The line shape of the Auger decay of adatoms is studied by a joint theoretical and experimental effort, the former within a DFT framework, and the latter with synchrotron radiation measurements. We investigate the KL2,3V Auger deexcitation of Na on Al(111), a system with different adsorption geometries. In particular, we study the (root3 x root3)R30degrees phase at 1/3 ML (monolayer) and the more complex (2x2) structure at 1/2 ML coverage. From the comparison between theory and experiment, we unambiguously determine features that allow for the determination of the adsorption environment from the adatom Auger spectrum.
