Electronic and geometric properties of exohedral sodium- and gold-fullerenes

The electronic and geometric properties of gas-phase exohedral ${\mathrm{C}}_{\mathrm{60}}{\mathrm{Na}}_N^{-},$ ${\mathrm{C}}_{\mathrm{70}}{\mathrm{Na}}_N^{-},$ and ${\mathrm{C}}_{\mathrm{60}}{\mathrm{Au}}_N^{-}$ cluster anions are investigated. Time-of-flight mass spectrometry and photoelectron spectroscopy (PES) reveal complex-specific arrangements of the sodium and the gold atoms on the fullerene cage. The electron affinity of ${\mathrm{C}}_{\mathrm{60}}{\mathrm{Au}}_N$ clearly shows even–odd alternation with the number of Au atoms, which suggests a “dry” structure where Au atoms aggregate as a cluster on the ${\mathrm{C}}_{\mathrm{60}}.$ In contrast, ${\mathrm{C}}_{\mathrm{60}}{\mathrm{Na}}_N$ and ${\mathrm{C}}_{\mathrm{70}}{\mathrm{Na}}_N$ show a “wet” structure having the Na atoms packed into stable trimers on the surface. For ${\mathrm{C}}_{\mathrm{60}}{\mathrm{Na}}_N$ $\text{(N=0}$ to 4), PES experiments at a high photodetachment energy (5.81 eV) allow us to deduce the net charge transferred from the sodium atoms to the lowest unoccupied molecular orbital of the fullerene. For larger ${\mathrm{C}}_{\mathrm{60}}{\mathrm{Na}}_N,$ moreover, a metallic transition is shown to occur at $\text{N∼13,}$ and analysis of the adiabatic electron affinity variations allows the identification of the first magic sizes corresponding to electronic shell closure in the sodium layer.