How O₂‑Binding Affects Structural Evolution of Medium Even-Sized Gold Clusters Au_n^– (n = 20–34)

We report the first joint anion photoelectron spectroscopy and theoretical study on how O₂-binding affects the structures of medium even-sized gold clusters, Au_n^– (n = 20–34), a special size region that entails a variety of distinct structures. Under the temperature conditions in the current photoelectron spectroscopy experiment, O₂-bound gold clusters were observed only for n = 22–24 and 34. Nevertheless, O₂ binding with the clusters in the size range of n = 20–34 can be still predicted based on the obtained global-minimum structures. Consequently, a series of structural transitions, from the pyramidal to fused-planar to core–shell structures, are either identified or predicted for the Au_nO₂^– clusters, where the O₂-binding is in either superoxo or peroxo fashion. The identified global-minimum structures of Au_nO₂^– (n = 20–34) also allow us to gain improved understanding of why the clusters Au_n^– (n = 26–32) are less reactive with O₂ in comparison to others.