Title page for ETD etd-04212011-151825

Type of Document Dissertation
Author Lu, Jessica Weidgin
URN etd-04212011-151825
Title Dynamics of Atmospherically Important Triatomics in Collisions with Model Organic Surfaces
Degree PhD
Department Chemistry
Advisory Committee
Advisor Name Title
Morris, John R. Committee Chair
Deck, Paul A. Committee Member
Long, Gary L. Committee Member
Tanko, James M. Committee Member
Troya, Diego Committee Member
  • Cavity ring-down aerosol spectroscopy
  • Molecular beam
  • Aerosols
  • Ultra-high vacuum
  • Reflection-Absorption Infrared Spectroscopy
  • Self-assembled monolayers
Date of Defense 2011-04-08
Availability unrestricted
Detailed investigations of molecular collisions at the gas-surface interface provide insight into the dynamics and mechanisms of important interfacial reactions. A thorough understanding of the fundamental interactions between a gas and surface is crucial to the study of heterogeneous chemistry of atmospheric organic aerosols. In addition to changing the chemical and physical properties of the particle, reactions with oxidizing gases may alter aerosol optical properties, with implications for the regional radiation budget and climate. Molecular beams of CO2, NO2 and O3 were scattered from long-chain methyl (CH3-), hydroxyl (OH-), vinyl (H2C=CH-) and perfluorinated (CF3(CF2)8-, or F-) ω-functionalized alkanethiol self-assembled monolayers (SAMs) on gold, to explore the reaction dynamics of atmospherically important triatomics on proxies for organic aerosols. Energy exchange and thermal accommodation during the gas-surface collision, the first step of most interfacial reactions, was probed by time-of-flight techniques. The final energy distribution of the scattered molecules was measured under specular scattering conditions (θi = θf = 30°). Overall, extent of energy transfer and accommodation was found to depend on the terminal functional group of the SAM, incident energy of the triatomics, and gas-surface intermolecular forces. Reaction dynamics studies of O3 scattering from H2C=CH-SAMs revealed that oxidation of the double bond depend significantly on O3 translational energy. Our results indicate that the room-temperature reaction follows the Langmuir-Hinshelwood mechanism, requiring accommodation prior to reaction. The measurements also show that the dynamics transition to a direct reaction for higher translational energies. Possible environmental impacts of heterogeneous reactions were probed by evaluating the change in the optical properties of laboratory-generated benzo[a]pyrene (BaP)-coated aerosols, after exposure to NO3 and NO2, at 532 nm and 355 nm by three aerosol analysis techniques: cavity ring-down aerosol spectroscopy (CRD-AS) at 355 nm and 532 nm, photoacoustic spectroscopy (PAS) at 532 nm, and an aerosol mass spectrometer (AMS). Heterogeneous reactions may lead to the nitration of organic-coated aerosols, which may account for atmospheric absorbance over urban areas. Developing a detailed understanding of heterogeneous reactions on atmospheric organic aerosols will help researchers to predict the fate, lifetime, and environmental impact of atmospherically important triatomics and the particles with which they collide.
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