Photoelectron Angular Distribution Induced by Weak Intermolecular Interaction in Highly Ordered Aromatic Molecules

The photoelectron angular distribution of organic thin films is essential in the discussion of the (opto)­electronic properties from the viewpoints of the spatial distribution of molecular orbitals and the interaction of molecular electronic states. We discuss the role of the weak intermolecular interaction in highly ordered aromatic molecules on the photoelectron angular distribution obtained by angle-resolved photoemission spectroscopy (ARPES). The experimental and theoretical investigation performed for superstructures of polycyclic aromatic hydrocarbons (PAHs) on Au(111) indicates that at least the intramolecular single-scattering process is necessary to be considered in simulation of the orbital tomography. Furthermore, ARPES spectra for various PAH monolayers reveal that the weak π-band dispersion is dependent on the surface Brillouin zone of the monolayer but not of the substrate. The long-range lateral intermolecular interaction in highly ordered aromatic molecules plays a main role in the π-band dispersion. We also discuss the effect of these weak interactions on the orbital tomography.