Tillmann Buttersack1,2*, Philip E. Mason1 *, Ryan S. McMullen2 *, H. Christian Schewe3 *, Tomas Martinek1 , Krystof Brezina1,4, Martin Crhan1 , Axel Gomez1,5, Dennis Hein6,7, Garlef Wartner6,7, Robert Seidel6,7, Hebatallah Ali3 , Stephan Thürmer8 , Ondrej Marsalek4 †, Bernd Winter3 †, Stephen E. Bradforth2 †, Pavel Jungwirth1 †
Experimental studies of the electronic structure of excess electrons in liquids—archetypal quantum solutes—have been largely restricted to very dilute electron concentrations. We overcame this limitation by applying soft x-ray photoelectron spectroscopy to characterize excess electrons originating from steadily increasing amounts of alkali metals dissolved in refrigerated liquid ammonia microjets. As concentration rises, a narrow peak at ~2 electron volts, corresponding to vertical photo detachment of localized solvated electrons and dielectrons, transforms continuously into a band with a sharp Fermi edge accompanied by a plasmon peak, characteristic of delocalized metallic electrons. Through our experimental approach combined with ab initio calculations of localized electrons and dielectrons, we obtain a clear picture of the energetics and density of states of the ammoniated electrons over the gradual transition from dilute blue electrolytes to concentrated bronze metallic solutions.
