• Buttersack, T.; Mason, P.E.; McMullen, R.S.; Schewe, H. C.; Martinek, T.; Brezina, K.; Crhan, M.; Gomez, A.; Hein, D.; Wartner, G.; Seidel, R.; Ali, H.; Thürmer, S.; Marsalek, O.; Winter, B.; Bradforth, S.E.; Jungwirth, P.: Photoelectron spectra of alkali metal–ammonia microjets: From blue electrolyte to bronze metal. Science 368 (2020), p. 1086-1091

Open Access Version

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 photodetachment 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.