Products and kinetics of the reactions of an alkane monolayer and a terminal alkene monolayer with NO₃ radicals

Abstract

[1] The reactions of an alkanethiol and a terminal alkenethiol self-assembled monolayer with NO 3 radicals (in the presence of NO 2 and O 2 ) were studied. For the alkane monolayer, infrared (IR) spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed the formation of organonitrates (RONO 2 ). The observation of organonitrates is in contrast to the recent X-ray photoelectron spectroscopy (XPS) data, which showed very little nitrogen-containing surface species. The identification of organonitrates may help explain why significant volatilization of the organic chain was not observed in recent studies of alkane monolayer oxidation by NO 3 radicals. The reactive uptake coefficient (g) of NO 3 on alkene monolayers determined in our study is higher than the values obtained in a recent study using liquid and solid alkene bulk films. A possible reason for this difference may be the location of the double bond at the interface. Using the g value determined in our studies, we show that under conditions where NO 3 is high the lifetime of an alkene monolayer in the atmosphere may be short (approximately 20 min). XPS, IR, and ToF-SIMS were used to identify surface functional groups after the oxidation of the alkene monolayers by NO 3 . The results are consistent with the formation of C-O, aldehyde/ketone, carboxylic groups, and nitrogen containing species.Citation: Gross, S., and A. K. Bertram (2009), Products and kinetics of the reactions of an alkane monolayer and a terminal alkene monolayer with NO 3 radicals,

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

“…The nature and yields of the products formed indicate that the mechanism does not closely follow that for gas phase reactions, which has also been reported for oxidation of organics in particles, e.g., by NO 3 and Cl atoms. 57,73,74 The concentration of OH used in these studies, 2.1 Â 10 5 radicals cm À3 , is actually about one to two orders of magnitude smaller than encountered mid-day in the troposphere. 13 Given a reaction probability of unity, the half-life of the CQC group would only be 0.09-0.9 hours for typical mid-day OH concentrations of 2 Â 10 6 to 2 Â 10 7 radicals cm À3 in air.…”

“…Phys., 2010, 12, 9419-9428 | 9425 alkene SAM. 57 In the present experiments, a C8 alkane SAM on Ge was exposed to OH under the same conditions as for the C8Q SAM, but negligible amounts of reaction occurred. D'Andrea et al 53 studied the reaction of OH with a terminal alkene SAM on gold, Au/HS(CH 2 ) 9 CHQCH 2 , and observed that when most of the CQC had reacted, the alkyl chain was intact, consistent with addition to the terminal double bond being the major reaction pathway; however, these experiments were carried out at low pressures in the absence of O 2 .…”

Detailed heterogeneous chemistry in an urban plume box model: reversible co-adsorption of O<sub>3</sub>, NO<sub>2</sub>, and H<sub>2</sub>O on soot coated with benzo[a]pyrene

“…Other trace gases, such as OH and NO 3 , are also involved in important heterogeneous reactions (e.g. Bertram et al, 2001;Molina et al, 2004;Hearn and Smith, 2006;Knopf et al, 2006;Gross and Bertram, 2008;Park et al, 2008;Gross and Bertram, 2009), but have not been shown to adhere to Langmuir adsorption kinetics with subsequent surface reactions (Langmuir-Hinshelwood type reactions) and are therefore not the subject of this study. Although we attempt to use realistic values characteristic of an urban plume scenario as input parameters, our purpose is not to make exact atmospheric predictions.…”

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…Bertram and coworkers, for example, studied the reactions of nitrate radicals with alkane-and alkenethiol self-assembled monolayers on gold substrates in a flow-tube reactor arrangement. 113,114 The reactive uptake coefficients they determined were 8.8 Â 10 À4 for an alkane monolayer and 3.4 Â 10 À2 for an alkene-terminated monolayer. A similar variation in coefficients was found when they compared other alkane and alkene systems.…”

“…In addition to the measurements of reaction rates by Bertram and coworkers, the mechanism of reaction between these monolayers and nitrate radicals was explored using timeof-flight mass spectrometry to detect gas-phase products, while XPS and infrared spectroscopy were employed to analyze the surface-bound molecules following exposure. 114 The reaction was conducted in the presence of atmospheric gases that may have interfered with the reaction of pure NO 3 with the surface.…”