Interaction of Gas-Phase Ozone at 296 K with Unsaturated Self-Assembled Monolayers:  A New Look at an Old System

Abstract

The oxidation of organics adsorbed on surfaces by ozone is of fundamental chemical interest and potentially important in the lower atmosphere. Studies of the oxidation of the three-carbon and eight-carbon vinylterminated self-assembled monolayers (SAMs, C3d and C8d) on a silicon ATR (attenuated total reflectance) crystal by gas-phase O 3 at 296 K are reported. Oxidation of the SAMs was followed in real time by ATR-FTIR using ozone concentrations that spanned 5 orders of magnitude, from ∼10 11 to 10 16 molecules cm -3 . For comparison, some studies of the saturated C8 SAM were also carried out. The films were also characterized by atomic force microscopy and water contact angle measurements. The loss of CdC and the formation of CdO were measured in real time and shown to be consistent with a Langmuir-Hinshelwood mechanism in which O 3 is rapidly adsorbed on the surface and then reacts more slowly with the alkene moiety. This is supported by molecular dynamics (MD) calculations which show that O 3 does not simply undergo elastic collisions but has a significant residence time on the surface. However, the kinetics measurements indicate a much longer residence time than the MD calculations, suggesting a chemisorption of O 3 . 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.

The Oxidation of Oleate in Submicron Aqueous Salt Aerosols: Evidence of a Surface Process

“…49,53,54 However, our measured reactive uptake coefficient was a factor of 10 lower than the measurements made on TASAMs by Moise and Rudich. 49 One explanation for this difference may be that the oleate double bond lies in the center of the molecule and is therefore likely to be less accessible than in the TASAMs.…”

“…High-molecular-weight oligomers have been detected upon oleic acid ozonolyis; 41,42,[53][54][55] perhaps nonanoic acid is a monomer unit in such oligomers and is released during the 0.5 s of heating in the presence of water vapor that precedes detection. At sufficiently high concentrations, fatty acids under neutral to acidic conditions form oil or lamellar phases, or crystals depending on temperature and pH.…”

“…[48][49][50][51][52] Both volatile and involatile products of oleic acid ozonolysis have been identified, including nonanaldehyde, nonanoic acid, 9-oxononanoic acid, and azelaic acid. 38,46,48 It has also been suggested that ozonolysis may lead to polymerization in pure oleic acid particles 41,42 and for other unsaturated organics in self-assembled monolayers 53,54 and thin films. 55 Overall, existing experimental data suggest that the reactive uptake coefficient, γ O 3 , for O 3 on pure oleic acid is on the order of 10 -3 at room temperature.…”

UV Photodissociation Spectroscopy of Oxidized Undecylenic Acid Films

“…39,41,42,71 It is likely that the initial splitting of POZ occurs with nearly equal probability for the formaldehyde and sebaldehydic acid channels. Indeed, (II) and (VIII) are generated in comparable amounts in the oxidized film.…”

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations

“…The coating was repeated using 10 min exposure time, followed by boiling three times in dichloromethane after which the crystal was wiped using dichloromethane to remove physisorbed residues. 27,31 After coating, the ATR crystal was placed in the reaction cell under a flow of dry nitrogen overnight.…”