Laine, Patrick L.
Laser flash photolysis studies of halogen atom reactions of atmospheric interest.
Degree: PhD, Earth and Atmospheric Sciences, 2011, Georgia Tech
The Earth's atmosphere is a large photochemical reactor consisting primarily of N2 (~78%) and O2 (~21%) with Ar and water vapor being the next most abundant constituents. All of the remaining gases in the atmosphere are referred to as 'trace gases', and they play a critical role in understanding climate change, urban air quality, ozone production and depletion, and in determining the overall 'health' of the atmosphere. These trace components are present in our atmosphere with mixing ratios, i.e., mole fractions, ranging from sub parts per trillion to several hundred parts per million. One class of trace constituents that play a critical role in atmospheric chemistry are free radicals. Free radicals are highly reactive, often initiating the oxidation of natural and anthropogenic atmospheric species, thereby often controlling the fate and lifetimes of these species. The research comprising this dissertation focuses on laboratory studies of the kinetics and mechanisms of free radical (atomic halogen) reactions that can impact the levels of important trace atmospheric species. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of Cl or Br atoms to investigate halogen atom chemistry. The research addresses three groups of reactions: Cl atom reactions with alkyl bromides, Cl and Br-initiated oxidations of small (C2-C6) alkenes, and Cl reactions with CH3SCH3 (DMS, dimethylsulfide) and CH3SeCH3 (DMSe, dimethylselenide).
The alkyl bromide reactions were experimentally unique in that we were able to deduce kinetics of the Cl atom reaction with bromoethane, n-bromopropane, and 1,2-dibromoethane by monitoring the appearance of the Br product by LFP-RF. The Br is formed via elimination that occurs essentially instantaneously following β-H abstraction by the Cl atom. All three of the bromoalkanes investigated are emitted into the atmosphere primarily from anthropogenic sources and all three have been identified by the World Meteorological Organization (WMO) as very short-lived (lifetime less than 6 months) source gases with significant ozone depletion potentials (ODPs). Additionally, the bromoalkanes mentioned above have been of interest as model compounds for larger partially halogenated organics found in the atmosphere, and they have been considered as potential replacement compounds for chlorofluorocarbons (CFCs) that have been banned as a result of the Montreal Protocol. Brominated very short-lived compounds are thought to contribute 20-25% of total stratospheric bromine. Thus, there is considerable interest in understanding the atmospheric chemistry of even the most short-lived organic bromine compounds. Temporal profiles of Br atoms provided important kinetic and mechanistic insight for the reactions over a wide range of temperature and pressure. Temperature-dependent rate coefficients are determined for the alkyl bromides of interest for the first time, and the potential importance of the Cl reaction as an…
Advisors/Committee Members: Paul Wine (Committee Chair), Athanasios Nenes (Committee Member), Greg Huey (Committee Member), Rodney Weber (Committee Member), Thomas Orlando (Committee Member).
Subjects/Keywords: Bromine atom reactions; Chlorine atom reactions; Halogen atoms; Gas phase reactions; Free radical reactions; Free radicals (Chemistry); Chemical reactions; Thermochemistry; Atmosphere; Atmosphere Laser observations
The research addresses three groups of reactions: Cl atom reactions with alkyl bromides… …each alkyl bromide is qualitatively assessed.
The studies of halogen atom reactions with… …x29; Br atom reactions with olefins involving the formation of weakly bound Br
adducts (… …Ch. 5), and (iv) Cl atom reactions with the most abundant natural sulfur and… …reactive towards most hydrocarbons
Br atom reactions with saturated hydrocarbons proceed slowly…
to Zotero / EndNote / Reference
APA (6th Edition):
Laine, P. L. (2011). Laser flash photolysis studies of halogen atom reactions of atmospheric interest. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/42817
Chicago Manual of Style (16th Edition):
Laine, Patrick L. “Laser flash photolysis studies of halogen atom reactions of atmospheric interest.” 2011. Doctoral Dissertation, Georgia Tech. Accessed January 27, 2021.
MLA Handbook (7th Edition):
Laine, Patrick L. “Laser flash photolysis studies of halogen atom reactions of atmospheric interest.” 2011. Web. 27 Jan 2021.
Laine PL. Laser flash photolysis studies of halogen atom reactions of atmospheric interest. [Internet] [Doctoral dissertation]. Georgia Tech; 2011. [cited 2021 Jan 27].
Available from: http://hdl.handle.net/1853/42817.
Council of Science Editors:
Laine PL. Laser flash photolysis studies of halogen atom reactions of atmospheric interest. [Doctoral Dissertation]. Georgia Tech; 2011. Available from: http://hdl.handle.net/1853/42817