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

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 C_sp2-C_sp2 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.