HR: 0800h
AN: A41A-0006    [Abstracts]
TI: Real-time monitoring of ozonolysis of unsaturated SAMs using ATR-FTIR: kinetics, mechanisms and atmospheric implications
AU: * Dubowski, Y
EM: yael@alumni.caltech.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: Vieceli, J
EM: jvieceli@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: Tobias, D J
EM: dtobias@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: Gomez, A
EM: algomez@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: Lin, A
EM: aol@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: Nizkorodov, S A
EM: nizkorod@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: McIntire, T
EM: mcintire@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AU: Finlayson-Pitts, B J
EM: bjfinlay@uci.edu
AF: Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025 United States
AB: The ozonolysis of organics adsorbed on surfaces is of fundamental chemical interest and potentially important in the lower atmosphere. Most previous studies of such systems have monitored in real time the gas phase moiety, while the condensed phase has been analyzed only before and after oxidation. In the present study, the ozonolysis of three carbon and eight carbon vinyl-terminated self-assembled monolayers (SAMs), directly deposited on a silicon ATR (attenuated total reflectance) crystal, was monitored in real-time at 296 K and atmospheric pressure using ATR-FTIR. For comparison, some studies of saturated C8 SAM were also carried out. The films were also characterized by atomic force microscopy and water contact angle measurements. The kinetics of the loss of the vinyl groups and the formation of carbonyl groups were measured as a function of ozone concentrations over the range of 10$^{11}$ to 10$^{16}$ molecules cm$^{-3}$. The measured reaction probabilities are strongly dependent on ozone concentrations and are shown to be consistent with a Langmuir-Hinshelwood mechanism in which ozone is rapidly adsorbed on the surface and then reacts more slowly with the alkene moiety. Molecular dynamics (MD) simulations support this conclusion, showing that ozone does not simply undergo elastic collisions with the surface, but has a significant residence time on it. However, the kinetics measurements indicate a much longer residence time than the MD calculations, suggesting a chemisorption of ozone. Formaldehyde was observed as a gas phase product by infrared cavity ring down spectroscopy. Possible mechanisms of the ozonolysis and its atmospheric implications are discussed.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting