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Kinetic studies of the atmospherically implicated halogen oxide radical and peroxy radical cross-reactions

The occurrence of halogen oxide radicals, XO (X = Cl, Br, I), which are formed by the reaction of photolytically released halogen atoms with ozone, has a profound impact on atmospheric chemistry. XO radicals not only react with themselves but they are also believed to react in the atmosphere with other key radical species. In particular, XO can react with peroxy radicals, RO2, which are key members of the so called “odd hydrogen” radical family, HOx. Detailed laboratory studies of the kinetics of reactions of the type XO + RO2 → Products are therefore important in assessing their atmospheric importance and understanding the atmospheric implications of such chemistry. The kinetics of several XO + RO2 (X = Cl or Br and R = H or CH3) reactions have been studied as a function of temperature (T = 210 – 314 K) at p = 760 ± 20 Torr, using the laser flash photolysis technique coupled with UV absorption spectroscopy employing a charge coupled device (CCD) detection system for radical monitoring. Application of CCD detection facilitated the real time monitoring of the XO radical species concentration in each reaction studied. This was afforded by the rapid acquisition of broadband sequential spectra by the CCD where transmitted light intensities were converted into absorbances by Beer’s law. Exploiting the vibronic structure characteristic to XO radicals via ‘differential’ spectroscopy, unequivocal monitoring of XO was afforded by converting the resultant differential absorbances into concentrations using the Beer-Lambert law. The obtained temporal XO concentration profiles were then analysed using detailed numerical models. Strict control of successive experimental conditions and constraints in each fitting model used allowed the initial concentrations of RO2 to be inferred and their temporal behaviour simulated alongside the measured temporal XO profiles to obtain kinetic information on each reaction investigated.
Date January 2014
CreatorsWard, M. K. M.
PublisherUniversity College London (University of London)
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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