Dynamics, Control and Energy Transfer at Terahertz Frequencies.

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Chemical and biological reactions are governed by the coupling of ultrafast chemical events to dynamics on much slower timescales. These ultrafast chemical events often occur at THz frequencies and there is a range of indirect experimental and theoretical evidence to suggest that the coupling of vibrational motion at these frequencies governs the dynamics of a range of reactions across chemistry and biology. In this proposal, enabled by recent technological developments, I will develop a THz multidimensional spectrometer that will be able to measure directly the coupling between these modes on an ultrafast timescale. This will enable me to measure energy transfer between THz frequency modes and the timescales involved therein. Once demonstrated this will be a new, powerful analytical technique with many possible applications. Initial measurements will be performed on two very different material types, the first being energetic materials, and the second, materials that show a dramatic structural change upon illumination by light (a photo-induced phase transition or PIPT). In both materials there is strong indirect experimental and theoretical evidence that the coupling between THz frequency vibrations governs the reaction pathways in these materials. THz multidimensional spectroscopic measurements of these materials will provide the first direct experimental evidence that the coupling between these THz vibrations directly governs the pathway, and dynamics, of a reaction. Once this has been demonstrated, in these two diverse sets of materials, this new analytical technique can be applied to many chemical or biological questions, providing an understanding of reaction dynamics on ultrafast timescales - essentially enabling us to watch chemistry happen. This underlying understanding of reactions dynamics will also underpin the future rational design of materials with tailored physical and chemical properties. Following on from measuring the coupling between THz modes using THz multidimensional spectroscopy, specifically designed intense THz pulses will then be used to interact directly with this vibrational motion, essentially controlling and steering the chemical dynamics. This control, coupled with the understanding of reaction dynamics and the associated timescales provided directly by THz multidimensional spectroscopy, leads to a method where reactions can be steered and controlled - with huge potential applications. This fellowship will concentrate on three possible applications for THz-driven dynamics, namely (a) the control of enzymatic reactions, (b) the control of solid state phase transformations (concentrating of pharmaceutically relevant polymorphs) and (c) the control of catalytic reactions.