Photoelectron spectroscopy of the solvated anion clusters O−(Ar)n=1–26,34: Energetics and structure

Negative ion photoelectron spectra of the solvated anion clusters O−(Ar)n=1–26,34 have been recorded. Vertical detachment energies obtained from the cluster anion spectra were used to determine total as well as stepwise stabilization energies. An examination of these energetic values as a function of cluster size demonstrates that the first solvation shell closes at n=12. Furthermore, magic numbers in the energetic data and in the mass spectrum suggest O−(Ar)n clusters of sizes n=12–34 are structurally very similar to homogeneous rare gas clusters and follow a polyicosahedral packing pattern, implying O−(Ar)12 has an icosahedral structure and O−(Ar)18 has a double icosahedral structure. The solvated cluster anion photoelectron data were also analyzed using a generalized cluster size equation, which relates the cluster anion data to bulk parameters. The data for O−(Ar)n≥12 is well represented by the theoretical prediction and was therefore used to estimate several bulk parameters, including the photoemission threshold, the photoconductivity threshold, and the bulk solvation energy.