# Independent-subsystem interpretation of the double photoionization of pyrene and coronene

## TL;DR

This paper investigates the double photoionization process in pyrene and coronene, revealing that their ion yields can be modeled as superpositions of independent contributions from perimeter and interior carbon atoms, linked to molecular resonance behaviors.

## Contribution

It introduces a novel interpretation of double photoionization in aromatic hydrocarbons as a superposition of independent subsystems based on molecular structure and resonance states.

## Key findings

- Interior atoms in pyrene show a resonance at 10 eV and linear behavior above 75 eV.
- Coronene exhibits a low energy peak and two pairing resonances, with different contributions from perimeter and central atoms.
- The independence of these contributions relates to Hückel's rule for aromatic stability.

## Abstract

It is shown that the M$^{2+}$ ion yield in the double photoionization of the aromatic hydrocarbons, pyrene and coronene, can be expressed as a superposition of a contribution from a resonance involving carbon atoms on the perimeter and coherent contributions from carbon atoms inside the perimeter. In the case of pyrene, the two interior atoms are associated with a resonance peak at 10 eV and linear behavior above 75 eV. The resonance peak is an optically excited state of the interior carbon pair. The linear behavior arises from the coherent emission of two electrons with equal energy and opposite momenta, as occurs in pyrrole. Coronene has a low energy peak along with two pairing resonances, however, the linear region as in the case of pyrene is absent. The low energy resonance is associated with the atoms on the perimeter and the high energy resonance is associated with the hexagonal array of six carbon atoms at the center of the molecule. It is proposed that the quasi-independence of the contributions from the perimeter and interior atoms is related to H\"uckel's Rule for the stability of aromatic hydrocarbons.