Initial Reaction Probability and Dynamics of Ozone Collisions with a Vinyl-Terminated Self-Assembled Monolayer

• Published in: Journal of physical chemistry. C Vol. 115; no. 51; pp. 25343 - 25350
• Main Authors: Lu, Jessica W, Fiegland, Larry R, Davis, Erin Durke, Alexander, William A, Wagner, Alec, Gandour, Richard D, Morris, John R
• Format: Journal Article
• Language: English
• Published: American Chemical Society 29.12.2011
• Subjects: C: Surfaces, Interfaces, Catalysis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp2079692

The gas–surface reaction dynamics of ozone with a model unsaturated organic surface have been explored through a series of molecular beam scattering experiments. Well-characterized organic surfaces were reproducibly created by adsorption of CC-terminated long-chain alkanethiols onto gold, while the incident molecular beams were created by supersonic expansion of ozone seeded in an inert carrier gas to afford control over collision energy. Time-of-flight distributions for the scattered molecules showed near complete thermal accommodation of ozone for incident energies as high as 70 kJ/mol. Reflection–absorption infrared spectroscopy, performed in situ with ozone exposure, revealed that oxidation of the double bond depends significantly on the translational energy of O3. For energies near room temperature, 5 kJ/mol, the initial reaction probability (γ0) for the formation of the primary ozonide was determined to be γ0 = 1.1 × 10–5. As translational energy increased to 20 kJ/mol, the reaction probability decreased. This behavior, along with a strong inverse relationship between γ0 and surface temperature, demonstrates that the room-temperature reaction follows the Langmuir–Hinshelwood mechanism, requiring accommodation prior to reaction under nearly all atmospherically relevant conditions. However, measurements show that the dynamics transition to a direct reaction (analogous to the Eley–Rideal mechanism) for elevated translational energies.