Chemistry Weekly Seminar - Dr. Markus Ammann, Paul Scherrer Institute
Dr. Markus Ammann, Paul Scherrer Institute in Switzerland, will present a seminar at 1:30 pm via Zoom.
Title
Halide oxidation on the surface and in the bulk of environmental materials
Abstract
Oxidation of halides by ozone and photochemically produced radicals is at the origin of cycling of halogen compounds in the atmosphere that affect atmospheric chemistry and climate. Halides are present in the oceans, in sea spray particles, in sea ice and many other environmental compartments. The redox cycling of initial oxidation products in the atmosphere lead to halides being ubiquitously distributed in the atmosphere, including the stratosphere. Kinetic studies have revealed the oxidation of bromide and iodide by ozone being enhanced at interfaces. This has led to a decades long debate about the possible enhanced presence of the heavier and more polarizable halide ions at the aqueous solution – air interface. New surface sensitive X-ray photoelectron spectroscopy work and supporting theoretical calculations largely settle this debate. In addition, they reveal that the reason behind the surface enhanced oxidation reaction rate of bromide is the surface propensity of the first reaction intermediate, a bromide ozonide. Advanced kinetic experiments also unfold subtle details of non-ideality and microphysical properties of concentrated aqueous solutions relevant in the environment that affect the relative roles of surface and bulk oxidation. The environment hosts solutions much more complex than simple halide solutions. We have specifically looked at the interplay of surface active organic compounds with the presence of halide ions at the interface and their oxidation kinetics, which show large differences to the neat aqueous solutions. Thus, molecular level details at complex interfaces play an important role in large scale atmospheric processes, and the combination of surface sensitive spectroscopy with more traditional kinetic tools is crucial to obtain insight in these.
Date: Fridy, October 15, 2021
Time: 1:30 pm
Zoom link available by request from chem.dept@usask.ca