Prof. Pavel Jungwirth
March 14th, 3:30 pm Seminar Title: Electrons in Polar Solvents: Birch Reduction, Blue Electrolytes, and Golden Metals
Abstract:
Liquid ammonia is well-known as a solvent that sustains long-lived solvated electrons formed by the dissolution of alkali metals. Solvated electrons act as powerful chemical reducing agents and, as such, find applications in numerous reduction processes both in organic chemistry and biochemistry. Probably the best-known example is the Birch reduction of benzene in the environment of liquid ammonia with the addition of an alkali metal (as a source of solvated electrons) an aliphatic alcohol. Here we discuss how we have characterized the electronic structure of alkali metal – liquid ammonia mixtures at concentrations spanning from blue electrolytes to bronze colored metallic solutions by means of photoelectron spectroscopy in liquid microjets aided by ab initio molecular dynamics simulations and quantum chemical calculations.
The above alkali metal solutions of liquid ammonia with electrolyte or metallic properties have been known for centuries now. But how about water as a solvent? It it is a textbook knowledge that dissolution of alkali metals in water leads to an explosive chemical reaction, thus only low (sub-metallic) electron concentrations have been prepared so far. Here we show that we have now found a way around the explosive chemistry by adsorbing water vapor at a pressure of about 10-4 mbar onto a train of liquid sodium-potassium alloy drops ejected from a nozzle into a vacuum chamber. This leads to a formation of a transient gold-colored layer of water doped with ~51021 electrons/cm3, the metallic character of which is demonstrated by a combination of optical reflection and synchrotron x-ray photoelectron spectroscopies.
Faculty Host: Gil Nathanson