Momentum-Dependent Line Shapes in Photoemission

The crystal-momentum dependence of the line shapes appearing in photoexcitation from the valence levels of ordered S on Fe(100) has been measured with angle-resolved photoelectron spectroscopy. The variation in line shape with $\overrightarrow{\mathrm{k}}$ is a consequence of the hybridization of the energy bands of the two-dimensional overlayer with those of the three-dimensional solid. This observation, predicted theoretically by Liebsch, yields detailed information about the bonding interactions of ordered chemisorption systems.