Professor Howard Sidebottom B.Sc. (1966); Ph.D. (1969) both at University of St. Andrews Research interests are in the area of chemical kinetics and photochemistry
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Research Interests
The Chemical Kinetics and Photochemistry Group is involved in studies on the reaction of atoms and radicals in the gas phase. The kinetics of these reactions are investigated by conventional photolytic relative rate methods and by pulsed laser-laser induced fluorescence techniques. Mechanistic studies are carried out by gas chromotography, long-path FTIR spectroscopy and G.C. mass spectrometry. In addition, reactive intermediates are investigated by the use of matrix isolation methods. The main interest in these reactions is in providing an understanding of the factors which influence the reaction rates. The results provide structure-reactivity relationships for the reactions which enable the kinetics and importance of the competing reaction channels for elementary reactions to be estimated.
Of current interest is the determination of kinetic and mechanistic data for the reactions of hydroxyl and alkoxy radicals uch of the research effort of the group is focused on atmospheric chemistry. The relationship between concentrations of secondary pollutants (oxidants) impacting on a given geographical location under a set of meteorological conditions to the emission levels of primary pollutants is a major goal of atmospheric chemists. In order to understand the fate of volatile organic compounds in the atmosphere, the rate and chemical mechanisms of the reactions converting these species into secondary pollutants must be evaluated for various atmospheric conditions. Reactions are carried out under laboratory conditions using conventional rapid reaction relative rate and pulsed excitation rate methods. Product distribution studies are performed using GC, long-path FTIR spectroscopy and GC/MS analytical techniques. Atmospheric simulation experiments are also carried out at the European photoreactor laboratory in Valencia, Spain which has two large outdoor reaction chambers on the top of the building. Photooxidations of volatile organic compounds are performed at parts per billion levels as a function of relative humidity and variations in the concentrations of nitrogen oxides. In situ concentration measurements of reactants and products are made using FTIR and UV-vis spectrometers fitted with multiple pass optical systems (pathlength 300 to 500 meters). Samples can also be withdrawn for analyisis by HPLC/MS and GC/MS while chemiluminescence analysers are available for monitoring nitrogen oxides and ozone. It is also possible to monitor hydroxyl radical concentrations using a laser induced fluorescence technique. Degradation mechanisms for a large range of organic compounds can be developed from studies on a number of generic species and the results used for input into photochemical trajectory models of the troposphere. Such computer models may be used to predict the levels of oxidant formation in the troposphere arising from organic compounds released from natural sources, combustion processes and solvent uses. At present investigations are being carried out in conjunction with a number of European universities on the possible reduction in tropospheric oxidant levels by the: Employment of alternative solvents; Use of new fuel formulations; Replacement of chlorinated solvents.
The European Photoreactor, Valencia
- H. Sidebottom and J. Franklin.The atmospheric fate and impact of hydrochlorofluorocarbons and chlorinated solvents. Pure and Appl. Chem., 68, 1757 (1996).
- J. Barry, G. Locke, D. Scollard, H. Sidebottom, J. Treacy, C. Clerbaux, R. Colin and J. Franklin1,1,1,3,3-Pentafluorobutane (HFC-365mfc) atmospheric degradation and contribution to radiative forcing.Int. J. Chem. Kinet., 29, 607 (1997).
- J. Treacy, M. Curley, J. Wenger and H. Sidebottom.Determination of Arrhenius parameters for the reactions of ozone with cycloalkenes. J. Chem. Soc. Faraday Trans., 93, 2877 (1997).
- E. Porter, J. Wenger, J. Treacy, H. Sidebottom, A. Mellouki, S. T~Bton and G. Le Bras. Kinetic studies on the reactions of hydroxyl radicals with diethers and hydroxyethers. J. Phys Chem. A., 101, 5770 (1997).
- J. Wenger, E. Porter, E. Collins, J. Treacy and H. Sidebottom Mechanisms for the chlorine atom initiated oxidation of dimethoxy methane and 1,2-dimethoxy ethane in the presence of NOx. Chemosphere, 38, 1197 (1999).
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