Structural Origin of Spin-Orbit Splitting of 1P Orbitals of Icosahedral Au₁₃ Superatom Protected by Ligands

The key structural factors underlying the spin-orbit (SO) splitting of the 1P orbitals in thiolate-protected Au₁₃ superatoms were investigated using cryogenic anion photoelectron spectroscopy (PES) and two-component density functional theory (2c-DFT) calculations. PES revealed that the 1P orbitals of the Au₁₃ and Au@Ag₁₂ superatomic cores undergo splitting, whereas those of the Ag₁₃ core do not. According to 2c-DFT calculations, the SO splitting of the 1P orbitals of the Au₁₃ superatom stems from the symmetry-dictated coupling between the 6p orbitals of the central Au atom and the 1P orbitals formed by the surrounding icosahedral Au₁₂ shell, both of which are split by SO effects.