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We analyze resonances in the double photoionization of a variety of aromatichydrocarbons. The resonances reflect the breakup of quasi-bound electron pairs.The basic premise of this paper is that there is a direct connection betweenthe quasi-bound pairs and resonant peaks in the optical absorption that areassociated with doubly occupied sites on the perimeter and inside the perimeterof the molecule. The optical absorption leading to the high-energy resonance(approximately 40 eV), calculated from a many-site one-dimensional Hubbardmodel, has a peak at U, the electrostatic interaction energy for two electronswith antiparallel spins on the same carbon atom. In the model, there are alsotwo satellites whose separation from the main resonance is approximately +/-10eV suggesting that unresolved satellite structure may be contributing to thelinewidth of the resonant peak. The low energy resonances (approximately 10 eV)involve carbon atoms located inside the perimeter, a configuration present onlyin pyrene and coronene (among the hydrocarbons studied). In the case of pyrene,which has two carbon atoms inside the perimeter, we employ a two-site Hubbardmodel to characterize the absorption leading to the quasi-bound state. A briefanalysis of the double photoionization resonance of the heterocyclic inorganicmolecule 1,3,5-triazine presented. We also discuss recent results for thedouble photoionization of the cyclic inorganic molecule tribromoborazine andthe organic molecules furan, pyrrole, selenophene, and thiophene where the 2+ion concentration varies linearly with the difference between the photon energyand the threshold energy. A theory for the linear behavior is outlined.

Optical absorption preceding resonant double photoionization of aromatic hydrocarbons hydrocarbons