise, quantum-mechanical (QM) scattering calculations carried out. Such experiments were mostly conducted in the gas phase, in the low-temperature and rarefied environment of a molecular beam, so that complicating factors of solvation, or interaction between molecules can be ignored. Considerable success with such systems has, for example, revealed the importance of exotic QM effects in chemistry such as tunnelling through reaction barriers, scattering resonances, non-adiabatic coupling between PESs, and interference between different pathways to the same products. For a photochemical or reactive system with 3 atoms, only 3 coordinates are required to describe all the possible arrangements of the atoms and the associated PEs can thus be computed for representative configurations spanning the entire PE landscape. We now seek a multi-pronged approach to extend such studies to more complicated systems, with the intention of learning about PE landscapes for larger molecules (for N atoms, 3N-6 coordinates are needed to describe the associated PE hypersurface), the effects of jumps between PE surfaces, and to examine how the energy landscapes and chemical dynamics are changed in the presence of solvent. In so doing, we will bring the fields of reaction and photodissociation dynamics closer to the types of chemical reactions used in synthesis by organic, inorganic and biological chemists. Our strategy involves development of new experiments and theoretical methods. The substantial challenges necessitate a consortium-based approach, in which complementary expertise in two Universities is brought together to address selected problems from which we can learn much about chemical change.

Publications

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Abou-Chahine F (2013) Photoisomerization and photoinduced reactions in liquid CCl4 and CHCl3. in The journal of physical chemistry. A

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Allum F (2018) Coulomb explosion imaging of CHI and CHClI photodissociation dynamics. in The Journal of chemical physics

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Aoiz FJ (2015) A new perspective: imaging the stereochemistry of molecular collisions. in Physical chemistry chemical physics : PCCP

 
Description This EPSRC Programme Grant involving 10 research groups from the Universities of Bristol and Oxford, is making significant advances in the fundamental study of mechanisms of chemical and photochemical reactions. The use of new technology to study such chemical processes is also leading to innovations in broader areas such as analytical science. Full details of the project are given at the website http://dynamics.chem.ox.ac.uk/ and a few key outcomes to date are summarized here. (1) Advances in mass spectrometry using novel imaging detectors that can provide both spatial and velocity information. (2) Breakthroughs in the study of chemical and photochemical processes occuring in solution in liquids using femtosecond laser based transient absoprtion methods and new theoretical methods for accurate simulation of reactions in liquids. (3) Use of velocity map imaging (and related) methods to observe collisional scattering and photodissociation mechanisms with quantum-state resolution, and to explore non-adiabatic dynamics at conical intersections between electronic states. (4) Advances in fundamental theory of chemical reactions, and of the theoretical treatment of bulk liquids. (5) Develpment and application of new methods to study collisions at ultra-low temperatures.



The consortium has published more than 150 papers in international journals over the course of the grant. A representative selection of these papers is given here.
Exploitation Route Advances in spatial and velocity map imaging led to the award of a Programme grant to the Bristol and Oxford groups to develop further these techniques and their applications (EP/L005913/1).

Collaborations with SMEs Photek Ltd and SAI Ltd, as well as the PImMS consortium involving the Rutherford Appleton Laboratory and University of Oxford are advancing technical developments and applications of imaging techniques, including new methods for imaging mass spectrometry.

Computational developments, for example in accurate simulation of reactions in solution, are being incorporated into major software packages for simulation of biomolecule dynamics such as CHARMM.
Sectors Chemicals,Creative Economy,Education,Energy,Environment,Healthcare,Pharmaceuticals and Medical Biotechnology,Other

URL http://dynamics.chem.ox.ac.uk/
 
Description Developments in imaging mass spectrometry and in imaging methods are transferring to mass spectrometry manufacturers (e.g. Scientific Analysis Instruments Ltd)and manufacturers of scientific instrumentation for imaging (e.g. Photek Ltd, Photonis). The development of the Danceroom Spectroscopy project is having a substantial cultural and educational impact: see http://danceroom-spec.com/ for a list of activities.
First Year Of Impact 2009
Sector Creative Economy,Education,Manufacturing, including Industrial Biotechology
Impact Types Cultural,Economic

 
Description EPSRC Programme Grant
Amount £4,663,077 (GBP)
Funding ID EP/L005913/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 01/2014 
End 09/2019
 
Description ERC Advanced Grant
Amount € 2,666,684 (EUR)
Funding ID 290966 
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 02/2012 
End 01/2017