Mapping ultrafast energy flow in liquids

Chemistry is about breaking and making chemical bonds. On a microscopic level, breaking a chemical bond requires that a large quantity of energy is first localized in that particular bond. Similarly, making a chemical bond places lots of energy into a particular bond. Most chemical reactions take place with reactant molecules embedded in a sea of unreactive liquid (or solvent) molecules.  Common solvents, including water and organic liquids, play an important role in both shuffling energy to reacting molecules, and subsequently shuffling it away after reaction has occurred.  However, when chemists think about reactions in liquids, they tend to overlook the underlying energy shuffle that transports energy to and from the chemical reaction.  Instead, they focus on the equilibrium states that occur well before, and well after, a reaction occurs, which are well described by a theoretical paradigm based on linear response theory and the fluctuation-dissipation theorem.

In a paper featured on the cover of Nature Chemistry, we used state-of-the-art computational models run on Bristol supercomputers to construct a ‘map’ of how energy flows at times as short as one millionth of a millionth of a second after a chemical reaction. This  level of detail allowed us to resolve the energy shuffle associated with individual bond making and breaking in liquids, and reveals clear shortcomings in the physical models commonly used to describe the energy shuffle occurring alongside chemical reactions.  The new insight afforded by such ‘energy flow maps’ has the scope to help chemists working in areas as diverse as biochemistry, pharmaceutical chemistry, polymer chemistry, and nanoscience.

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