  We discuss the spectroscopic fingerprints that a surface Mott-Hubbard
insulator should show at the intra-atomic level. The test case considered is
that of the Si-terminated SiC(0001) sqrt{3}xsqrt{3} surface, which is known
experimentally to be insulating. We argue that, due to the Mott-Hubbard
phenomenon, spin unpaired electrons in the Si adatom dangling bonds are
expected to give rise to a Si-2p core level spectrum with a characteristic
three-peaked structure, as seen experimentally. This structure results from the
joint effect of intra-atomic exchange, spatial anisotropy, and spin-orbit
coupling. Auger intensities are also discussed.
