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Details of Grant 

EPSRC Reference: EP/L025833/1
Title: Infrared emission from the quenching of electronically excited states
Principal Investigator: Ritchie, Professor GAD
Other Investigators:
Hancock, Professor G
Researcher Co-Investigators:
Project Partners:
Department: Oxford Chemistry
Organisation: University of Oxford
Scheme: Standard Research
Starts: 01 December 2014 Ends: 30 November 2017 Value (£): 338,280
EPSRC Research Topic Classifications:
Analytical Science Gas & Solution Phase Reactions
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
08 May 2014 EPSRC Physical Sciences Chemistry - May 2014 Announced
Summary on Grant Application Form
When a molecule absorbs light to form an excited state, its total energy increases, it is no longer in equilibrium with its surroundings, and processes will naturally occur to counteract this and thereby restore equilibrium. For an electronically excited bound state (where the absorption is in the visible or ultraviolet region of the spectrum), the process of energy loss can take place through emission of light (fluorescence) or by collisional processes (quenching). Fluorescence is well understood, as are the rates of quenching, but what is far less understood are the specific fates of the quenched species - where does the (considerable) energy contained in the excited state go - does it appear in kinetic or internal energy of the ground state product and if chemical reaction is possible, what are the products and are they formed with internal energy?

The purpose of this study is to investigate the products of the quenching of two important gas phase free radical species, OH and NO. They will be formed in their electronically excited states by absorption of ultraviolet photons (at 308 nm and 226 nm respectively), and the products observed by the technique of Time Resolved Fourier Transform InfraRed Emission (TRFTIRE) using an apparatus unique to the UK. The first system to be studied will be the quenching of the OH(A) state in collisions with molecular hydrogen. Here the main result of quenching is the formation of water, and preliminary results have shown that the water is hot, with a great deal of the available energy appearing as vibration, and resulting in emission in the mid-infrared region of the spectrum. The emission spectrum of H2O will be compared with the complementary results already obtained for this reaction by Lester's group on the H atom cofragment kinetic energy distribution, and the internal energy distribution in the OH ground state product of inelastic quenching. State of the art calculations of the quenching processes will be carried out by our theoretical partners.

Other systems to be studied include the quenching of OH(A) by O2, CO and CO2, where atomic reaction products have been observed - our studies will complete the picture by looking for the first time at the molecular reaction products. Similar studies on the NO(A) state will also be carried out. The results are of importance in interpreting the laser induced fluorescence measurements in combustion systems, where quenching processes can result in a serious overestimation of the radical concentrations.
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Organisation Website: http://www.ox.ac.uk