Coulomb pairing resonances in multiple-ring aromatic molecules

TL;DR

This paper analyzes Coulomb pairing resonances in aromatic molecules with multiple rings, revealing high and low energy resonances linked to electron pairing on perimeter and interior carbon sites, respectively.

Contribution

It introduces a Coulomb pairing model to explain observed resonances in photo-double-ionization of multi-ring aromatic molecules, highlighting new localized electron pairing phenomena.

Findings

High energy resonance at ~40 eV linked to perimeter carbon sites

Low energy resonance at 10 eV observed in pyrene and coronene

Anomalous ion ratio increase above 40 eV in most molecules except coronene

Abstract

We present an analysis of the pairing resonances observed in photo-double-ionization studies of CnHm aromatic molecules with multiple benzene-like rings. The analysis, which is based on the Coulomb pairing model, is applied to naphthalene, anthracene, phenanthrene, pyrene and coronene, all of which have six-member rings, and azulene which is comprised of a five-member and a seven-member ring. There is a high energy resonance at ~ 40 eV that is found in all of the molecules cited and is associated with paired electrons localized on carbon sites on the perimeter of the molecule, each of which having two carbon sites as nearest neighbors. The low energy resonance at 10 eV, which is found only in pyrene and coronene, is attributed to the formation of paired electrons localized on arrays of interior carbon atoms that have the point symmetry of the molecule with each carbon atom having three nearest neighbors. The origin of the anomalous increase in the doubly charged to singly charged parent-ion ratio that is found above the 40 eV resonance in all of the cited molecules except coronene is discussed.