Optical absorption by magnesia-supported gold clusters and nanocatalysts: effects from the support, cluster and adsorbants

Polarization-resolved optical spectra of magnesia-supported gold clusters Au$_N$/MgO (N=1,2,4,8), bound at a surface color center $F_s$ of the MgO(100) face, are calculated from the time-dependent density functional theory. The optical lines for n=1,2 are dominated by transitions that involve strong hybridization between gold and $F_s$ states whereas for n=4,8 intracluster transitions dominate. The theoretical optical spectra are sensitive to cluster structure and adsorbants (here CO and O$_2$ molecules on Au$_8$/MgO) which suggests polarization-resolved optical spectroscopy as a powerful tool to investigate structures and functions of chemically active, supported clusters.