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Details of Grant 

EPSRC Reference: GR/T20304/01
Title: Systematic laser-driven control of photochemistry
Principal Investigator: Fielding, Professor H
Other Investigators:
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Department: Chemistry
Organisation: UCL
Scheme: Standard Research (Pre-FEC)
Starts: 20 January 2005 Ends: 19 May 2008 Value (£): 744,944
EPSRC Research Topic Classifications:
Gas & Solution Phase Reactions
EPSRC Industrial Sector Classifications:
Chemicals Communications
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Summary on Grant Application Form
During the last few years it has become possible to use femtosecond lasers to control photochemical reactions. The most successful approach has been to shape the femtosecond laser pulse by changing the relative phases between the various wavelengths supported within its broad bandwidth. This has the effect of changing the quantum interferences between the various components of the molecular wave packet launched onto an electronically excited potential energy surface. By combining this phase-control with a learning algorithm that receives feedback from the experiment, it is possible to optimise the phases of the laser field to steer the photochemical reaction along a specific pathway. Shaped optical waveforms can be thought of as a new class of chemical reagent that has the capability of changing the output of a photochemical reaction by making and breaking bonds at will. The technological achievements currently surpass the development of our understanding of the mechanisms of optical control. Thus, despite some truly impressive demonstrations of optical control in organic, organometallic and biological photochemistry, we are still a long way away from possessing the necessary expertise to systematically drive photochemical reactions.This proposal aims to develop this capability. It brings together two well-established groups with expertise in the experimental applications of ultrafast lasers to coherent control (Fielding, UCL) and quantum chemistry calculations of photochemical reactions (Robb, IC). This unique team with its combined strengths in experiment and theory is ideally placed to develop the proposed state-of-the-art machinery to investigate the links between optical phase and the shape of a molecular potential energy surface, and hence to achieve the ultimate goal of being able to drive photochemical reactions intuitively. To guide each experiment, accurate potential energy surfaces will be determined and the photoelectron spectra will be calculated from different points on the surface. Experimentally, the progress of the photochemical reaction will be followed using TRPES, and the shape of the optimised laser pulses will be measured using a commercial instrument. The phase-profile of the optical pulses will be analysed in terms of the momentum distribution in wave packet calculations carried out on the calculated potential energy surfaces. A number of systems will be investigated. The chemistry is interesting per se but they are selected because both the experiment and theory are feasible. In the first instance we will focus on photoisomerisation reactions, in which there is at least one conical intersection between the electronically excited and ground states. The shaped laser pulses will be used to guide the molecules along the excited surface through a conical intersection and into a specific isomer on the ground state. Such systems have been suggested as molecular switches, e.g. azobenzene is an important prototype in the field of molecular electronics and has been used as a trigger in protein folding. Ultimately we aim to be able to design the pulse shapes intuitively.
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