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.