  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.
