Session: Physical Chemistry Poster:

Few anions exhibit electronically excited states, and, if they do, the one, or maybe two, possible excitations typically transpire beyond the visible spectrum into the near-infrared. These few, red-shifted electronic absorption features make anions tantalizing candidates as carriers of the diffuse interstellar bands (DIBs), a series of mostly unknown, astronomically ubiquitous absorption features documented for over a century. The recent interstellar detection of benzonitrile implies that cyano-functionalized polycyclic aromatic hydrocarbon (PAH) anions may be present in space. This quantum chemical work explores the electronic properties of deprotonated benzene, naphthalene, and anthracene
anions functionalized with a single cyano group. The larger anions possess both valence and dipole bound excitations in the 450 nm to 900 nm range with oscillator strengths for both types of $> 1 \times 10^{-4}$. The valence and dipole bound excited state transitions will produce slightly altered substructure from one another making them appear to originate with different molecules. The known interstellar presence of related molecules, the two but differing nature of the excited states for each, and the wavelength range of peaks for these cyano-functionalized PAH anions are coincident with DIB properties. Finally, the methods utilized appear to be able to predict the presence of dipole-bound excited states within a 1.0 meV window relative to the electron binding energy.

Ryan Fortenberry

The University of Mississippi

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