Research Article

Photoelectron spectra of alkali metal–ammonia microjets: From blue electrolyte to bronze metal

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Science  05 Jun 2020:
Vol. 368, Issue 6495, pp. 1086-1091
DOI: 10.1126/science.aaz7607

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Watching electrons swarm ammonia

Liquid ammonia is unusual in its capacity to host electrons in stable solution, with vivid blue and bronze colors signifying the low- and high-concentration regimes, respectively. Buttersack et al. used photoelectron spectroscopy and accompanying theoretical simulations to track the precise energetic changes that ensued as steadily rising quantities of electrons were introduced by dissolved lithium, sodium, or potassium (see the Perspective by Isborn). The results point to a gradual transition from the dilute electrolyte solution of paired dielectrons to the more delocalized metallic structure at the highest concentrations.

Science, this issue p. 1086; see also p. 1056

Abstract

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.

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