Dynamics of interfacial reactions between O(³P) atoms and long-chain liquid hydrocarbons

Abstract

Recent progress that has been made towards understanding the dynamics of collisions at the gas-liquid interface is summarised briefly. We describe in this context a promising new approach to the experimental study of gas-liquid interfacial reactions that we have introduced. This is based on laser-photolytic production of reactive gasphase atoms above the liquid surface and laser-spectroscopic probing of the resulting nascent products. This technique is illustrated for reaction of O( 3 P) atoms at the surface of the long-chain liquid hydrocarbon squalane (2,6,10,15,19,23hexamethyltetracosane). Laser-induced fluorescence detection of the nascent OH has revealed mechanistically diagnostic correlations between its internal and translational energy distributions. Vibrationally excited OH molecules are able to escape the surface. At least two contributions to the product rotational distributions are identified, confirming and extending previous hypotheses of the participation of both direct and trapping-desorption mechanisms. We speculate briefly on future experimental and theoretical developments that might be necessary to address the many currently unanswered mechanistic questions for this, and other, classes of gasliquid interfacial reaction.

Dynamics of the Reaction of O(3P) Atoms with Alkylthiol Self-assembled Monolayers

“…43,44,[46][47][48][49]62 A schematic of the revised apparatus is shown in Figure 1. It is a dual-chamber design, with the subsidiary, turbopumped chamber allowing SAM specimens to be stored rapidly under vacuum on removal from their solutions.…”

“…[43][44][45][46][47][48][49] We use laser-induced fluorescence (LIF) spectroscopy to detect the hydroxyl radicals formed at the liquid surface, yielding information on their translational and internal state distributions. This is a development of the earlier work of McCaffery, who was the first to use LIF spectroscopy to detect I 2 inelastically scattered from a range of liquid surfaces.…”

Determining the composition of the vacuum–liquid interface in ionic-liquid mixtures

“…Signal sizes were referenced against interleaved measurements of the well-studied standard, squalane. [32][33][34][35][36][37][38][39][40] To achieve the desired precision, the appearance profiles were averaged over typically ten sets of independent measurements over several different days for each mixture studied. They were corrected for a small background signal caused by a HONO impurity in the chamber by the procedure described previously.…”

Ionic Liquid–Vacuum Interfaces Probed by Reactive Atom Scattering: Influence of Alkyl Chain Length and Anion Volume

“…The LIF-based approach has been applied to squalane (2,6,10,15,19,23-hexamethyltetracosane), widely used as a standard in this field, and other long-chain hydrocarbons and to related self-assembled monolayers. [43][44][45][46][47][48][49][50] The molecular beam approach with mass spectrometric detection was also first applied to squalane and extended to other related surfaces. 9,51-54 5 RAS-LIF detects exclusively the OH products of hydrogen abstraction as they scatter into the gas phase.…”