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

Abstract

The reactions of an alkanethiol and a terminal alkenethiol self‐assembled monolayer with NO3 radicals (in the presence of NO2 and O2) were studied. For the alkane monolayer, infrared (IR) spectroscopy and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) confirmed the formation of organonitrates (RONO2). 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 NO3 radicals. The reactive uptake coefficient (γ) of NO3 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 γ value determined in our studies, we show that under conditions where NO3 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 NO3. The results are consistent with the formation of C‐O, aldehyde/ketone, carboxylic groups, and nitrogen containing species.