Chemical complexity and the role of condensed film structure: methane adsorption and Propene Oxidation Michelle Brann 1,2 , Rebecca Thompson 1,3 , Steven J. Sibener 1 1 Department of Chemistry and The James Franck Institute, 929 East 57th Street, University of Chicago, Chicago, Illinois 60637, 2 National Institute of Standards and Technology (NIST), 100 Bureau Dr,Gaithersburg, MD 20899, 3 Department of Chemistry, St. Edward's University, 3001 South Congress Austin, Texas 78704 This poster will examine the molecular adsorption and oxidative reactivity of small hydrocarbons (methane and propene) in the condensed phase. The systems experimentally model surface-mediated processes occurring on icy-dust grains to develop a more complete understanding of the formation of planetary atmospheres, complex organic molecules, and origin of life in the universe. These studies were conducted in a state-of-the-art ultra-high vacuum gas-surface scattering chamber equipped for operation involving cryogenic substrates. The chamber is connected to a differentially-pumped supersonic molecular beam line that produces reactant gases with highly- tunable kinetic energies for exposure. First, we examined the sticking probability of methane on deuterium oxide ice films with varying porosities and crystalline structures. Changes on the surface are monitored in real-time with Reflection Absorption Infrared Spectroscopy (RAIRS) and King and Wells mass spectrometry techniques. We found that the sticking probability of high energy methane is greatest for the porous films. These results suggest that porous films are more efficient at dissipating energy and that the morphology of frozen films may greatly impact the subsequent concentration and reactivity of adsorbates. To further understand how ordering in condensed films can have impact on reactivity, we next examined the oxidative reactivity of thin films of propene with particular interest towards propene epoxidation. After exposing propene to a supersonic beam of ground state atomic oxygen, O( 3 P), RAIRS spectra confirm significant propene reactivity towards a variety of products including the epoxide. Moreover, propene film thickness and ordering in the multilayer does influence oxygen penetration and mobility within the film, and therefore the resulting product formation. This work provides fundamental mechanistic insight into the sticking, diffusion, and reactivity of small molecules in condensed films. This work is critical to create accurate models of the chemical and physical processes occurring in atmospheric and terrestrial environments and to determine planetary atmospheres’ gas compositions. Ultimately, this will help us to better understand formation of solar systems and the origin of lifein the universe. References 1. Thompson, R. S.; Brann, M. R.; Sibener, S. J. Sticking Probability of High-Energy Methane on Crystalline, Amorphous, and Porous Amorphous Ice Films. Phys. Chem. C 2019 , 123 , 17855–17863. 2. https://pubs.acs.org/doi/10.1021/acs.jpcc.9b03900 Brann, M. R.; Thompson, R. S.; Sibener, S. J. Reaction Kinetics and Influence of Film Morphology on the Oxidation of Propene Thin Films by O( 3 P) Atomic Oxygen. Phys. Chem. C 2020 , 124 , 7205–7215. 3. https://pubs.acs.org/doi/10.1021/acs.jpcc.9b11439 Brann, M. R.; Hansknecht, S. P.; Ma, X.; Sibener, S. J. Differential Condensation of Methane Isotopologues Leading to Isotopic Enrichment under Non-Equilibrium Gas–Surface Collision Conditions. Phys. Chem. A 2021 , 125 , 9405–9413. https://pubs.acs.org/doi/10.1021/acs.jpca.1c07826
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