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Details of Grant 

EPSRC Reference: EP/D003679/1
Title: Dynamics of reactions at the surfaces of liquids and self-assembled monolayers
Principal Investigator: McKendrick, Professor KG
Other Investigators:
Costen, Professor ML Cooke, Professor G Westacott, Dr R
Researcher Co-Investigators:
Project Partners:
Department: Sch of Engineering and Physical Science
Organisation: Heriot-Watt University
Scheme: Standard Research (Pre-FEC)
Starts: 01 November 2005 Ends: 31 July 2009 Value (£): 387,915
EPSRC Research Topic Classifications:
Gas & Solution Phase Reactions Surfaces & Interfaces
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:  
Summary on Grant Application Form
This proposal concerns the chemical reactions that take place at the boundary between a gas and a liquid, or at a special model of a liquid surface known as a self-assembled monolayer.A lot is already known about what happens when molecules collide and react in gases. Because the molecules in gases are spaced relatively far apart, when they do meet each pair interacts effectively in isolation. These individual reactions can be described accurately at a level of fine detail by sophisticated theories. Sequences of them are responsible for many important phenomena, such as the creation and destruction of the Ozone Layer, and the burning of hydrocarbon fuels.The reactions of gases at the surfaces of solids, particularly certain metals, are also very important. Most people are familiar, for example, with catalytic converters that remove undesirable gases from car exhausts. Gas-solid reactions are more complex systems than simple gases because of the much larger number of atoms involved. However, this is simplified by the metal's rigidity, which normally prevents the gases from penetrating below the outer layer of atoms. Solid structures also tend to be very regular. This makes it much easier to describe them theoretically because, in effect, only the atoms in a single repeating unit have to be considered.Contrast this with reactions at the boundary between a gas and a liquid. Much less is known in any detail about what happens there. In the bulk of a liquid, the molecules are almost as closely packed together as in a solid. Interactions between neighbouring molecules certainly couldn't be ignored. However, the boundary between the liquid and the gas is often much less sharp than between a gas and a solid. Rather than picturing it as smooth and hard like a piece of glass, at an atomic scale the surface is probably much looser and softer. Molecules attacking from the gas may be able to penetrate to different depths, but the details of this are far from being properly understood. Because there are no regular repeating units, a large number of atoms need to be treated theoretically.We will study these gas-liquid reactions using a new method that we have developed. Oxygen atoms are created just above the surface using a laser beam to break up precursor molecules in the gas. The liquid will be composed of long-chain hydrocarbons, similar to those used to lubricate machines. The oxygen atoms will pull off hydrogen atoms, creating OH (hydroxyl) radicals. Because of the chemical energy that's released, the OH will initially be moving at high speed, rotating (tumbling end-over-end) and vibrating (like two weights connected by a spring). If it escapes directly back into the gas, it will carry these motions away with it. However, if it becomes entangled and temporarily trapped, it will give up some of its energy. The crux of our experiment is to take a snapshot of the OH radicals as they leave the surface and find out what types of energy they have. We will do so by detecting how they absorb and re-emit light from another laser fired a few microseconds after the first one. To help us understand how what we see is related to the structure of the liquid, we will also study reactions with self-assembled monolayers. These are thin layers of molecules of a similar type to those in the liquid, but attached to a solid support that causes them to pack together in a well-defined way.Despite much less being known about them, these gas-liquid reactions are still very important. They are, for example, particularly crucial in the atmosphere, especially at the surfaces of the microscopic particles known as aerosols. These are involved in the chemical conversion of key atmospheric constituents, and act as the nuclei from which cloud droplets are formed. The more general scope of important gas-liquid interactions spans industrial processes such as oxidation of lubricants through to the uptake of oxygen in human lungs.
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Organisation Website: http://www.hw.ac.uk