AuthorJaramillo, Veronica Ines
AdvisorSmith, Mark A.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThis dissertation presents results on the study of temperature dependence on neutral - neutral reactions. In particular OH radical reactions were studied taking advantage of the uniform supersonic expansions produced via a convergent-divergent Laval nozzle. The relative concentration of the OH radical was followed via laser induced fluorescence. The technique and the considerations of the uniform flow reactors used are considered. The method of analysis of the data obtained is also presented. The measurement of rate coefficients for several reactions is reported. These studies demonstrate the utility of this technique as both bimolecular and termolecular reactions have been studied in low temperature environments. Specifically, the temperature dependence of the rate coefficient for the bimolecular reaction, OH + HBr has been investigated at low temperatures (T = 48-224 K) using both the pulsed and continuous uniform supersonic flow reactors. This reaction shows interesting temperature dependence, which can be accurately described with two forms of global fits: UNFORMATTED FORMULA FOLLOWS: k(T) = 1.11 x 10⁻¹¹ [T/298]⁻⁰˙⁹¹ and k(T) = 1.06 x 10⁻¹¹ [T/298]⁻¹˙⁰⁹ exp [(-10.5K)/T] cm³3s⁻¹. UNFORMATTED FORMULA END To aid in understanding this interesting temperature dependence investigations were performed on reactions of OH and OD radicals with HBr and DBr between 120--224 K, using the pulsed uniform supersonic flow reactor. Though the rates are measured by hydroxyl loss, the lack of observed isotopic scrambling indicates the reaction occurs by H/D transfer at all temperatures. The current work provides unequivocal experimental evidence of inverse primary and secondary kinetic isotope effects (kH/kD < 1) at low temperatures. Also reported are measurements of the temperature and pressure dependence of the recombination rate of the atmospherically important reaction OH + NO₂ in both the pulsed and uniform supersonic flow reactor. Employing fall-off behavior analysis, the rate coefficients are compared with the most recent sets of recombination rate measurements obtained at higher temperatures and pressures as well as various rate recommendations. This current recommendation predicts a 20% reduction in the current JPL recommendation for stratospheric conditions.
Degree ProgramGraduate College