# Charge State Influence on Stability and Isomerism in Dehydrogenated PAHs: Insights from Anthracene, Acridine, and Phenazine

## TL;DR

This study examines how charge states affect the stability and structure of dehydrogenated PAHs like anthracene, acridine, and phenazine, with implications for chemistry in space and the lab.

## Contribution

The paper reveals how charge state and hydrogen loss influence PAH isomerism and stability, particularly through structural and electronic changes.

## Key findings

- Optimal dehydrogenation sites vary with charge state, affecting PAH stability.
- Adjacent hydrogen loss is common in neutral and singly charged states, while non-adjacent loss occurs in higher charge states.
- Nitrogen atoms and structural symmetry significantly influence reactivity and stability.

## Abstract

In this study, we systematically explored the stability and isomerism of neutral and dehydrogenated polycyclic aromatic hydrocarbons (PAHs) in various charge states, focusing on anthracene, acridine, and phenazine. Our findings highlight key aspects that deepen the understanding of these molecules’ reactivity and stability, relevant in both laboratory and astrophysical contexts. Structural symmetry and the presence of nitrogen atoms significantly impact PAH stability and reactivity. The optimal site for the first dehydrogenation varies with charge state, with notable differences in stability observed across different positions and charge states. For the loss of two hydrogens, there is a clear competition between low and high spin states, influenced by the positions of the hydrogens lost. Infrared spectral analysis reveals characteristic frequencies of conjugated Csp2−Csp2 bonds and variations across different charge states. The elimination of H2 typically occurs at adjacent carbons, forming bonds similar to triple bonds. Reaction networks for anthracene, acridine, and phenazine indicate preferred pathways for hydrogen loss, driven by the need to minimize charge repulsion and maintain aromaticity. Adjacent hydrogen loss is predominant in neutral and singly charged states, shifting to non‐adjacent loss in higher charge states.

The ionization of anthracene, acridine, and phenazine has been explored, along with the removal of one and two hydrogen atoms, to provide valuable information for astrochemists and to understand the behavior of the resulting structures and their electronic reorganization.