Figure S1, Figure S2, Figure S3, Figure S4, Figure S5, Figure S6, and Figure S7.

Mass spectra of AunO- (n = 5-20) reacting with O2 under high concentration conditions (Figure S1); fittings of the depletion processes of AunO- (Figure S2); the structures corresponding to the adsorption of an O2 for the lowest-lying structures and isomeric structures of AunO- (n = 5-20) (Figure S3); the structures of Aun− (n = 5-20) determined in previous works (Figure S4); the Orbital Delocalization Index (ODI) plots for (a) Au10O- (I) and Au10-(G), (b) Au12O- (G) and Au12- (G), (c) Au14O- (G) and Au14- (G), (d) Au16O- (G) and Au16- (G), and (e) Au20O- (I) and Au20- (G) (Figure S5); the comparisons of the parameters of O2 adsorbed on the five representative AunO-, namely 10-I, 12-G, 14-G, 16-G, and 20-I, and their corresponding gold fragments (Figure S6); the Orbital Delocalization Index (ODI) plots for (a) Au18O- (G) and Au18-(G) and the proposed fragments of Au18O- along with their optimized structures (Figure S7).