Time Dependent Density Functional Theory Study of Magnetic Circular Dichroism Spectra of Gold Clusters Au9(PH3)83+ and Au9(PPh3)83.

Magnetic circular dichroism (MCD) spectroscopy is a source of important data about the electronic structure and optical properties of different chemical systems. Theoretical simulation of the MCD spectra can be used to assist in the understanding of empirically measured MCD spectra. In the present paper, a theoretical investigation of electronic and optical properties of phosphine-protected gold clusters with a Au93+ core with D2h symmetry was performed with time-dependent density functional theory. The influence of ligands on the optical properties of the gold core was investigated. Simulations of the optical absorption and MCD spectra were performed for the bare gold Au93+ cluster as well as for ligand-protected Au9(PH3)83+ and Au9(PPh3)83+ species. MCD spectra were calculated at a temperature of 298 K and a magnetic field of 7 T. A comparative analysis of theoretical and experimental data was also performed. The obtained results show that the theoretically simulated MCD spectrum for the Au9(PPh3)83+ ion in gas phase exhibits a reasonable agreement with experimental results for the [Au9(PPh3)8](NO3)3 system, although with a red shift of up to 0.5 μm-1. Overall, MCD provides significant additional details about the electronic structure of the considered systems compared to the absorption spectra.