Decay of "autoionizing" core-hole states in adsorbed CO molecules

The decay of resonantly excited (1s→2π) C and O $1s$ core-hole states, called autoionization in the gas phase, was studied for absorbed CO molecules by means of angle-resolved Auger spectroscopy for three different systems [CO/Cu(100), CO/Ni(111), CO+K/Ni(111)] which represent rather different bonding configurations. It is shown that the final states resulting from the 2π-participant decay are, unlike the situation for the isolated molecule, not identical to the final states reached in valence photoemission. This is due to the coupling of the 2π level to the substrate valence band and to the dynamics of the screening process. For CO/Cu(100), whose decay spectra differ from those observed for other systems, a decay of two different initial states is proposed.