Signature of Au as a Halogen

Gold, although chemically inert in its bulk state, is reactive at the nanoscale and, in small clusters, even behaves like a hydrogen atom. Using a photoelectron spectroscopy experiment and first-principles theory, we show that Au also behaves like a halogen in small clusters. This is evident not only in strong resemblance between the photoelectron spectra of Au₂F^- and AuF₂^- but also in Au exhibiting one of the signature properties of halogens, its ability to form superhalogens with electron affinities higher than that of any halogen atom. For example, the electron affinity (EA) of Au₂F^- is 4.17 eV, while AuF₂^-, a known superhalogen, has an EA of 4.47 eV. Of particular interest is Au₂F₂, which, in spite of being a closed-shell system, is a pseudohalogen with an EA of 3.3 ± 0.1 eV. Here, one of the Au atoms behaves like a halogen, making Au₂F₂ mimic the property of AuF₃.