Using the one-dimensional Hubbard model as a guide, the peaks in the double photoionization in a variety of aromatic hydrocarbons and related molecules are analyzed. In all the aromatic hydrocarbons that have been studied, there are peaks in the 2[Formula: see text] ion concentration that are 40 eV above threshold. These peaks arise from the emission of electrons from a Hubbard state associated with carbon atoms on the perimeter of the molecule. Pyrene and coronene also have low energy peaks 10 eV above threshold that are associated with the carbon atoms inside the perimeter. The linear behavior of the 2[Formula: see text] ion concentration above the two-electron ionization energy that is found in organic molecules lacking periodic symmetry in their perimeter atoms is associated with the simultaneous emission of two photoelectrons with approximately equal kinetic energies moving in opposite directions.
Composite quasiparticle formation and the low-energy effective Hamiltonians for the one- and two-dimensional Hubbard model
